chapter  15
Developmental Design and Change in Subject Populations with Age
Pages 7

Figure 15-1 shows, in abbreviated and simplified form, some data on age structures and mortality probabilities in the United States. The left-hand part of the figure shows (in approximation) the estimated distribution of the population in the United States in 1830, 1870, and 1969, as published by the United States Bureau of Census. It illustrates the changing nature of age structures at different points in historical time, the most recent age structure exhibiting the highest proportion of elderly persons. For example, the lefthand part of Figure 15-1 indicates that, whereas in 1830 about 33% of the living population was 10 years old or younger, in 1969 this age group constituted only 18% of the total population.