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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification Concerns International Journal of Forecasting 25 (2009) 716–733

www.elsevier.com/locate/ijforecast

Decision

By Mr. George-Sp. C. ATHANASOPOULOS Introduction Harvard University, Graduate School of Design, Student, making and planning under low levels of predictability By Mr. George-Sp. C. ATHANASSOPOULOS Architect Student of the School of Architecture b,1 Technical University of Crete Spyros Makridakis a,∗ , Nassim Taleb

a INSEAD, Boulevard de Constance, 77305 Fontainebleau, France 1. Introductory approach: Defining the concept b Polytechnic Institute of NYU, Department of Finance and Risk Engineering, Six MetroTech Center, Rogers Hall 517, 1. Introductory approach: the concept (444 BC - 370 BC, Athens), Brooklyn,philosopher, NY 11201, USA ANTISTHENIS, the ancientDefining Greek ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term Abstract 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification This specialas section aimsas to the demonstrate the limited high level of uncertainty in practically all important Sociology well), “refining” of apredictability city area,and the removal from this, (in various areas of our the implications of this. summarizes huge body ofplacement solid empirical evidence accumulated Sociology asand well), as the “refining” of a citythearea, fromthere this, of (in variousover ways), oflives, social groups, usually ofIt low-income andthe theremoval artists, the past several decades that proves the disastrous consequences of inaccurate forecasts in areas ranging from the economy and ways), of social groups, usually of low-income and the placement there of artists, the operation art galleries, restaurants, However this “change”, of alike, business to floods andof medicine. The big problem is, however,etc. that the great majority of people, decisionregardless and policy makers the operation of art galleries, restaurants, etc. However this “change”, regardless of still believe not other only that consequences accurate forecasting ishas, possible, but also also that uncertainty reliably assessed. Reality, however, whatever results rising can of beland prices (and the shows otherwise, as this special section proves. This paper discusses forecasting accuracy and uncertainty, and distinguishes whatever other consequences has, results also rising of land prices (and the potential relative speculation). three distinct types of predictions: those relying on patterns for forecasting, those utilizing relationships as their basis, and those potential relative speculation). Thehuman term gentrification found atoffirst in theInUK in early 1960s andand it refers tofacing for which judgment is the majorisdeterminant the forecast. addition, the major problems challenges Theand term gentrification found firstreliably in the UK in early and refers forecasters the reasons why uncertainty cannot be at assessed discussed using 1960s fourin large data it sets. Thereof isto also a the then observed trend ofiswealthy people toare buy property poor areas summary of the eleven papers included thiswealthy special section, as well as concluding remarks theare need the then observed trend people tosome buy property inemphasizing poor areas ofto be London, upgrade them, stayinof themselves sometimes there and thus old residents rational and realistic about our expectations and avoid the common delusions related to forecasting. London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. c 2009 International Institute of Forecasters. Published by Elsevier B.V. All rights reserved. being indirectly “squeezed”. A description of this phenomenon is included in the work of Sociologist Ruth Keywords: Accuracy; Uncertainty; Low level predictability; Non-normalin forecasting errors; Judgmental predictions Ruth A Forecasting; description ofperiod, this phenomenon is situations included the recorded work of Sociologist GLASS at the same while similar were in other major GLASS at the same period, situations were recorded in other major cities in Western countries, bywhile othersimilar Researchers. in Western countries, by other Researchers. 1.cities Introduction all forecasters dismal. Worse, the accuracy Since then, the issue has preoccupied almost several scholarsis and for its more ofseveral “scientific”scholars forecasters and is often no its better than that Since then, the issue has preoccupied for more comprehensive being below, from the various The unknown future approach is a source of are anxiety, givingsummarized of simple benchmarks (e.g. today’s value, or some comprehensive approach are being summarized below, from the various interpretations of the of gentrification, the following: rise to a strong human need phenomenon to predict it in order to average). In addition, the basis of their predictions is interpretations of theitsphenomenon thecategory following: reduce, ideally the eliminate, inherent is uncertainty. In aorsense, phenomenon dueof togentrification, a trend ofasa doubtful new ofaugurs socialand groups often as those of astrologists. The demand for forecasts has created an ample supply In the area of economics, who predicted the subprime to “return” to the city, leaving the purlieus for several reasons: high costs in money of “experts” to fulfill it, from augurs and astrologists to and credit crunch crises,place the Internet bubble, the Asian and timeand to travel purlieus to downtown, where work is, lack of the economists businessfrom gurus. the Yet the track record of contagion, the real estate and savingswas and born loans crises, 1. The term comes from Sociologist Ruth GLASS, 1912-1940. Ruth GLASS sense of safety at the distributed residencies outside town centres, search for betterin American lending calamity, the other Berlin, where she made her first studies. In 1932 the sheLatin published an important study and entitled: ∗ Corresponding editor. Tel.: education, +30 6977661144. entertainment “at the heart of the city”, (possibly) services of health, major disasters? In business, who “predicted” Youth Unemployment. The same year she left Germany and after continuous movements for the E-mail addresses: smakrid@otenet.gr (S. Makridakis), lower living cost of,(N. “withdrawal” from private car access to markets, etc.whereAIG, collapse of Lehman Bear Stearns, studies and research in Geneva, Prague, London and Neweasier York she cameBrothers, back to London, nnt@fooledbyrandomness.com Taleb). 1inTel.: 1943 she studies cityphenomenon planning. 1950 she teacher in the Enron orIn WorldCom (in the and Northern Rock, +1 718 260 published 3599; +1 718 260approach, 3355.regarding According tofax: another the is due tobecame a USA), systematic and University informal College of London, where she continued her social research. brokers Her public action and long-term effort by organized groups, manufacturers, of buying c 2009 International 0169-2070/$ - see front matter Institute of justice. Forecasters.See Published Elsevier B.V.ENGLISH All rights reserved. her work are characterized by a passion for also:byCOLLINS DICTIONARY. and selling realCOLLINS estate, etc., for theCodepreciation initially of part of the urban web, in doi:10.1016/j.ijforecast.2009.05.013 10th edit. Wil. SONS AND Ltd. London 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification Royal Bank of Scotland, Parmalat or Royal Ahold (in free forecasts are the exception rather than the rule— Europe); or the practical collapse of the entire Iceland and forecasting errors are of no serious consequence, Concerns economy? In finance, who predicted the demise of thanks to the “thin-tailedness” of the deviations. S. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

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LTCM and Amaranth, or the hundreds of mutual and Consider flipping a coin 10 times; how many heads hedge funds that close down every year after incurring will appear? In this game there is no certainty about George-Sp. C. ATHANASOPOULOS huge losses? And these are just the tip of the iceberg. By Mr. the outcome, which can vary anywhere from 0 to 10. University, Graduate Design, Student, However, even withSchool the most of elementary knowledge of In the great majority of situations,Harvard predictions probability, the best forecast for the number of heads are never accurate. As is mentioned by Orrell and By Mr. George-Sp. C. ATHANASSOPOULOS Architect is 5, the Student most likelyof outcome, which isofalso the average McSharry (2009), the exception is with mechanical the School Architecture of all possible ones. It is possible to work out the systems in physics and engineering. The predictability Technical University ofthat Crete chance of getting exactly five heads is 0.246, or to of practically all complex systems affecting our lives is compute the corresponding probability for any other low, while1. theIntroductory uncertainty surrounding our predictions approach: Defining the concept number. cannot be reliably assessed. Perpetual calendars in 1. Introductory approach: Defining the concept (444 BC - 370 BC, Athens), the ancient philosopher, handheld ANTISTHENIS, devices, including watches, can showGreek the The distribution of errors, when a coin is flipped ANTISTHENIS, the ancient Greek philosopher, BCis -“principle”: BC,is Athens), exact among rise and set of thewise sun and the moon,he as left well us, he 10 established times and the (444 forecast 5370 heads, shown in other heritage a great the as theacquisition phases of the moon, up to the year 2099 and Fig. 1, together with the actual results of 10,000 among other wise heritage leftthe us,definition he established a greatof“principle”: the of knowledge startshe with of the content concepts. beyond.acquisition It is impressive such small starts deviceswith can thesimulations. The fit between the theoretical and actual of that knowledge definition the content of concepts. Based, therefore, on this “principle” in a first, if of not final, approach, the term provide highly accurate1 forecasts. For instance, they results is remarkable, signifying that uncertainty can Based, therefore, on this “principle” is inassessed a first,correctly if (in notthe final,flipping approach, the term (andinurban indicated of Planning) (or predictgentrification that on April 23, 2013, Greece:gentrification)be whenarea a coin 10 times. 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various Games of chance like flipping coins, tossing The sun will rise at 5:41 and set at 7:07 Sociology as well), as the “refining” of a city the removal from have this,an (inextremely various dice, area, or spinning roulette wheels of rise social groups, Theways), moon will at 4:44 and set usually at 3:55 of low-income and the placement there of artists, nice property: the events are independent, while the ways), of social groups, usually of low-income and the placement there of artists, operation of will art be galleries, etc. However this “change”, regardless of Thethe phase of the moon more thanrestaurants, 3/4 full, probability of success or“change”, failure is constant over allof the operation of art galleries, restaurants, etc. However this regardless or whatever 3 days from full moon.consequences has, results also rising of land prices (and the other trials. These two conditions allow us to calculate both whatever other consequences has, results also rising of land prices (and the potential speculation). These forecastsrelative are remarkable, as they concern the best forecast and the uncertainty associated with potential relative speculation). so many The years term into the future, and it isispractically Moreover, number gentrification found at firstvarious in theoccurrences. UK in early 1960swhen andn,it the refers to certainthe thatthen they term will begentrification perfectly accurate so many atpeople of trials, large,in the central limit theorem applies, The found first in the UK early 1960s and itareas refers observed trend ofiswealthy toisbuy property in poor ofto years from Theobserved same feelingtrend of awe isoffelt when guaranteeing that the distribution the mean, thenow. then wealthy people to there buy property in around poor areas London, upgrade them, stay themselves sometimes and thus old residents areof a spaceship arrives at its exact destination after many the most likely forecast, can be approximated by a London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. years of traveling through space, when a missile hits its normal curve, knowing that the larger the value of indirectly “squeezed”. A description of this phenomenon work of Sociologist precise being target thousands of kilometers away, or when is included n the betterin thethe approximation. Even when a Ruth coin is Abridge description ofperiod, this phenomenon istossed included inwere the=recorded work ofdistribution Sociologist Ruth a suspension spanning 2000 m can withstand a 10 times (n 10), the errors, GLASS at the same while similar situations in otherofmajor strongcities earthquake, as predicted in its specifications. with a forecast of 5, can be approximated pretty well GLASS at the same period, while similar situations were recorded in other major in Western countries, by other Researchers. Physics andinengineering have achievedbyamazing with a normal distribution, as can be seen in Fig. 1. cities Western countries, other Researchers. Since then, the issue has preoccupied several scholars and for its more successes in predicting future outcomes. By identifyWith celestial bodies and physical law relationSince then, the issue has preoccupied several below, scholars andthe for various its more comprehensive approach are being summarized from ing exact patterns and precise relationships, they can ships, we can achieve near-perfect predictions. With comprehensive approach are being summarized below, from the interpretations of the the extrapolate or interpolate them, to phenomenon achieve perfect, er-of gentrification, games of chance, wefollowing: know that there is no various certainty, of the like phenomenon the following: ror freeinterpretations forecasts. These patterns, the orbits of of we can out the most appropriate forecasts In a sense, the phenomenon is due togentrification, abut trend of figure a new category of social groups celestial objects, or relationships like those involvand estimate precisely the uncertainty involved. In the to “return” to the city, leaving the purlieus for several reasons: high costs in money ing gravity, can be expressed with exact mathematigreat majority of real life situations, however, there and time to then travel fromforthe purlieus where work lackforecast, of the cal models that can be used forecasting theto downtown, is always doubt as to whichplace is theis, “best” term from Sociologist GLASS, 1912-1940. Ruth search GLASS wasbetter born sense ofThe safety atcomes the distributed outside town for positions of1.the sun and the moon on April 23, residencies 2013, Ruthand, even worse, the centres, uncertainty surrounding a fore-in Berlin, where she made her first studies. In 1932 she published an important study entitled: or firing a missileoftohealth, hit a desired target thousands of cast cannot be heart assessed, reasons. First, in services education, entertainment “at the offor thethree city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for kilometers away. The models used make no significant most cases, errors areaccess not independent of oneetc. another; lower living cost of, “withdrawal” from private car easier to markets, studies and research in Geneva, Prague, London and New York she came back to London, where errors, even though they are simple and can often be their variance is not constant, while their distribution in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the isto due anormal systematic and programmed into hand-held cannot her be assured follow aHer curve—which University College devices. of London, where she continued social research. public action and long-term informal effort by organized groups, manufacturers, brokers of buying Predictions involving celestial bodies physicalfor justice. meansSee thatalso: the variance itselfENGLISH will be either intractable her work are characterized byand a passion COLLINS DICTIONARY. and selling real estate, for theCo depreciation initially ofofpart of the urban in law type relationships that result inetc., near-perfect, error or a poor indicator potential errors, what web, has been 10th edit. Wil. COLLINS SONS AND Ltd. London 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification Concerns S. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

