A more detailed picture of trends in prevalence emerges when the age-specific rates in Figures 2-5 and 2-6 are examined. Prevalence rates are relatively flat for most age groups over the entire period, but there is some increase in the prevalence of activity limitation in the early 1970s, especially for those age 45-64. The changes of definition clearly show up between 1981 and 1983 in Figure 2-6 as an increase in the proportion of children with limitation in major activity and a decrease in the proportion of people 65 and over with limitation in major activity. The differences are especially evident in the figures for people 65 and over with limitations in major activity, as one would expect. The steady overall prevalence of any limitation reflects the balancing of a substantial decrease in prevalence among people over 65 against a smaller proportional increase (in a larger population) among people under age 18.
Colvez and Blanchet (1981) note the increased prevalence of activity limitation in the NHIS data (between 1966 and 1976) and discuss a number of possible explanations. Because the increase is concentrated in men age 45-64 who report that they are unable to work, Wilson and Drury (1984) suggest that the increasing availability of health-related retirement benefits during that period, and perhaps decreasing stigma attached to "disability," could explain a large part of the increase in activity limitation during that period. They also suggest that increased access to health care (especially screening for hypertension and other asymptomatic chronic diseases) could result in physician-ordered activity reduction and improved awareness of