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Basics of SPSS: Part 1
ASK Week – Autumn 2012
Purpose and use of SPSS Open SPSS What is a Variable? Defining variables in SPSS Entering Data Open and save data files Import data from Excel Handling missing data
PURPOSE & USE OF SPSS SPSS is a Statistical Software Package SPSS is a tool It only does what it’s ‘told’ to do. It does not think for you It is not a black box You need to know the correct statistics for your research BEFORE using SPSS. If you understand the statistics, then you are ready to do analysis in SPSS.
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Select SPSS 18 from the list
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Type SPSS 18 into the search box
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Click on the Windows Start Icon
Open NEW data file
Always open SPSS first, then open or type in data.
DEFINE VARIABLES
Enter variable names in the first column. We will look at all the columns in more detail shortly.
ENTER DATA
Each variable name will appear as a column heading replacing var.
Enter the data for each variable from the Data View. We will also look at entering data in more detail shortly.
W H AT HOW
I S A VA R I A B L E ?
D O W E D E F I N E VA R I A B L E S I N S P S S ?
WHAT IS A VARIABLE? A measurement: A characteristic (e.g., Gender, Age, Height, Weight…) Time points (e.g., pre-test, post-test, T0, T1, T2…)
Experimental Condition (e.g., Condition, Experimental grp…)
Opinion/belief (e.g., A survey question which asks for a respondent’s level of agreement with a statement)
Etc…
Variables go in Columns
What is your gender?
Male or Female
Variables go in Columns
How long does it take, on average, to commute into Uni?
Variables go in Columns
What is your main mode of transport to Uni?
Variables go in Columns
Indicate your level of agreement with the following statement: “Most days, my commute causes me to feel stressed when I arrive at university�.
IDENTIFYING VARIABLES Questionnaire Responses Random sample of 200 residents of Uxbridge.
Asked respondents’ their view on stem cell research using a 3 pt. Likert Scale (Disagree, No Opinion, Agree). Asked respondents’ if they believed global warming was an important issue using a 5 pt. Likert Scale (Strongly Disagree to Strongly Agree).
IDENTIFYING VARIABLES Questionnaire Responses Resident
StemCell
GlobalWarming
1
Agree
Strongly Agree
2
Undecided
Agree
3
Undecided
Strongly Disagree
4
Disagree
Undecided
…
…
…
Variables go in Columns
Experimental Condition Cond 1 and 2 are independent, NOT repeated measures.
Score on a test
IDENTIFYING VARIABLES CAFFEINE AND SLEEP 30 participants were used to investigate the effect of caffeine on their ability to sleep. The 30 participants were randomly assigned to one of 2 conditions: No caffeine (control) or one dose of caffeine every 3 hours from 9am-6pm. The study measured participants ability to sleep by taking the average number of hours slept per night over a 2 week period.
IDENTIFYING VARIABLES Caffeine and Sleep Participant
Condition
AvgHoursSlept
1
Control
7.2
2
Caffeine
6.7
3
Caffeine
6.3
4
Control
6.9
…
…
…
Variables go in Columns
Status at entrance to care facility
Variables go in Columns
Anxiety level measured at 3 time points for each participant
Variables go in Columns
Why not enter like we did for
?
IDENTIFYING VARIABLES
Fitness regime 50 participants of varying fitness levels were used to investigate whether personal trainers make a significant difference in ones fitness. Participants were randomly assigned to one of two training groups: self training or professional trainer. Each participants 1 mile time (in mins) was recorded 2 days prior to the start of the study. Each group then followed a specific training regime for 30 days and their 1 mile time (in mins) recorded again.
Identify the variables for this problem
LEVELS OF MEASUREMENT Variables
Categorical
Scale
Qualitative
Quantitative
Nominal
Ordinal
(Unranked categories)
(Ranked categories)
Marital Status Political Party Eye Color
Satisfaction level Level of agreement
Not grouped
Height Weight Age No. of cars No. of students
• In SPSS, data is either Nominal, Ordinal or Scale. • It is essential to classify data correctly. - Incorrect classification… may result in incorrect analyses.
CODING
C AT E G O R I C A L VA R I A B L E S
OPEN SPSS E N T E R D ATA S AV E F I L E S
Coding Categorical Variables
Level of Measurement?
Categorical variables need to be coded Scale variables do not need to be coded
Coding Categorical Variables
0 0 1 0 1 1 0 1 0 1
Level of Measurement?
0 = Male 1 = Female
Coding Categorical Variables
Level of Measurement?
Scale, does not need to be coded
Coding Categorical Variables
1
Level of Measurement?