By Mr. George-Sp. C. ATHANASOPOULOS Harvard University, Graduate School of Design, Student, By Mr. George-Sp. C. ATHANASSOPOULOS Architect Student of the School of Architecture Technical University of Crete

1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Fig. 1. assuming 5 heads a coin is flipped times (10,000from replications). Sociology as well), asThe theerros “refining” of when a city area, the10removal this, (in various Sociology as well), as the “refining” of a city area, fromthere this, of (inartists, various ways), of social groups, usually of low-income andthe theremoval placement called “wildofrandomness” by Mandelbrot (1963). Secinformation from empirical studies and three concrete ways), social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However this “change”, regardless of ond, there is always the chance of highly unlikely or examples, where ample data are available. the operation ofconsequences art galleries, restaurants, etc.also However regardless whatever other has, risingthis of “change”, land prices (and theof totally unexpected occurrences materializing — results and whatever consequences has, results2.1.also land pricespatterns (and the potential relative speculation). these can play aother large role (Taleb, 2007). Third, there Therising accuracyof when forecasting potential relative speculation). is a The severeterm problem outside of artificial setups,atsuch gentrification is found first in the UK in early 1960s and it refers to as games: is not observable, and it is quite Thebuy M-Competitions provided abundant Theprobability term gentrification found atpeople first in the UK in early 1960s and itareas refers the then observed trend ofiswealthy to property inhave poor ofto uncertain which probabilistictrend model to use. information the accuracy of all major timeof series the then observed of wealthy sometimes people to there buyabout property in poor areas London, upgrade them, stay themselves and thus old residents are In addition, we must remember that we do not foreforecasting methods aimed at predicting patterns. London, upgrade them, stay there and thus old residents are being cast for indirectly the sake of “squeezed”. forecasting, but themselves for some spe- sometimes Table 1 lists the overall average accuracies for all being indirectly “squeezed”. cific purpose, so we must realize that some forecast A description of this phenomenon is included in the workfor of the Sociologist forecasting horizons 4004 series Ruth used in the errors candescription cause harm orof missed whileis situations A this opportunities, phenomenon included inwere the recorded work of Sociologist Ruth M-Competition (Makridakis al., 1982) and the GLASS at the same period, while similar inetother major others can beat benign. So to us, any analysis ofsimilar fore- situations M3-Competition (Makridakis & Hibon, 2000). The GLASS the same period, while were recorded in other major cities in Western countries, by other Researchers. casting needs to take the practical dimension into actable includes five methods. Na¨ıve 1 is a simple, cities in Western countries, by other Researchers. Since then, the issue has errors preoccupied several scholars and for its more count: both the consequences of forecast and the readily available benchmark. Its forecasts for all Since then, the issue has preoccupied several scholars andthe for various its more fragility and reliability of predictions. In the case ofsummarized comprehensive approach are being horizons up below, to 18 arefrom the latest available value. comprehensive approach are being summarized below, from the various low reliability, we need to know what to do, dependinterpretations of the phenomenon of gentrification, thethefollowing: Na¨ıve 2 is same as Na¨ıve 1 except that the ing on the potential losses and opportunities involved. interpretations the phenomenon thecategory following: forecasts are appropriately for each In a sense, theof phenomenon is dueof togentrification, a trend of a new of seasonalized social groups horizon. Single exponential smoothing to “return” to the city, leaving the purlieus forforecasting several reasons: high costs in money is a simple method that averages the most recent 2. The accuracy and uncertainty forecasting and time to travel from theinpurlieus to downtown, where work place to is, the lacklatest of the values, giving more weight ones, in 1.of The term from Ruth GLASS, Ruth search GLASS wasbetter born in sense safety atcomes the distributed residencies outside centres, for order 1912-1940. to town eliminate randomness. Dampen exponential This section examines each Sociologist of two distinct Berlin, where she made her first studies. In 1932 smoothing she published an important study entitled: is similar to single, that it first issues associated with forecasting: theentertainment accuracy of services of health, education, “at the heart of the city”, except (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for smooths the most recenttotrend in the data to remove predictions and cost the uncertainty surrounding from them. private In lower living of, “withdrawal” car easier access markets, etc. studies and research in Geneva, Prague, London and New York she came back to London, where randomness and then extrapolates and dampens, as doing so, it distinguishes three types of predictions: in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the is due aa systematic and itsher names suchHer smoothed trend.and Single (a)University those involving (b)where those she utilizing College patterns, of London, continued socialimplies, research. public action long-term informal effort by organized groups, manufacturers, brokers of buying smoothing was found to be highly accurate in the relationships, and (c) those based primarily on human her work are characterized by a passion for justice. See also: COLLINS ENGLISH DICTIONARY. and selling real estate, theCodepreciation initially of part of the urban web,was in one and WIKIPEDIA: M3-Competitions, while dampen judgment. Each ofCOLLINS these threeetc., willfor be covered using 10th edit. Wil. SONS AND Ltd. LondonM2009. The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually 252111 11

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Table 1 MAPEa (average absolute percentage error) of various methods and percentage improvements. MAPEs: Forecasting horizons 1st

Na¨ıve1 Na¨ıve2 Single exponential smoothing Dampen exponential smoothing The Box–Jenkins methodology to ARIMA models

6th

18th

Improvement % Improvement in Avg. MAPE: (in Avg. MAPE) Avg. MAPE over Na¨ıve2 Single Dampen Box–Jenkins (1–18 horizons) Na¨ ıve1 Mr. George-Sp. over over over over By C. ATHANASOPOULOS Na¨ıve1 Na¨ıve2 Single Dampen

Harvard University, Graduate School of Design, Student, By Mr. George-Sp. C. ATHANASSOPOULOS Architect 1.9% 11.6% Student of6.4% the School of Architecture 2.9% Technical University of Crete

