THE EXPECTED GROWTH OF POPULATION

At the outset, it must be emphasized that nobody can predict population growth with a high degree of accuracy. Population experts have had many opportunities in the past to demonstrate their inability to foresee the future clearly, and they will undoubtedly have many more opportunities to do so in the future. The trouble is, of course, that people do not always behave as we expect them to. Some of the strengths and weaknesses of earlier attempts to forecast population growth can be illustrated by projections prepared by Pascal K. Whelpton in 1927 (Whelpton, 1928). These were the first projections for the United States made by the so-called component method. With this method each of the three com-ponents of growth—fertility, mortality, and migration—is projected separately. Projections are prepared for each age-sex group, and the results are added to obtain a figure for the total population. Whelpton's 1927 forecasts were only 0.5 percent above the correct 1930 population, but by 1940 they were 4.6 percent too high. They nearly hit the mark in 1950, 23 years after they were prepared