2. POPULATION GROWTH WHAT IS DEMOGRAPHY? - Demography is the scientific study of human population. - It examines population trends in the past as well as its present-day characteristics. - Demographers measure population growth by using a number of rates (tasas): birth rate, fertility rate and mortality rate.
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THE BIRTH RATE AND FERTILITY RATE The birth rate measures the number of births in an area over a year. It shows annual births per 1,000 people. It is related to the fertility rate. Fertility rate is the average number of babies born to women over the entire period when they can have children, between the ages of 15 and 45. Many different factors affect the fertility rate: - cultural and economic factors such as : - wether women work, - the age when they begin to have children - the availability of contraceptives.
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Before the 19 th century: - Birth rate and fertility rate were very high in everywhere.
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In the 19 th and 20 th centuries: - The number of birds began to fall raidly in developed countries. - The birth rate and fertility rate stayed at very high levels in poorer countries and remain that way today.
2. POPULATION GROWTH THE MORTALITY RATE
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The mortality rate measures the number of deaths in an area over a year. It shows annual deaths per 1,000 people. Before the 19 th century, it was high because people had poor health and nutrition. This made them vulnerable to epidemics. In the 19 th and 20 th centuries, living conditions improved in developed countries and the situation changed. In recent decades, the mortality rate has fallen in many developing countries thanks to health programmes and improved sanitation. Infant mortality rate is still very high in regions like Africa. In recent years: - The proportion of older people in developed countries has increased considerably. - Older people are much more likel than younger people to die each year. - For that reason, the difference between the mortality rate in richer and poorer countries has declined.
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NATURAL INCREASE AND LIFE EXPECTANCY Natural increase is the difference between the number of births and deaths in a population. It s positive when the birh rate is higher than the death rate, but it is negative when there are more deaths than births. Today, it is low or negative in many developed countries. Their poplation only grows slowly unless thy receive a good deal of immigration. And i is very high or positive in most parts of Asia, Africa and Latin America. We usually measure the rate of natural increase. This figure is calculated by subtracting the mortality rate from the birth rate. Another key indcator is life expectancy at birth: this is the average life span (period of time) of people in a particular society. Life expectancy varies very much from one country to another. In developed countries it is about 77 years and it is only 45 n the poorest countries.