11.7% 18.9% 24.6% 17.9% 10.2% 16.9% 22.1% 16.0% 9.3% 16.1% 21.1% 15.0% 8.7%

15.0% 19.2% 13.6%

4.3%

8.1%

1. Introductory approach: Defining the concept 9.2% 14.9% 19.8% 14.2% 3.7% −2.5% 1. Introductory approach: Defining the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancient Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the a All MAPEs and % improvements are symmetric; that is, the divisor is: (Method1 – Method2)/(0.5∗Method1 + 0.5∗Method2). among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with thein definition ofseasonality the content of concepts. Based, therefore, “principle” a first, final, approach, theis term of the best methods in each of on thesethis competitions. 8.1%, on topifofnot and randomness, due to 1 (and urban therefore, on this “principle” inindicated a first, if (in notwhich final, approach, the term gentrification) is the area of Planning) (or gentrification dampen smoothing, eliminates the randomness Finally, theBased, Box–Jenkins methodology with ARIMA 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification in the most recent trend (we canthis, call (in this various trend the models, a statistically sophisticated method that Sociology as well), as the “refining” of a city area, the removal from momentum ofthe the series). Finally, the Box–Jenkins identifies and fits most appropriate autoregressive Sociology as well), as the “refining” of a city area, removal fromthere this, (inartists, various ways), of the social groups, usually of low-income andthe placement of method isand less the accurate than dampen smoothing by and/or ways), moving average model to the usually data, was of lesslow-income of social groups, placement there of artists, the operation of art galleries, restaurants, 0.6%, etc. However this “change”, regardless or, in relative terms, has a decrease of 2.5%of in accurate overall than dampen smoothing. the operation ofconsequences artofgalleries, restaurants, etc.also However this regardless whatever other has, results risingaccuracy. of “change”, land prices (and theof overall forecasting Table 1 shows the MAPEs these five methods whatever other consequences also rising of land prices (and the As dampen smoothing cannot predict turning potential relative for forecasting horizons 1, 6speculation). and 18, as well as has, the results points, we can assume that the Box–Jenkins does not potential relative speculation). overall average of all gentrification 18 forecasting horizons. Theat first in the UK in early 1960s and it refers to The term is found either, as it UK is less accurate dampen. addition,to forecasting errorsterm start atgentrification aroundtrend 10% for period atpeople The iswealthy found first in the early than 1960s and itIn refers the then observed ofone to buy in property in poor areas of dampen smoothing is considerably more accurate ahead forecasts, and almost double for 18 periods the then observed trend of wealthy sometimes people to buy property in poor areas of London, upgrade them, stay themselves there and thus old residents are than Holt’s exponential smoothing (not shown in ahead. These huge errors are typical of what can be London, upgrade them, stay themselves sometimes there and thus old residents are Table 1), which extrapolates the most recent smoothed being indirectly “squeezed”. expected when predicting series similar to those of the indirectly(the “squeezed”. trend, without finding indicates that, M- andbeing M3-Competitions consisting of is included A description ofmajority this phenomenon in dampening. the workThis of Sociologist Ruth onincluded average, in trends do not of continue uninterrupted, A description of this phenomenon is the work Sociologist Ruth economic, financial and business series). Table 1 also GLASS at the same period, while similarand situations were recorded in other Cyclical major should not,were therefore, be extrapolated. shows the improvements MAPE period, of the fourwhile GLASS at thein same situations recorded in other major cities in Western countries, by methods othersimilar Researchers. turns, for instance, reverse established trends, with over Na¨ ıve 1, in which was used as a benchmark. For Researchers. cities Western countries, by other Since several scholars its more the consequence of huge and errors for if such trends instance, Na¨ ıve 2 then, is 1.9% the moreissue accuratehas thanpreoccupied Na¨ıve Since then, the issue has preoccupied several scholars and for its more are extrapolated assuming that they will continue comprehensive approach are being summarized below, from the various 1, a relative improvement of 11.6%, while dampen uninterrupted. comprehensive approach summarized from the various smoothing is 4.3% moreof accurate than Na¨ıare ve 1, being aof gentrification, interpretations the phenomenon thebelow, following: of the phenomenon thecategory following: relativeinterpretations improvement ofthe 27.2%. In a sense, phenomenon is dueof togentrification, a2.2. trend a new of social groups The of uncertainty when forecasting patterns The right part of Table 1 provides information to “return” to the city, leaving the purlieus for several reasons: high costs in money about the source of the improvements in MAPE. As What is the uncertainty in the MAPEs shown in anddifference time tobetween travel Na¨ from where work place is, lack of the the only ıve 1the andpurlieus Na¨ıve 2 isto downtown, Table 1? Firstly, uncertainty increases together with 1.of The term comes from GLASS, 1912-1940. Ruth GLASS was born in sense safety the distributed residencies outside town centres, search that the latter captures theat seasonality in Sociologist the data, this Ruththe forecasting horizon. Secondly, suchfor an better increase Berlin, where she made her first studies. In 1932 she published an important study entitled: meansservices that the 11.6% improvement (the biggest of all) is bigger postulated However, of health, education, entertainment “atthan thethat heart of thetheoretically. city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for brought by Na¨living ıve 2 is cost due toof, predicting the seasonality it has been impossible to establish the distribution of lower “withdrawal” from private car easier access to markets, etc.where studies and research in Geneva, Prague, London and New York she came back to London, in the 4004 series. An additional improvement of forecasting errors in a fashion similar to that shown in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the isasdue a systematic and 6.4% comes fromCollege single of exponential smoothing, in Fig. her 1 orsocial Table 1, the number of observations in University London, where she continued research. Her public action and long-term informal effort by organized groups, manufacturers, brokers of buying which averages recent values order tofor justice. the series the COLLINS M-Competitions is notDICTIONARY. large enough. her workthe aremost characterized by ainpassion See in also: ENGLISH and selling realCOLLINS estate, for theCodepreciation initially part of the urban web, in eliminate random noise. The finaletc., improvement of For this2009. reason,WIKIPEDIA: weof will demonstrate theEncyclopedia: uncertainty in 10th edit. Wil. SONS AND Ltd. London The Free G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various Fig. 2. Predicted and theoretical number of rainy days. Sociology as well), as the “refining” of a city area, fromthere this, of (inartists, various ways), of social groups, usually of low-income andthe theremoval placement ways), of social groups, usually of low-income and the placement there of artists, forecasting by using four long series, allowing us to of the temperatures for all 108 years of of data, or the operation of art galleries, restaurants, etc. However this “change”, regardless ◦ C. look at the distributions of forecasting errors. 3.945 the operation of art galleries, restaurants, etc. However this “change”, regardless whatever other consequences has, results also rising of land prices (and theof However, it is of clear that the actual (and temperature Rainfall data other from January 1, 1971 to Mayhas, 6, 2008 whatever consequences results also rising land prices the on potential speculation). 1/1/2013 will, in all likelihood, be different from this (n = 13,648)relative in Amsterdam show that the chance of potential relative speculation). at first in the UKAn inidea early 1960s anderrors it refers to average. of the possible or uncertainty rain The on anyterm givengentrification day is very close is to found that of flipping The term atpeople first inaround the UK earlyprediction 1960s and refers this in average can it be inferred athe cointhen (0.506, to gentrification be precise). itfound rains more observed trendSince ofiswealthy to buy property in poor areas oftofrom Fig.to 4, there whichproperty shows the 108 ifareas we use 3.945, during someupgrade periods than during (i.e. events the then observed trend of wealthy people buy in errors poor London, them, stayothers themselves sometimes and thus old residents areof the average for January 1, as old the forecast. These errors areLondon, not independent), we them, can usestay Na¨ıvethemselves 1 to improve sometimes upgrade there and thus residents are being indirectly “squeezed”. vary from −13 to 8 degrees, with most of them being our ability to forecast. By doing so, we increase the being indirectly “squeezed”. A description this phenomenon is included in 7the of The Sociologist Ruth problem with Fig. 4, between andwork 11 ◦ C. probability of correctlyofpredicting rain from 0.506, A description ofperiod, thisindependent phenomenon included work of Sociologist Ruth GLASSthat at the while similar were in other major however,in isthe thatrecorded the distribution of errors does not assuming rainysame days are of eachis situations GLASS atFig. the2same period, recorded inmay other seem to bewere well behaved. This be major because we other, toin 0.694. shows the theoretical andsimilar actual situations cities Western countries, bywhile other Researchers. do not have enough data (a problem with most real forecasting errors using countries, Na¨ıve 1. Theby fit other betweenResearchers. the cities in Western Since then, the issue has preoccupied several scholars and for its more life series) orscholars because the and actual for distribution of errors theoretical andthen, actual errors is remarkable, indicating Since the issue has preoccupied several its more comprehensive approach being theThus, various is not normalbelow, or even from symmetric. we can say that we can estimate the uncertaintyare of the Na¨ıvesummarized comprehensive approach are being summarized below, from the various of the phenomenon gentrification, thelikely following: that our most prediction is 3.945 degrees, but it 1interpretations model with a high degree of reliability of when interpretations the phenomenon following: is difficult tothe specify the range of uncertainty using theoretical estimates. It seems thatof Inthe a sense, theof phenomenon is due toingentrification, a trend of a new category of social groupsin this example with any degree of confidence. binary forecasting situations, such as rain or no rain, to “return” to the city, leaving the purlieus for several reasons: high costs in money The number of forecasting errors increases signifiuncertainty can be estimated reliably. and time to travel from the purlieus to downtown, where work place is, lack of the cantly when we make short term predictions, like the Fig. 3 shows the average daily temperatures in term comes from 1912-1940. Ruth GLASS was born in sense1. ofThe safety thethedistributed outside town centres, for better temperature tomorrow, andsearch use Na¨ıve 1 as the forecast Paris for each dayat of year, Sociologist using residencies data Ruth from GLASS, Berlin, where she made her first studies. In 1932 she published an important study entitled: (meteorologists the accuracy of predictJanuary 1, of 1900 to December 31, 2007. Fig. 3 services health, education, entertainment “at the heartcan ofimprove the city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for ing theeasier weatheraccess over that of Na¨ıve 1 for up to three shows a living smooth cost pattern, with winter days having the lower of, “withdrawal” from private car to markets, etc. studies and research in Geneva, Prague, London and New York she came back to London, where days ahead). If weshe Na¨ıve 1, teacher the average error is lowest temperatures and summer days the highest in According 1943 she published studies regarding cityphenomenon planning. In 1950 in the to another approach, the is that dueuse tobecame a1systematic and zero, meaning Na¨ıve is an unbiased forecastones, as expected. Having identified and she estimated University College of London, where continued her social research. Her public action and long-term informal by organized groups, manufacturers, brokers ofofbuying with a standard deviation 2.71 degrees this pattern, the effort best forecast suggested herseasonal work are characterized by a passion for by justice.ing Seemodel, also: COLLINS ENGLISH DICTIONARY. and selling real estate, etc., for the depreciation initially of part of the urban in The a range of errors from to 11web, degrees. meteorologists for, COLLINS say, January 1, 2013, is the 10th edit. Wil. SONS AND Coaverage Ltd. Londonand 2009. WIKIPEDIA: The −11.2 Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually 252113 11

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1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as Fig. the3.“refining” of a city area, the removal from this, (in various Average daily temperatures in Paris: 1900 to 2007. Sociology as well), as the “refining” of a city area, fromthere this, of (inartists, various ways), of social groups, usually of low-income andthe theremoval placement ways), of social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However this “change”, regardless of the operation of art galleries, restaurants, etc. However this “change”, regardless whatever other consequences has, results also rising of land prices (and theof whatever otherspeculation). consequences has, results also rising of land prices (and the potential relative potential relative speculation). The term gentrification is found at first in the UK in early 1960s and it refers to The term gentrification found atpeople first in the UK in early 1960s and itareas refersofto the then observed trend ofiswealthy to buy property in poor the then observed trend wealthy sometimes people to there buy property in poor areas London, upgrade them, stay of themselves and thus old residents areof London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. being indirectly “squeezed”. A description of this phenomenon is included in the work of Sociologist Ruth A description ofperiod, this phenomenon is situations included inwere the recorded work of Sociologist Ruth GLASS at the same while similar in other major GLASS at the same period, while similar situations were recorded in other major cities in Western countries, by other Researchers. cities in Western countries, bypreoccupied other Researchers. Since then, the issue has several scholars and for its more Since then, the issue has several below, scholars andthe for various its more comprehensive approach arepreoccupied being summarized from comprehensive approach are being summarized below, from the various interpretations of the phenomenon of gentrification, the following: interpretations the phenomenon thecategory following: In a sense, theof phenomenon is dueof togentrification, a trend of a new of social groups to “return” to the city, leaving the purlieus for several reasons: high costs in money and time to travel from the purlieus to downtown, where work place is, lack of the term comes from Sociologist Ruth GLASS, 1912-1940. Ruth search GLASS for wasbetter born in sense1.ofThe safety thefrom distributed residencies town1st: centres, Fig. 4.at Errors the mean in daily temperatures (inoutside Celsius) on January 1900–2007. Berlin, where she made her first studies. In 1932 she published an important study entitled: services of health, education, entertainment “at the heart of the city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for the error distribution are muchmarkets, fatter thanetc. if they distribution ofliving these errors in Fig. 5, superlower cost is of,shown “withdrawal” from private access studies and research in Geneva, Prague, London and car Neweasier York she came to back to London, where were following a normal curve. For example, there imposedinon1943 a normal curve. she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the According to another approach, the is due a systematic and TwoUniversity observationsCollege come from Fig. 5. where First, there are 14 her errors of temperature less than −8.67 degrees, of London, she continued social research. Her public action and long-term informal effort by organized groups, manufacturers, brokers of buying are more errors the characterized middle of the distribution thanfor justice. corresponding toCOLLINS more than 4ENGLISH standard deviations from her workinare by a passion See also: DICTIONARY. and selling realCOLLINS estate, etc., for the depreciation initially part of the urban web, in postulated by the normal curve. Second, the tails of the mean. ThisWIKIPEDIA: is aof practical impossibility if the actual 10th edit. Wil. SONS AND Co Ltd. London 2009. The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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Table 2 DJIA 1900–2000: Worst-best daily returns.

