Population Projections
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Main page Fertility, mortality and migration
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Information about the size of the future population is extremely valuable. With this information, governments can build the correct number of schools, hospitals and roads. A baby boom means an increase in demand for baby-food and infant products. The relative millitary strengths of neighbouring countries depend on the countries respective population.
Population projections are used to predict the future population. In the past, population projections use mathematical methods. This method expresses population as a function of time, with the exponential function being the most usual function used. Although reliable for short-term projections, mathematical methods give unrealistic values for long-term projections. A majority of population projections today use the cohort-component method. This method makes separate and independent projections of fertility, mortality and migration. The results of these three projections are then combined. Separate projections are carried out again. The process of separation and combination then continues over the projected time span. Carrying out a population projection is a straightforward process. Not only large agencies like the UN, Population Council or the Census Board can make population projections, anyone with the correct software can make a population projection. But whether or not a projected population will turn out to be true depends on the assumptions used. Will fertility increase, level off or decrease? Will there be more gains in life expectancy? Can migration be ignored?
Thus, a more important question is not what is the projected population, but what are the assumptions used when carrying out the projection. To obtain the correct assumptions, we need to study closely factors that affect fertility, mortality and migration. What if the assumptions used are wrong? Table 4 shows the consequences of making incorrect assumptions of fertility, mortality and fertility. However, these guidelines apply only for developed countries.
The table shows that fertility is the greatest determinant on future population. Thus, care must be taken when making a fertility assumption. This assumption must be based on factors like age of marriage, percentage of women entering the workforce, child-care facilities, government health programs and migration laws.
Table 5 shows the top ten countries with respect to population size in the year 2015. We note that seven of these countries are from Asia. Seven of the countries are categorised as today's developing countries. Certainly, by the year 2025, the population of developing countries will outnumber the developed countries by more than six times. Also, there is some debate which country will the most populous. Other projections predict that this country will be India and not China, due to China's one-child policy.
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carrying out a projection