1 2 1 1 1 3 4 1 2
1 = tfl (i.e. public transport) 2 = Car 3 = Cycle 4 = Walk
Coding Categorical Variables
Indicate your level of agreement with the following statement: “Most days, my commute causes me to feel stressed when I arrive at university�.
Coding Categorical Variables
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Level of Measurement?
2 4 5 5 4 2 1 3 2
1 = Strongly Disagree 2 = Disagree 3 = I don’t know 4 = Agree 5 = Strongly Agree
Coding Categorical Variables
Data has been coded Now we’re ready to enter it in SPSS
Entering Data 1. Enter & define variables from Variable View.
• Variable names • Must begin with a letter • No spaces and no special characters (except _ )
Entering Data 1. Enter & define variables from Variable View.
• Type • Should (almost) always be numeric • SPSS cannot analyse non-numeric data
Entering Data 1. Enter & define variables from Variable View.
• Decimals • How many decimal places do you want to see in the Data View?
Entering Data 1. Enter & define variables from Variable View.
• Label • IMPORTANT!!! Make good labels! • Short description of the variable • This is what will be written on all graphs & tables
Entering Data 1. Enter & define variables from Variable View.
• Values (i.e., Value labels) • IMPORTANT!!! - Tell SPSS what all the codes represent! • This is what is written on all graphs & tables
Entering Data 1. Enter & define variables from Variable View.
Entering Data 1. Enter & define variables from Variable View.
• Missing • We will come back to this one shortly.
Entering Data 1. Enter & define variables from Variable View.
• Measure • Level of Measurement (Nominal, Ordinal, Scale) • By default ALL new variables are scale • YOU must choose the appropriate measure
Entering Data 2. Enter data from Data View.
• Variable names • Will become column headings in Data View.
Entering Data 2. Enter data from Data View.
• Rows • Subject entries • For example, participant responses to survey questions. Row 1 is participant 1, etc…
Entering Data
Now, let’s enter some data
SAVING YOUR SPSS FILES
SAVING YOUR SPSS FILES Locate a folder to save it in: On your H drive OR On your pen drive
Name it appropriately Extension .sav
OUTPUT FILE Shows output for ALL analysis run in SPSS Keeps a log of all activity of open data files Saved with the extension .spv
Everything done in SPSS is shown here, in outline form.
A data file was saved as SPSS_Part1_Ex7.sav. This was recorded in the log here.
CREATING A NEW SPSS FILE New data file New output file
OPEN AN EXISTING SPSS FILE Existing data file Existing output file ALWAYS open SPSS first! If you try opening a data file from a folder, SPSS will NOT work
…FROM EXCEL
THE EXCEL FILE… Log onto Blackboard. Go to the ASK section. “Workshop slides” “Statistics and SPSS Workshops” Download the Excel File: “CommutingSurvey.xlsx”
FOR EXAMPLE.
IMPORTING DATA FROM EXCEL.
Filename (.xlsx)
Variable names (Row 1)
Sheet1 contains the dataset
IMPORTING AN EXCEL FILE… Can be .xls OR .xlsx
Variable names CAN be imported too Must be in row 1 of the worksheet
Data will appear in SPSS Data View
IMPORTING DATA INTO SPSS 18
Existing data file
FOR EXAMPLE.
IMPORTING DATA FROM EXCEL.
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Select the Excel file
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Choose Excel file type to see your .xlsx
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Find the folder where you saved the file
FOR EXAMPLE.
IMPORTING DATA FROM EXCEL.
Is this range correct?
If NOT Enter correct range here
FOR EXAMPLE. Variable Names (from Row 1)
View all data
IMPORTING DATA FROM EXCEL.
FOR EXAMPLE.
IMPORTING DATA FROM EXCEL.
View and Define variables This variable name from Excel could not be used. SPSS made it a label and created a new variable name
H O W T O H A N D L E M I S S I N G D ATA
REPLACE MISSING VALUES
There are 3 missing values for TravelTimemin
• Replace missing values with a code • Use a code that will not occur for the variable • Let’s use -1, as negative time is not possible
REPLACE MISSING VALUES
Missing values have been replaced with -1 for TravelTimemin
CODE MISSING VALUES
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Remember‌ From Variable View Define the missing values
CODE MISSING VALUES
• Missing • Missing data must be coded too! • Chose a number not in the data, like 99 or 999 • Replace all missing values in your data with this code first
CODE MISSING VALUES
This is only a code – it tells SPSS what values represent missing values. It does not replace missing values with the code for you!
SPSS Survival Manual, 4th Edition (2010) by Julie Pallant. (For SPSS Version 15 or later)
Discovering Statistics Using SPSS, 3rd Edition (2009) by Andy Field. (For SPSS Version 15 or later)
ASK Week – Autumn 2012
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Find the slides (and much more) on Blackboard