1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various Sociology as well), as the “refining” of a city area, fromthere this, of (inartists, various ways), of social groups, usually of low-income andthe theremoval placement ways), of social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However this “change”, regardless of Fig. 6 shows the same information as Fig. 5, away from the mean such errors correspond to the operation of art galleries, restaurants, etc. However this “change”, regardless whatever other consequences has, results also rising of land prices (and (they theof except whatever that it refers to the values of the DJIA when range from 6.4rising to 21.2 standard deviations). other consequences has, results also of land prices Such (andlarge the potential relative speculation). Na¨ıve 1 is used as the forecasting model. The data errors could not have occurred in many billions of potential relative speculation). The term is found in the UK inpart early it refers to (n = 29,339) cover gentrification the same period as the Parisat first years if they were of a1960s normaland distribution. The term found firstThe in the UK in early 1960s and itinrefers to the then observed ofiswealthy to buy property in poor temperatures, January 1,gentrification 1900 totrend December 31, 2007 atpeople fact that the distribution of errors areas Fig. 6of is the then observed trend of wealthy people to buy property in poor areas of (thereLondon, are fewer observations because the stock market upgrade them, stay themselves sometimes there and thus old residents are much more exaggerated than that of Fig. 5 is due to is not being open during weekends and holidays). actual London, upgrade them, stayThe themselves sometimes there and thus residents are the human ability to influence theold DJIA, which is not indirectly “squeezed”. distribution of indirectly Fig. 6 also does not follow a normal the case with temperatures. Such an ability, together being “squeezed”. description thishigher phenomenon in the work of Sociologist Ruth curve. TheAmiddle values areof much than those is included the fact that humans overreact to both goodRuth and A description ofmore this values phenomenon iswith included inwere the work of Sociologist GLASS the while similar situations recorded in other major of Fig. 5, while at there aresame many period, outside bad news, increases the likelihood of large movements GLASS at the deviations same period, while situations were recorded in other major the limits of in ±4Western standard from mean.similar cities countries, bythe other Researchers. in the DJIA. There is no other way to explain the cities in Western countries, by other Researchers. For instance, there are 184 values below and above Since then, the issue has preoccupied several scholars and for 2,itsas more huge increases/decreases shown in Table it is not 4 standard deviations, whilethe thereissue should has not bepreoccupied any Since then, several scholars and for its more possible for the capitalization of all companies in the comprehensive approach are being summarized below, from the various such values if the distribution was indeed normal.2 DJIA to lose or gain such huge amounts in a single day comprehensive approach are being summarized below, from the various interpretations of the phenomenon of gentrification, the following: Table 2 further illustrates the long, fat tails of by real factors. interpretations of the thecategory following: In sense, phenomenon is due togentrification, a trend of a new of social groups the errors of aFig. 6 by the showing thephenomenon 15 smallest and of Another way to explain the differences between largesttoerrors and the number of standard deviations “return” to the city, leaving the purlieusthefortwo several reasons: high costs in money figures is that temperature is a physical and time to travel from the purlieus to downtown, wheresubject worktoplace is, lack the random variable, physical laws,ofwhile termat comes from Sociologist GLASS, 1912-1940. Ruth search GLASS wasvariables born in 2 Departure sense1.from ofThe safety residencies outside town for better markets arecentres, informational random normality isthe not distributed accurately measured by Ruthfinancial Berlin, where she made studies. she take an important study entitled: counting the number observations in her excessfirst of 4,entertainment 5, or 6 In 1932 that can any value restriction—there services ofofhealth, education, “at published the heart of without the city”, (possibly)for standard Youth deviationsUnemployment. (sigmas), but in looking at the contribution of The same year she leftare Germany and impediments after continuous movements no physical to the doubling of a large deviations to the total properties. For instance, the Argentine lower living cost of, “withdrawal” from private car easier access to markets, etc.where studies and research in Geneva, Prague, London and New York she came back to London, price. Although physical random variables can be noncurrency froze for a decade in the 1990s, then had a large jump. Its in 1943 she published studies regarding city planning. In 1950 sheto became teacher in the tothan another approach, is due a systematic and kurtosis wasAccording far more significant the Paris weather, although the phenomenon normalher owing to research. nonlinearities cascades, they University Collegein of London, where she social Herand public action and we onlylong-term had one single deviation excess of 4 sigmas. This is the continued informal effort by organized groups, manufacturers, brokers of buying still need obeyCOLLINS some structure, whileDICTIONARY. informational problem her with financial measurements that discard effect of afor justice. work are characterized by athepassion Seetoalso: ENGLISH and selling realCOLLINS estate, etc., for theCodepreciation initially ofnot part of the urban web, in random2009. variables do have any tangible constraint. single jump. 10th edit. Wil. SONS AND Ltd. London WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various Fig.“refining” 7. The daily forecasting errorsarea, for Citigroup, 1977–2008. Sociology as well), as the of a city the fromthere this, of (inartists, various ways), of social groups, usually of low-income and theremoval placement ways), of social groups, usually of low-income and the placement there of artists, theNon-normality operation gets of art galleries, restaurants, etc. However this “change”, regardless of worse where individual stocks Estimating relationships, like patterns, requires the operation of art galleries, restaurants, etc. However this “change”, regardless whatever has,bank results “averaging” also rising (andrandomness. theof of of theland data prices to eliminate are concerned,other as theconsequences recent experience with whatever other consequences has, resultsFig. also rising landofprices (andandthe 8 shows the of heights 1078 fathers sons,3 stocks has shown. For instance, the price of Citigroup potential relative speculation). potential relative speculation). as well as in theearly average of such a relationship passing dropped Septemberis9found and 17,at 2008, The34.7% termbetween gentrification first in the UK 1960s and it refers to the in middle of the data.and it refers to and then by 42.7% on the two days of Theincreased term gentrification found atpeople first inthrough the UK early 1960s the then observed trend ofiswealthy to buy property in poor areas of September 18 observed and 19. These are hugewealthy fluctuationspeopleThe most likely prediction the height the then trend to there buy property in for poor areasofofa son London, upgrade them, stay of themselves sometimes and thus old residents that are impossible to explain assuming independence whose father’s height is 180 cm is 178.59 are cm, given London, upgrade them, there and thus old residents are being indirectly “squeezed”. and well behaved errors (the stay meanthemselves daily return sometimes that the average relationship is: indirectly “squeezed”. ofbeing Citigroup is 0.044% standard deviation A description ofand thisthephenomenon is included in the work of Sociologist Ruth Height Son = 86.07 + 0.514(Height Father) is 2.318%). Therefore, the uncertainty surrounding A description of this phenomenon is situations included inwere the work of Sociologist Ruth GLASS at the same period, while similar recorded in other major = 178.59. (1) future returnsatofthe Citigroup cannot be while also assessed GLASS same period, similar situations were recorded in other major cities in Western countries, by other Researchers. either, as the distribution has long, fat tails (see cities in Western countries, bypreoccupied other Researchers. Clearly, it scholars is highly unlikely that its the more son’s height has several and for Fig. Since 7), and then, its errorsthe are issue both proportionally more will be exactly 178.59, the average postulated Since then, the issue has preoccupied several scholars and for its more by comprehensive approach being summarized below, from the various concentrated in the middle, and have are proportionally the relationship, as the from pairs ofthe heights of fathers comprehensive approach are being summarized below, various more extreme valuesofinthe comparison to those of of the interpretations phenomenon gentrification, following: and sons the fluctuate a great deal around the average DJIA shown in Fig. 6. interpretations the phenomenon the8.following: In a sense, theof phenomenon is dueof togentrification, a trend of ainnew of social groupsin the shown Fig. category The errors, or uncertainty, predictions depend upon the sizes of the errors and to “return” to the city, leaving the purlieus for several reasons: high costs in money 2.3. The accuracy and uncertainty when forecasting their distribution. These errors, shown Fig. 9, and time to travel from the purlieus to downtown, where work place is, lack ofinthe relationships fluctuate from aboutRuth −22.5 to +22.8 cm, with the 1. The term comes from Sociologist Ruth GLASS, 1912-1940. GLASS was born in sense of safety at the distributed residencies outside townbeing centres, search forand better big majority between −12.4 +12.4. Berlin, she made first studies. Into1932 she published an important study entitled: In There iswhere no health, equivalent of her the M-Competitions services of education, entertainment addition, “at the heart of theofcity”, (possibly) the distribution forecast errors seems Youth Unemployment. The same year she left Germany and after continuous movements formore provide us withcost information about the post-sample lower living of, “withdrawal” from private car easier access to markets, like a normal curve, although there are etc. more negative studies and research in Geneva, Prague, London and New York she came back to London, where forecasting accuracy of relationships. Instead, econoin According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the is due a systematic and to determine the she goodness metricians use College the R 2 value University of London, where continued her social research. brokers Her public action and long-term informal effort by organized groups, manufacturers, of buying ofher fit ofwork how are much better the average is justice. in 3 These areCOLLINS data introduced by Karl Pearson, a disciple of Sir characterized by arelationship passion for See also: ENGLISH DICTIONARY. and selling realmean estate, for theCodepreciation initially of part of the urban web, in Galton. comparison the (usedetc., as a benchmark). 10th edit.toWil. COLLINS SONS AND Ltd. LondonFrancis 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually 252117 11

