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Executive Summary
Pages 1-14

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From page 1...
... The Panel on Population Projections was asked to examine these projections: to assess their assumptions, estimate their accuracy and uncertainty, evaluate the implications of current demographic research for projection procedures, and recommend changes where appropriate as well as research that might improve projections. Generally, the panel finds current world projections up to 2050 to be plausible, although they could indeed be improved in some ways, and their uncertainty deserves more precise quantification.
From page 2...
... In the next half-century, the proportion of the population aged 65 and older is expected to rise from 5 to 15 percent in the developing regions, and from 14 to 26 percent in the industrial regions. Future population growth and changes in the age composition of the population are determined by levels and trends in the following factors: · Fertility.
From page 3...
... Movement of people between countries has no direct effect on world population growth, but it affects growth in particular countries and regions. Net migration levels are projected to continue to vary across countries, slightly retarding shifts in the regional balance of populations.
From page 4...
... Past forecasts, for instance, produced slightly too high world projections for 2000, due mainly to larger than expected fertility declines in a few major countries. Such unexpected fertility declines will never be exactly replicated, and future demographic conditions generally are likely to diverge from conditions that prevailed during the periods covered by past forecasts.
From page 5...
... Couples want smaller families for several reasons: children have become less household assets than household liabilities and require increasingly costly parental investments; the idea of and the means for birth control have been increasingly acceptable after diffusion through media, health services, and interpersonal channels; and the odds of child survival have substantially improved, so that fewer births are needed to achieve a desired family size. The relative importance of each factor in couple decisions has been much debated, but that each at least plays some role is broadly accepted.
From page 6...
... This question is immediately relevant for demographically advanced developing countries as well as for all industrial countries, which are already at these levels. This group of countries includes fully 50 percent of current world population.
From page 7...
... Before the transition started, life expectancy rarely exceeded 40 years, and year-to-year mortality would fluctuate sharply. With progress in standards of living, nutrition, medicine, and public health, annual fluctuations in mortality were gradually reduced, and life expectancy began a long, steady rise.
From page 8...
... In recent decades, another crisis with somewhat similar broad impact was the collapse of the Communist bloc, which accelerated the fall in life expectancies in Eastern Europe. Crises of this type and scale do affect long-term trends in life expectancy, unlike most natural disasters, which merely produce fluctuations in trend.
From page 9...
... In the 1990s, unexpected flows of migrants have occurred after humanitarian catastrophes such as the mass killings in Rwanda, civil war in Liberia, and the invasion of Kuwait. Mass migrations of this sort have been the primary cause of "demographic quakes" sudden and extreme changes in population growth rates and have been a major source of error in past population projections in the affected countries.
From page 10...
... The historical record on which these prediction intervals are based includes some major unanticipated influences on demographic behavior, such as the HIV/AIDS epidemic, civil wars, and other disturbances that produced crisis migration and mortality in several countries. To some extent, therefore, these predictive intervals allow for unexpected events.
From page 11...
... The panel's review finds that the projection assumptions regarding future trends in fertility, mortality, and migration are generally supported by available scientific evidence. Conclusions The panel therefore concludes that these current world population projections to 2050 are based on reasonable assumptions and provide plausible forecasts of world demographic trends for the next few decades.
From page 12...
... Better estimates of demographic parameters have been critical in improving forecasts in the past, especially for developing countries. More accurate data not only improve the base estimates from which projections start but also enhance understanding of the demographic dynamics of specific countries.
From page 13...
... The panel has attempted to estimate prediction intervals for projected population based on an analysis of errors in past projections. The analysis involved assessments of the accuracy of more than 1,000 country projections made in recent decades but was still limited because the latest projections cannot yet be assessed.


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