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1. Introductory approach: Defining the concept 1. Introductory approach: the concept (444 BC - 370 BC, Athens), ANTISTHENIS, the ancientDefining Greek philosopher, ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) gentrification isarea, indicated (in thefrom areathis, of Planning) (or Fig. 10. Residual errors vs heights sons. Sociology as well), as the “refining” of a city theofremoval (in various Sociology as well), as the “refining” of a city area, the removal from this, (in various ways), of social groups, usually of low-income and the placement there of artists, less accurate than those of time series methods like (6.19 is the standard deviation of residuals). ways), of social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However “change”, Box–Jenkins.this Today, they are regardless only used by of governThus, the operation of art galleries, restaurants, etc. However this “change”, regardless whatever other consequences has, results mental also rising land prices (and theof for agenciesofand international organizations Height of Son = 178.59 ± 12.3. whatever otherspeculation). consequences has, resultssimulating also rising land (and the the policy of issues andprices better understanding potential relative consequences of these issues. Their predictive potential relative speculation). Even this simple example, ±12.3 cm indicates a in the UK in early 1960s and it refers toability Theinterm gentrification is found at first not UK considered of value Orrell & McSharry, lot of uncertainty in the prediction, which also suffers The term gentrification found atpeople first inisthe in early 1960s and itareas refers the then observed trend ofiswealthy to buy property in (see poor ofto 2009), as their limitations have been accepted by even from the fact that the distribution of errors is not the then observed trend of wealthy sometimes people to buy property in poor areas of London, upgrade them, stay themselves there and thus old residents are the econometricians themselves, who have concenentirely normal. In addition, there is another problem London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. trated their attention on developing more sophisticated that seriously affects uncertainty. If the errors are being indirectly “squeezed”. modelsinthat canwork better of fit the available data. plotted against the heights of thephenomenon sons (Fig. 10), they A description of this is included the Sociologist Ruth Taleb (2007) revisits the that major such conseA description of this phenomenon is included in the work of Sociologist Ruth show a strong correlation, implying that expression GLASS at the same period, while similar situations were recorded inidea other quences need to berecorded taken into account in decision mak(1)GLASS underestimates short heights and while overestimates at the same period, similar situations were in other major cities in Western countries, by other Researchers. ing. He shows that forecasting has a purpose, and it is tall ones. It is doubtful, therefore, that the forecast cities in Western countries, bypreoccupied other Researchers. Since the several and its more the purpose scholars that may need to befor modified when we are specified by then, expression (1)issue is the has best available for Since then, the issue has preoccupied several scholars and for its more comprehensive approach are being summarized below, from the various faced with large forecasting errors and huge levels of the heights of sons, while the uncertainty shown in comprehensive approach are being summarized below, from the various uncertaintythe thatfollowing: cannot be assessed reliably. expression (2) cannot estimated correctly, of as the interpretations ofbethe phenomenon gentrification, interpretations theFinally, phenomenon of thecategory following: errors highly correlated. thereisisdue an extra Inare a sense, theof phenomenon togentrification, a trend of a new of social groups 2.4. Judgmental forecasting and uncertainty problem when forecasting using relationships: the to “return” to the city, leaving the purlieus for several reasons: high costs in money values of the independent variables must, in the great and time to travel from(this theispurlieus downtown, wherefindings work place lackofofjudgmental the majority of cases, be predicted not the casetowith Empirical in theis,field term comes from Sociologist Ruth 1912-1940. Ruth search GLASS wasbetter born in is sense ofThe safety the distributed residencies outside town centres, for (1) as 1. the height ofat the father is known), adding an GLASS, psychology have shown that human judgment Berlin, she made first prediction. studies. In 1932 even she published study entitled: extra level where of to theher desired less accurate atimportant making predictions than simple services ofuncertainty health, education, entertainment “at the heartan of the city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for Forecasts from econometric models used to be popstatistical models. These findings goetc. back to the lower living cost of, “withdrawal” from private car easier access to markets, studies and research in Geneva, Prague, London and New York she came back to London, where ular, giving rise to an industry with revenues in the fifties with the work of psychologist Meehl (1954), in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the toofanother approach, the is some due astudies systematic and hundreds of millions dollars. Today, econometric who reviewed 20Her in psychology University College of London, where she continued her social research. public action and and long-term informal effort by organized groups, manufacturers, brokers of buying models haveare somewhat fallen out that the “statistical” of diagnosis her work characterized byofa fashion, passionas foremjustice.discovered See also: COLLINS ENGLISHmethod DICTIONARY. and selling realCOLLINS estate,that etc., theCodepreciation initially of part of the urban web, in pirical studies have showed theirfor predictions were superior to the traditional “clinical” approach. 10th edit. Wil. SONS AND Ltd. Londonwas 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually 252119 11

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification the funds that outperform the market for many years When Meehl published a small book about his in a row do so by the ability of their managers and research findings in 1954, it was greeted with outrage Concerns rather than because they happen to be lucky. So far by clinical psychologists all over the world, who S. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

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there is no empirical evidence that has conclusively felt professionally diminished and dismissed his proven that professional managers have consistently findings. Many subsequent studies, however, have George-Sp. C. ATHANASOPOULOS outperformed the broad market averages due to their confirmed Meehl’s original findings. A meta-analysis By Mr. own skills (and compensation). additionStudent, to the field Harvard University, Graduate School of In Design, by Grove, Zald, Lebow, Snitz, and Nelson (2000) of investments, Makridakis, Hogarth, and Gaba (2009) summarized the results of 136 studies comparing By Mr. George-Sp. C. ATHANASSOPOULOS Architect have concluded that in the areas of medicine, as well as clinical and statistical predictions across a wide range Student of the School of Architecture business, the predictive ability of doctors and business of environments. They concluded by stating: Technical University of Crete gurus is not better than simple benchmarks. These “We identified no systematic exceptions to the general findings raise the question of the value of experts: why Introductory approach: Defining the concept superiority1. (or at least material equivalence) of pay them to provide forecasts that are not better than 1. Introductory approach: Defining the concept (444 benchmarks mechanical prediction. It holds in general medicine, ANTISTHENIS, the ancient Greek philosopher, BC - 370 like BC,theAthens), chance, or than simple average or in mental health, in personality, and in education and ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), the latest available(444 value? among other wise heritage he left us, he established a great the training settings. It holds for medically trained judges question is,ahow well “principle”: human judgment among other wiseforheritage leftthe us,definition heAnother established great the acquisition ofItknowledge startshe with of the content ofcanconcepts. and for psychologists. holds inexperienced and assess future uncertainty? Empirical evidence has acquisition of knowledge starts with thein definition of the content of concepts. seasoned judges”. Based, therefore, on this “principle” a first, if not final, approach, the term shown that the ability of people to correctly assess 1 (and urban Based,oftherefore, this “principle” inindicated a first,isifeven notthe final, approach, the term gentrification) is (in area ofthat Planning) (or gentrification uncertainty worse than of accurately A large number people can beon wrong, and know 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification predicting future outcomes. evidence has that they can be wrong, brought by the comfort Sociology as well), asabout the “refining” of a city area, the removal fromSuch this, (in various shown that humans are overconfident of positive of a system. They continue their activities “because Sociology as well), as the “refining” of a city area, the removal from this, (in various ways), of social groups, usually of low-income and the placement there of artists, expectations, ignoring or downgrading other people doofit”. Theregroups, been no studies ways), social usually of low-income andwhile thethis placement there ofnegative artists, the operation of arthave galleries, restaurants, etc. However “change”, regardless of information. This means that when they are asked examining the notion of the diffusion of responsibility the operation of art galleries, restaurants, etc. However this “change”, regardless of whatever other consequences has, results also rising of land prices (and the to specify confidence intervals, they make them too in such problems of group error. whatever other consequences has, results also rising of land prices (and the relative speculation). tight, while not considering threatening possibilities Aspotential Goldstein and Gigerenzer (2009) and Wright potential relative like the consequences recessions, those to of and Goodwin (2009) point speculation). out, the isbiases andat first The term gentrification found in the UK in earlyof1960s and itorrefers the in current subprime and 1960s credit and crisis.itThis is to limitations of human judgment affect its to atpeople The term gentrification found first the UK in early refers the then observed trend ofisability wealthy to buy property in poor areas ofa serious problem, statistical methods also cannot make sound decisions when optimism influences its the then observed trend of wealthy people to there buyasproperty in poor areas London, upgrade them, stay themselves sometimes and thus old residents areof predict recessions and major financial crises, creating forecasts. In addition, it seems that the forecasts of London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. a vacuum resulting in surprises and financial hardships experts (Tetlock, 2005) are not more accurate than being indirectly “squeezed”. for large numbers of people, as nobody has provided A description this phenomenon those of other knowledgeableofpeople. Worse, Tetlock is included in the work of Sociologist Ruth with information to enable to consider A description thistophenomenon isthem included inwere the recorded work of Sociologist Ruth foundGLASS out that experts lessof likely change at thearesame period, whiletheir similar situations inthem other major thesituations full range of uncertainty associated withmajor their mindscities than non-experts, when new evidence appears GLASS at the same period, while similar were recorded in other in Western countries, by other Researchers. investments or other decisions and actions. disproving theirinbeliefs. cities Western countries, by other Researchers. Since then, the issue has preoccupied several scholars and for its more The strongest evidence against the predictive Since then, the issue has preoccupied several scholars andthe for its more comprehensive being summarized from value of human judgment approach comes from are the field 3. A summary of below, the eight papers of thisvarious issue comprehensive approach are being summarized below, from the various of investment, where a large number of empiricalof gentrification, the following: interpretations of the phenomenon interpretations of thethephenomenon thecategory following: comparisons proven, slightest is doubt, This introductory paper by Makridakis Taleb In have a sense, thebeyond phenomenon dueof togentrification, a trend of a new of socialand groups that the returns of professional managers are not better demonstrates the limited predictability and high level to “return” to the city, leaving the purlieus for several reasons: high costs in money than a random selection of stocks or bonds. As there of uncertainty in practically all important areas of our and time travel from purlieus work is, lackempirical of the are around 8500 to investment funds the in the USA, itto downtown, lives, and thewhere implications of place this. It presents termcan from Sociologist Ruthevidence GLASS, 1912-1940. Ruthpredictability, GLASS for wasbetter born sense1. ofThe safety atcomes the distributed residencies outside town search is possible that a fund beat, say, the S&P500, proving thiscentres, limited as wellin Berlin, where she made her first studies. In 1932 she published an important study entitled: for 13services years in aofrow. Is thiseducation, due to the ability of as examples involved health, entertainment “at theillustrating heart ofthe themajor city”,errors (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for its managers or to chance? If“withdrawal” we assume that from the private and thecar high levelsaccess of uncertainty that cannot be lower living cost of, easier to markets, etc. studies and research in Geneva, Prague, London and New York she came back to London, where probability of beating the S&P 500 each year is 50%, adequately assessed because the forecasting errors are in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the is due a systematic and not independent, andaction constant. then if University there were 8192 funds, it would where be possible College of London, she continued her social normally research.distributed Her public and long-term informal effort by organized groups, manufacturers, brokers of buying Finally, thealso: paperCOLLINS emphasizes the needDICTIONARY. to be rational for oneher of them beat the S&P500 by for a13passion years infor justice. worktoare characterized See ENGLISH selling realCOLLINS estate, theCo depreciation initially of of the urban web, in and realistic about ourpart expectations from forecasting, a rowand by pure chance. Thus, it isetc., not for obvious that 10th edit. Wil. SONS AND Ltd. London 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification and avoid the common illusion that predictions can be need to recognize that perfect individualized health accurate and that uncertainty can be assessed correctly. forecasting is not a realistic target in the foreseeable Concerns future, and we have to live with a considerable degree The second paper, by Orrell and McSharry, states 728

S. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

of residual uncertainty. that complex systems cannot be reduced to simple mathematical laws and be modeled appropriately. The sixth paper, by Fink, Lipatov and Konitzer, C. ATHANASOPOULOS The equations that attempt to represent them By are Mr. George-Sp. examines the accuracy and reliability of the diagnoses Harvard Graduate School of Design, only approximations to reality, and are oftenUniversity, highly made by general practitioners. TheyStudent, note that only sensitive to external influences and small changes 10% of the results of consultationsArchitect in primary care ByinMr. George-Sp. C. ATHANASSOPOULOS parameterization. Most of the time they fit past data canStudent be assigned to a School confirmedof diagnosis, while 50% of the Architecture well, but are not good for predictions. Consequently, remain “symptoms”, and 40% are classified as “named Technical University of Crete the paper offers suggestions for improving forecasting syndromes” (“picture of a disease”). In addition, they models by following whatapproach: is done in systems biology,the concept provide empirical evidence collected over the last 1. Introductory Defining integrating information from disparate sources in fifty years showing that less than 20% of the most 1. Introductory approach: the concept the ancientDefining Greek philosopher, (444 BC - 370for BC, Athens), orderANTISTHENIS, to achieve such improvements. frequent diagnoses account more than 80% of the ancient Greek philosopher, BC -“principle”: 370 BC,results Athens), the results of(444 consultations. Their prove TheANTISTHENIS, third paper,wise by Taleb, provides among other heritage heevidence left us,ofhe established a great the that primaryofcare a severe “black swan” the element the problemsother associated withheritage econometric models, and among wise leftthe us,definition he established a great acquisition of knowledge startshe with the has content of“principle”: concepts. in the vast majority of consultations. Some critical proposes a methodology to deal with such problems acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term cases involving “avoidable life-threatening dangerous by calibrating decisions, based on the nature of the 1 Based, therefore, on this “principle” in adevelopments” first, if (in notthe final, approach, the term urban gentrification) of Planning) (or brain gentrification such area as myocardial disturbance, forecast errors. Such(and a methodology classifies decision is indicated 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various bleeding and appendicitis may be masked by those payoffs as simple or complex, and randomness as thin Sociology as well), as “refining” of he a city area, the from this,disorders (inartists, various often symptoms of health ranked in or fat tailed. he the concentrates onlow-income what ways), of Consequently, social groups, usually of andvague theremoval placement there of the 20% of most frequent diagnoses. They calls the fourth quadrant (complex payoffs and fat tail ways), of social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However this “change”, regardlessconclude of proposing this that (1) primary care should no of longer randomness), and proposes solutions torestaurants, mitigate the etc.byHowever the operation ofconsequences art galleries, “change”, regardless whatever other has, results also rising of land prices (and the be defined only by “low prevalence” properties, but effects of possibly inaccurate forecasts based on the whatever other consequences has, resultsalso also rising of land prices (and(2) the potential relative speculation). by its black-swan-incidence-problem; at the nature of complex systems. potential relative speculation). levelUK of everyday diagnostic protocols The by Goldsteinisand Gigerenzer, Thefourth termpaper, gentrification found at first in the in earlypractice, 1960s and it refers to are make diagnoses more and Theevidence term gentrification found atpeople first innecessary the UKtoin early 1960s andreliable; itareas refers provides that some of the and frugal the then observed trend ofisfast wealthy to buy property in poor ofto(3) at the to levelbuy of epidemiology, a system ofareas classifications heuristics that observed people use intuitively are able to makepeople the then trend of wealthy property in poor of London, upgrade them, stay themselves sometimes there and thus old residents are is crucial for generating valid information by which forecasts that upgrade are as good as or stay betterthemselves than those of sometimes London, them, there and thus old residents are being indirectly “squeezed”. predictions of risks can be improved. knowledge-intensive procedures. By using research on indirectly “squeezed”. A description of ecological this phenomenon is included the work Ruth and thebeing adaptive toolbox and rationality, they Theinseventh paper,ofbySociologist Makridakis, Hogarth A description ofperiod, this phenomenon is situations included inwere the further work empirical of Sociologist Ruth demonstrate of using intuitive Gaba, provides evidence that accuGLASS atthethepower same whileheuristics similar recorded in other major for forecasting in various domains, including sports, rate forecasting in the economic and business world GLASS at the same period, while similar situations were recorded in other major cities in Western countries, by other Researchers. business, andWestern crime. is usually not possible, due to the huge uncertainty, cities in countries, by other Researchers. Since then, the issue has preoccupied as several scholars and for its more practically all economic and business activities are The fifth paper, by Ioannidis, provides a wealth Since then, the issue has preoccupied several scholars and for various its more comprehensive approach are being summarized below, subject to events whichfrom we are the unable to predict. The of empirical evidence that while biomedical research comprehensive approach are being summarized below, from the various interpretations ofamounts the phenomenon gentrification, the following: fact that forecasts can be inaccurate creates a serious is generating massive of information of about interpretations of the gentrification, following: dilemma forthe decision and policy makers. On the one potential factors for phenomenon health and is disease, few In aprognostic sense, the phenomenon dueof to a trend of a new category of social groups accepting the limits of forecasting accuracy imprognostic factors havecity, beenleaving robustly validated, and forhand, to “return” to the the purlieus several reasons: high costs in money plies being unable to assess the correctness of decifewer still have made a convincing difference in health and time to travel from the purlieus to downtown, where work place is, lack of sions and the surrounding uncertainty. On the the other outcomes or in prolonging life expectancy. For most The termat comes from Sociologist Ruth GLASS wasbetter born in sense1.of safety the distributed residencies outside town centres, search for hand,1912-1940. believing thatRuth accurate forecasts are possible diseases and outcomes, a considerable component of GLASS, Berlin, where she made her first studies. In 1932 she published an important study entitled: means succumbing the illusion control and expethe prognostic variance remains unknown, and may services of health, education, entertainment “at the heart ofto the city”,of(possibly) Youth Unemployment. The same year she left Germany and after continuous movements for riencing surprises, oftento with negative consequences. remain so in the cost foreseeable future. Ioannidisfrom suggests lower living of, “withdrawal” private car easier access markets, etc.where studies and research in Geneva, Prague, London and New York she came back to London, They suggest that the time has come for a new attitude that in order to improve studies medical regarding predictions,city a planning. in According 1943 she published In 1950 sheto became teacher in the to another approach, the phenomenon is due a systematic and towards dealing with the future that accepts ourand limited systematic approach to of theLondon, design, conduct, reporting, University College where she continued her social research. Her public action long-term informal effort by organized groups, manufacturers, brokers of buying ability to make predictions in the economic and replication, and clinical translation of prognostic her work are characterized by a passion for justice. See also: COLLINS ENGLISH DICTIONARY.busiand selling realCOLLINS estate, theCodepreciation initially of part of the urban web, in environment, while also providing a framework research is needed. Finally,etc., he for suggests that 10th edit. Wil. SONS AND Ltd.we Londonness 2009. WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification reasons than the accurate forecasting of future that allows decision and policy makers to face the temperatures. future — despite the inherent limitations of forecastConcerns The tenth paper, by the late David Freedman, ing and the huge uncertainty surrounding most futureS. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

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shows that model diagnostics have little power unoriented decisions. less alternative hypotheses can be narrowly defined. The eighth paper, by Wright and Goodwin, looks C. ATHANASOPOULOS For George-Sp. instance, independence of observations cannot at scenario planning as an aid to anticipation of the By Mr. be tested against general forms of dependence. This Harvard University, Graduate School of Design, Student, future under conditions of low predictability, and means that the basic C. assumptions in regression modGeorge-Sp. ATHANASSOPOULOS Architect examines its success in mitigating issues to do with By Mr. els cannot be inferred fromSchool the data.of The same is true Student of the Architecture inappropriate framing, cognitive and motivational with the proportionality assumption, in proportionalbias, and inappropriate attributions of causality. Technical University of Crete hazards models, which is not testable. SpecificaThey consider the advantages and limitations of tion error is a primary source of uncertainty in such planning and identify four potential principles 1. Introductory approach: Defining the concept forecasting, and such uncertainty is difficult to refor improvement: (1) challenging mental frames, 1. Introductory approach: Defining the concept (444 calibration, ANTISTHENIS, the (3) ancient Greek philosopher, BC - 370while BC,model-based Athens), solve without external (2) understanding human motivations, augmenting ANTISTHENIS, the ancient Greek philosopher, (444 BC -“principle”: 370 BC, Athens), causal inference is more problematic to the test. among other wise heritage he left aeven great scenario planning through adopting the approach of us, he established These problems decrease the value of our models among other wise heritage he leftthe us,definition he established a greatof“principle”: the crisis acquisition management, and (4) assessing the flexibility, of knowledge starts with of the content concepts. and increase the uncertainty of their predictions. acquisition of knowledge starts with definition of the content of concepts. diversity, and insurability of strategic options in a thein Based, therefore, on this “principle” aThefirst, if not final, approach, the term final paper of this issue, written by the structured option-against-scenario evaluation. 1 (and urban Based, therefore, on this “principle”editors, inindicated a first, if (in notthe final, approach, the term gentrification) is area ofissues Planning) (or gentrification is a summary of the major surrounding The gentrification ninth paper, by1 (and Green, Armstrong and urban gentrification) isarea, indicated (in area of Planning) (or forecasting, and also the puts forward a number of Sociology as well), as the “refining” of a city the removal from this, (in various Soon, proposes a no change, benchmark model for ideas aimed at a complex world where accurate Sociology as well), as the “refining” of a city area, the removal from this, (in various ways),temperatures of social groups, usually low-income and the placement there of artists, forecasting which they argue of is the predictions arethe not placement possible and there uncertainty ways), ofone, social groups, usually of low-income and of artists, operation art galleries, restaurants, etc. However this “change”,where regardless of most the appropriate asoftemperatures exhibit strong reigns. However, once we accept the inaccuracy of the operation of art galleries, restaurants, etc. However this “change”, regardless (cyclical) fluctuations and there is no obvious trend whatever other consequences has, results also the rising ofquestion land prices (and theof forecasting, critical is, how can we plan, over the past 800,000 years that Antarctic temperature whatever other consequences has, results also risinginvest of land pricesmanage (and our the potential relative speculation). formulate strategies, our savings, data from the ice-core record isspeculation). available. These data potential relative andUK in general make future-oriented decisions, The term gentrification is found at firsthealth, in the in early 1960s and it refers to also show that the temperature variations during the accepting that there are no crystal balls? is whereto The term gentrification iswealthy found atpeople first in the UK in early 1960s andThis itareas refers the then observed trend of to buy property in poor of late 1900s were not unusual. Moreover, a comparison the editorstobelieve much more andareas thinking the observed trend wealthy sometimes people buy that property ineffort poor London, upgrade them, themselves there and thus residents areof between the then ex ante projections ofstay the of benchmark is needed, and where they are old advancing a number London, upgrade them, stay themselves sometimes there and thus old residents are modelbeing and those made by the Intergovernmental indirectly “squeezed”. of proposals to avoid the negative consequences ◦ C-per-year were being indirectly “squeezed”. Panel on Climate Change at 0.03 involved while also profiting from the low levels of A description of this phenomenon is included in the work of Sociologist Ruth practically indistinguishable from one another in the predictability. A description of this phenomenon is included in the work of Sociologist Ruth GLASS at the same period, while similar situations were recorded in other major small sample of errors between 1992 through 2008.similar situations were recorded in other major GLASS at the same period, cities in Western countries, bywhile other The authors argue that the accuracy of forecasts fromResearchers. 4. The problemsscholars facing forecasters cities inisWestern countries, by other Researchers. Since then, the issue has preoccupied several and for its more the benchmark such that even perfect prediction Since then, the issue has preoccupied several scholars andthe for various its more wouldcomprehensive be unlikely to help policymakers getting approach inare being summarized below, from The forecasts of statistical models are “mechancomprehensive approach are being summarized below, from the various forecasts that are substantively accurate thanof gentrification, interpretations of themore phenomenon following: ical”, unable tothe predict changes and turning points, those from a no change, benchmark model. interpretations the phenomenon thecategory following: unable make predictions for social brand new situaIn a sense, theof phenomenon is dueof togentrification, aand trend oftoa new of groups Because global warming is an emotional issue, tions, or when there are limited amounts of data. These to “return” to the city, leaving the purlieus for several reasons: high costs in money the editors believe that whatever actions are taken to tasks require intelligence, knowledge and an ability to and time to travel fromcannot the purlieus work only place lack of the reverse environmental degradation be justifiedto downtown, learn which where are possessed by is, humans. Yet, as 1.of The from Sociologist GLASS, 1912-1940. Ruthare GLASS wasbetter born safety atcomes the distributed residencies outside town centres, search for on thesense accuracy ofterm predictions of mathematical or Ruthwe saw, judgmental forecasts less accurate thanin Berlin, where she it made studies. she published an important study entitled: statistical models. musther be first accepted that In 1932 the brainless, by statistical services ofInstead, health, education, entertainment “at themechanistic heart ofones the provided city”, (possibly) Youth Unemployment. Theand same year she left Germany and after continuous movements for accurate predictions are not possible uncertainty models. Forecasters find themselves betweenetc. Caryblower living cost of, “withdrawal” from private car easier access to markets, studies and research in Geneva, Prague, London and New York she came back to London, where cannot be reduced (a fact made obvious by the dis and Scylla. On the one hand, they understand the in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the is due a systematic and many and contradictory predictions concerning global limitations of the statistical models. On the other hand, University College of London, where she continued her social research. Her public action and long-term informal effort by organized groups, manufacturers, brokers of buying warming), whatever actions are taken to protectfor justice. their own cannot be trusted. The biggest adherand work are characterized by a passion Seejudgment also: COLLINS ENGLISH DICTIONARY. and selling realCOLLINS etc., for theCo depreciation initially of part of the web, in the environment beestate, justified based on other vantage2009. of statistical predictions isurban their objectivity, 10th edit.must Wil. SONS AND Ltd. London WIKIPEDIA: The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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730

Table 3 Values of daily statistics for DJIA and Paris temperatures for each decade from 1900 to 2008.

1. seems Introductory Defining daily temperatures, as they are very similar in the which to be moreapproach: important than the intelli-the concept 1. Introductory approach: Defining the concept gence, knowledge and ability of humans to Thephilosopher, decades 1900–1910 and- 1910–1920. Starting from the ANTISTHENIS, the ancient learn. Greek (444 BC 370 BC, Athens), problem with humans is that the they ancient suffer fromGreek incon- philosopher, decade 1920–1930 onwards, however, both the means ANTISTHENIS, (444 BC 370 BC, Athens), among other wise heritage he left us, he established a great “principle”: the sistency, wishful thinking and all sorts of biases that and the standard deviations of the percentage daily among other wise heritage he left us, he established a great “principle”: the acquisition of knowledge starts with the definition of the content of concepts. diminish the accuracy of their predictions. The biggest changes in the DJIA vary a great deal, from 0.001% acquisition of knowledge starts withis the definition the content of 1990s concepts. Based, “principle” a first, if of not approach, the challenge andtherefore, only solutionontothis the problem forin in the 1930s tofinal, 0.059% in the (thisterm means that 1 (and Based, on this inindicated a$10,000 first, if notthe final, approach, thewould term humans to findtherefore, ways to urban exploit their“principle” intelligence, is invested at the beginning of 1930 gentrification) (in area of Planning) (or have gentrification 1 (and knowledge and ability to as learn while avoiding their become by the endthis, of 1939, while the gentrification urban gentrification) indicated (in the area of Planning) (orsame Sociology as well), the “refining” of aincityisarea, the$10,334 removal from (in various consistencies, wishful thinking and“refining” biases. We believe amountthe invested at the from beginning of(in 1990 would have Sociology as well), as the of a city area, removal this, various ways), social groups, usually of low-incomegrown andtothe placement there of artists, that muchof work can be done in this direction. by the end of 1999). The differences ways), of groups, usually of limited low-income and $44,307 thethis placement there of artists, the operation of art galleries, restaurants, etc. However “change”, regardless ofwhich Below, we social summarize the problem of are equally large for the standard deviations, the operation of art galleries, restaurants, etc. However this “change”, regardless predictability highconsequences levels of uncertaintyhas, usingresults the whatever and other alsofrom rising ofinland prices (and theof range 0.65% the 1960s to 1.85% in the 1930s. daily values relative of other the DJIA and the Paris temperatures. whatever consequences has, resultsOnalso rising (andinthe the other hand,oftheland meanprices daily changes temperpotential speculation). The availability of fast speculation). computers and practically atures are in small, except possibly forrefers the 2000–2008 potential relative The term gentrification is found at first in the UK early 1960s and it to unlimited memory has allowed us to work with long period, when they increased to 0.005 of a degree. The term gentrification is found at first in the UK in early 1960s and it refers to In the then observed trend of wealthy people to buy property in poor areas of series and study how well they can forecast and addition, the standard deviations have remained pretty the then observed of wealthy people to there buy property in poor areas London, upgrade them, stay various themselves sometimes and thus old residents areof identify uncertainty. Table 3trend shows statistics much constant throughout all eleven decades. London, upgrade them, there and thus old residents are for for the daily % changes in the stay DJIAthemselves and the daily sometimes being indirectly “squeezed”. Table 3 conveys a clear message. Forecasting changes inindirectly Paris temperatures, for each decade from being “squeezed”. some series, like the DJIA, cannot be accurate, A description of this phenomenon is included in the work of Sociologist Ruthas the 1900 to (the 2000 toof2008 does not coveris included assumption of constancy of their patterns,major and possibly A2008 description thisperiod phenomenon inwere the work of Sociologist Ruth GLASS at the same while similar situations recorded in other the whole decade). Table period, 3 allows us to determine relationships, is violated. Thisin means thatmajor predicting GLASS at the same period, while similar situations were recorded other cities inwe Western countries, byuncertainty other Researchers. how well can forecast and assess for for the next decade, or any other forecasting horizon, in1910–1920, Western countries, bypreoccupied other thecities decade given the information forResearchers. the Since then, the issue has several scholars andinformation, for its more cannot be based on historical as both the decade 1900–1910, forthe the decade givensummarized Since then, issue 1920–1930 has several scholars and for its more comprehensive approach arepreoccupied being from the mean and thebelow, fluctuations around thevarious mean vary too thecomprehensive information for 1910–1920, and so on. approach are being summarized much fromthe onebelow, decade to from another.the Doesvarious the increase to interpretations of the phenomenon of gentrification, following: 0.005 changes in dailyofParis temperature interpretations the phenomenon gentrification, the following: In sense, theof phenomenon is due to a trend ofina the new category social groupsfor the 4.1. Theamean percentage change of the DJIA andof the period of 2000–2008 indicate global warming? This is average change in Paris temperature to “return” to the city, leaving the purlieus foraseveral reasons: high costs in money question we will not attempt to answer, as it has been and time to travel from the purlieus to downtown, where work is, lack theissue. dealt with in the paperplace by Green et al. of in this The mean percentage change in the DJIA for the termat from Sociologist Ruth 1912-1940. Ruth GLASS wasbetter born in like sense1.1900–1910 ofThe safety the distributed residencies outside town centres, search for However, the potential exists that even in series decade iscomes 0.019%. If such a change had GLASS, Berlin, where she made her first studies. In 1932 temperature she published an important study entitled: we have to worry about a possible change been used as forecasteducation, for the decadeentertainment 1910–1920, services ofthe health, “at the heart of the city”, (possibly) Youth Unemployment. The same year she left Germany andterm after continuous movements for incar the long trend. the results would haveof, been highly accurate. In adlower living cost “withdrawal” from private easier access markets, etc.where studies and research in Geneva, Prague, London and New York she came to back to London, Another technique for looking at differences is dition, the volatility in the daily percentage changes in According 1943 she published studies regarding cityphenomenon planning. In 1950 sheto became teacher in the to another approach, the is due a systematic and departures normality. the kurtosis from 1900–1910 wouldofhave been where an excellent preUniversity College London, she continued her socialfrom research. HerConsider public action and of long-term informal effort by organized groups, manufacturers, brokers of buying variables. TheENGLISH 5 largest DICTIONARY. observations in the dictor for 1910–1920. The same by is true with both her work are characterized a passion forthe justice.the Seetwo also: COLLINS and selling real estate, etc., for thechanges depreciation initially of part of the in For represent 3.6% ofurban theEncyclopedia: totalweb, kurtosis. means and theWil. standard deviations ofAND the 10th edit. COLLINS SONS Co Ltd. in Londontemperature 2009. WIKIPEDIA: The Free G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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GENTRIFICATION Definition, Types of Intervention, Definition, of intervention, ConcernsTypes of Gentrification the Dow Jones, the 5 largest observations represent close to normal with not too fat tails (the skew38% of the kurtosis (e.g., the kurtosis in the decade ness and kurtosis of the distribution were 0.33 and Concerns 1970–1980 is 1.89, while that of the following decade 1.89 respectively), while that of the 1980s was too S. Makridakis, N. Taleb / International Journal of Forecasting 25 (2009) 716–733

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tall in the middle (the kurtosis was 68.84, versus is an incredible 68.84—see Table 3). Furthermore, 1.89 in the 1970s) with considerable fat tails on both under aggregation (i.e., by taking longer observation C. ATHANASOPOULOS ends.George-Sp. Given the substantial differences in the distriintervals of 1 week, 1 fortnight, or 1 month), the By Mr. butions of changes, or errors, is it possible to talk Harvard University, Graduate School of Design, Student, kurtosis of the temperature drops, while that of the about assessing uncertainty in statistical models when stock market does not change. By Mr. George-Sp. C. ATHANASSOPOULOS Architect (a) the distributions normal,of even with series In real life, most series behave like the DJIA; Student ofare thenotSchool Architecture like temperatures; Technical (b) the means and standard in other words, humans can influence their patterns University ofdeviaCrete tions change substantially; and (c) the distributions or and affect the relationships involved by their actions errors are not constant? We believe that the answer is a and reactions. In such cases, forecasting is extremely 1. Introductory approach: Defining the concept strong no, which raises serious concerns about the redifficult or even impossible, as it involves predicting 1. Introductory approach: Defining the concept models ANTISTHENIS, the ancient Greek philosopher, BC 370 BC, alism of financial(444 that- assume thatAthens), uncertainty human behavior, something which is practically ANTISTHENIS, the ancient Greek philosopher, (444 BC -“principle”: 370are BC, can be assessed assuming that errors wellAthens), behaved, impossible. However, even with series he likeleft the us, he established among other wise heritage a great the with a zero mean, a constant variance, a stable temperature human intervention is also possible, among other wise heritage leftthe us,definition he established a greatof“principle”: the acquisition of knowledge startshe with of the content concepts. distriand independent errors. of concepts. although there is noofconsensus in predicting its thebution acquisition knowledge starts with definition of the content Based, therefore, on this “principle” in a first, if not final, approach, the term The big advantage of series like the DJIA and consequences. 1 (and urban Based, therefore, on this “principle”the inindicated a first, if (in notthe final, approach, the term gentrification) is area of Planning) (or gentrification Paris temperatures is the extremely large number 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification of available data points that allows us to extract Sociology as well), as the “refining” of a city area, the removal from this, (in various 4.2. The uncertainty in predicting changes in DJIA different types information, asof that shown Sociology as well), as the “refining” of a city area, the fromsuch this, (in various and Paris temperatures ways), of social groups, usually of low-income and theofremoval placement there artists, in Table and 3, which is based on there more of thanartists, ways), of social groups, usually of low-income the placement the operation of art galleries, restaurants, observations etc. However this “change”, regardless2500 of in the case of the DJIA, and 3650 for Having data since 1900 provides us with a unique the operation ofconsequences art galleries, restaurants, etc.also However this “change”, regardless of whatever other has, results rising of land prices (and the the temperatures. Real life series, however, seldom opportunity to break it into sub-periods and obtain whatever other consequences has, results also rising of land prices (and the exceed a few hundred observations at most, making usefulpotential insights byrelative examiningspeculation). their consistency (see potential relative speculation). it impossible to in construct to those Table 3), as we have already done for the mean, and weat first The term gentrification is found in the UK earlydistributions 1960s andsimilar it refers to of Table In such aearly case we are poor completely unable Thetheterm gentrification found first in the UK in 1960s and itareas refers can now uncertainty intrend these two series. The atpeople theassess then observed ofis wealthy to3. buy property in ofto to verify the assumptions required assure areas ourselves traditional to assessing uncertainty assumes theapproach then observed trend wealthy sometimes people to there buy property intopoor London, upgrade them, stay of themselves and thus old residents areof that there are not problems with the assessment normality and then constructs confidence intervals London, upgrade them, stay themselves sometimes there and thus old residents are being indirectly “squeezed”. of uncertainty. Finally, there is another even more around the mean. Such an approach cannot work for being indirectly “squeezed”. important assumption, that of also A description thisforphenomenon in the work ofindependence, Sociologistthat Ruth the percentage changes in theof DJIA three reasons. is included A description ofnot this phenomenon isfails included theand work of Sociologist Ruth to hold in true, negatively the First, GLASS the standard are constant; second, atdeviations the same period, while similar situations were recorded inaffects otherboth major task of forecasting andrecorded that of assessing uncertainty. the means also change substantially from one decade GLASS at the same period, while similar situations were in other major cities in Western countries, by other Researchers. For instance, it is interesting to note that between to another (seein Table 3); andcountries, finally, the distribution cities Western bypreoccupied other Researchers. Since then, the issue has several scholars for52.7% its more September 15 and December and 1, 2008, of the is not normal (see Fig. 6). Assessing the uncertainty Since then, the issue has preoccupied several scholars and for itsthan more comprehensive approach are being summarized below, from the various daily fluctuations in the DJIA were greater the in the changes in Paris temperatures does not suffer comprehensive approach are being summarized below, from the various mean ±3 (standard deviations). In the temperature of the phenomenon the following: from interpretations the first or second problem, as the means andof gentrification, fewer big concentrations extreme of the phenomenon the following: standardinterpretations deviations are the fairly constant. However, the of In a sense, phenomenon is due togentrification, achanges trend there of a are new category of socialofgroups values, but since 1977 we can observe that the distribution of changes is not quite normal (see Fig. 5), to “return” to the city, leaving the purlieusgreat for several reasons: high costs in money majority of such values are negative, again as there are a considerable number of extremely large and time to travel from the purlieus to downtown, where work place is, lack of the obliging us to question the independence of series like and small changes, while there are more values around 1.of The termat comes from Sociologist Ruthtemperatures, GLASS, 1912-1940. Ruth GLASS wasbetter bornbyin which centres, seem to be also influenced sense the distributed residencies outside town search for the mean than in safety a normal curve. Berlin, sheproblem made her first studies. In 1932 she published an important study entitled: non-random runs of higher and lower temperatures. There is an where additional when attempting services of health, education, entertainment “at the heart of the city”, (possibly) Youth Unemployment. The same year she left Germany and after continuous movements for to assess uncertainty. The distribution of changes lower living cost of, “withdrawal” from private car easier access to markets, etc.where studies and research in Geneva, Prague, London and New York she came back to London, also varies a great deal, as can bestudies seen inregarding Fig. 11. city5.planning. Conclusions in According 1943 she published In 1950 sheto became teacher in the to another approach, the phenomenon is due a systematic and Worse, University this is true not only inofthe DJIA data, but she also continued her social research. Her public action and College London, where long-term informal effort by organized groups, manufacturers, brokers of buying in the temperature data. In the 1970s, instance,for justice. Forecasting future is neither easy DICTIONARY. nor certain. At her work are characterized byfor a passion See also:the COLLINS ENGLISH and selling real estate, etc., for theCo depreciation initially ofseem partthat of the urban web,But in the distribution of Wil. the DJIA percentage changes was the same time,WIKIPEDIA: it may we have no choice. 10th edit. COLLINS SONS AND Ltd. London 2009. The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually

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1. Introductory approach: Defining the concept 1. Introductory approach: Defining the concept (444 BC - 370 BC, Athens), the ancient Greek philosopher, (a) ANTISTHENIS, The distribution of daily percentage changes in the DJIA in the (b) The distribution of daily percentage changes in the DJIA in the ANTISTHENIS, the ancient Greek philosopher, BC -“principle”: 370 BC, Athens), 1970s. 1980s. among other wise heritage he left us, he established(444 a great the among other wise heritage leftthe us,definition he established a greatof“principle”: acquisition of knowledge startshe with of the content concepts. the acquisition of knowledge starts with theindefinition the content of concepts. Based, therefore, on this “principle” a first, if of not final, approach, the term 1 (and urban Based, therefore, on this “principle” is inindicated a first, if (in notthe final, approach, the term gentrification) area of Planning) (or gentrification 1 (and urban gentrification) is indicated (in the area of Planning) (or gentrification Sociology as well), as the “refining” of a city area, the removal from this, (in various Sociology as well), as the “refining” of a city area, fromthere this, of (inartists, various ways), of social groups, usually of low-income andthe theremoval placement ways), of social groups, usually of low-income and the placement there of artists, the operation of art galleries, restaurants, etc. However this “change”, regardless of the operation of art galleries, restaurants, etc. However this “change”, regardless whatever other consequences has, results also rising of land prices (and theof whatever otherspeculation). consequences has, results also rising of land prices (and the potential relative potential relative speculation). The term gentrification is found at first in the UK in early 1960s and it refers to The term gentrification found atpeople first in the UK in early 1960s and itareas refersofto the then observed trend ofiswealthy to buy property in poor the then observed trend wealthy sometimes people to there buy property in poor areas London, upgrade them, stay of themselves and thus old residents areof London, upgrade them,instay themselves there andchanges thusinold residents are (c) The indirectly distribution of daily changes the Paris temperatures in sometimes (d) The distribution of daily the Paris temperatures in being “squeezed”. the 1970s.indirectly “squeezed”. the 1980s. being A description of this phenomenon is included in the work of Sociologist Ruth Fig.this 11. The distribution of daily changes in the DJIAin and Pariswork temperatures. A description of phenomenon is situations included the of Sociologist Ruth GLASS at the same period, while similar were recorded in other major GLASS at the same period, while similar situations were recorded in other major cities Western bymake other Researchers. in realityinwe do have acountries, choice: we can decisions relationships are not constant, while in the great cities Western countries, bypreoccupied other Researchers. majority cases: (a) errors not its wellmore behaved, (b) Since then, the issue severalof scholars andarefor based oninthe potential sizes andhas consequences of Since then, issue has several scholars and(c) for its more of their valiancebelow, is not constant, thevarious distribution forecasting errors, and the we can also structure our livessummarized comprehensive approach arepreoccupied being from the errors are not stable, and,from worst the of all,various (d) the errors to be robust to such errors. In a way, which is the comprehensive approach are being summarized below, interpretations of the phenomenon of gentrification, the following: are not independent of each other. motivation of this issue, we make deep changes interpretations thecan phenomenon thecategory following: In a sense, theof phenomenon is dueof togentrification, a trend of a new of social groups in the decision process affected by future predictions. toThis “return” to the city,the leaving purlieus paper has outlined major the theme of this for several reasons: high costs in money References and time to travel theability purlieus to downtown, where work place is, lack of the special section of the from IJF. Our to predict 1. The term comes from Sociologist Ruth GLASS, 1912-1940. Ruth search GLASS for wasbetter born in sense of issafety at with the distributed residencies outside town centres, the future limited, the obvious consequence Berlin, whereofshe made herItfirst studies. In 1932 Goldstein, she published an important study entitled: D., & Gigerenzer, G. (2009). Fast and frugal forecasting. of high levels uncertainty. has proved such services of health, education, entertainment “atInternational the heart of the city”,25(4), (possibly) Journal of Forecasting, movements 760–772. for Youthpredictability Unemployment. The same evidence year sheand left Germany and after continuous limited using empirical lower living cost of, in “withdrawal” from private car easier access to markets, studies and research Geneva, Prague, London and NewW. York she back Grove, M., Zald, D.came H., Lebow, B. to S., London, Snitz, B.etc. E., where & Nelson, C. four concrete data sets. Moreover, it has documented (2000).In Clinical versus prediction: A meta-analysis. in According 1943 she published studies regarding cityphenomenon planning. 1950 shemechanical became teacher in the to another approach, the is due to a systematic and our inability to assess uncertainty correctly and Psychological Assessment, Her 12(1),public 19–30. action and University informal College of London, where she continued her social research. long-term effort by organized groups, manufacturers, brokers of buying reliably in real-life situations, and discussed Hogarth, R., ENGLISH & Gaba, A. (2009). Dance with chance: her work are characterized by has a passion forthe justice.Makridakis, See also:S.,COLLINS DICTIONARY. and selling real estate, etc., for the depreciation initially of the urban web, in MakingWIKIPEDIA: luck of workpart for you. Oxford: Oneworld. major problems involved. Unfortunately, patterns and 10th edit. Wil. COLLINS SONS AND Co Ltd. London 2009. The Free Encyclopedia: G. ALEXANDRI: http://www.uncanny.net/ wetzel/gentry.htm a Gentrification: variety of ways, in order Abstract. to achieve the “assisted”, “voluntary”, (actually 252125 11