or engagement may facilitate a more refined understanding of the shifts in population-level disability trends. Sorting out the roles of factors earlier in life may require panel surveys that start earlier in life. Inclusion of a standardized core set of disability measures that apply across all ages, as well as life course-specific measures, also may prove useful.

Looking forward, there is debate about the implications of these trends for public and private expenditures^18,47-49. Some researchers are optimistic that the declines in rates of late-life disability will ultimately lead to (all else being equal) lower medical costs; others are dubious about whether declines will ultimately lead to savings. Whether declines in late-life disability will continue into the future is unclear, given, for example, the impending increases in rates of obesity⁵⁰ and related chronic conditions and the slowing increases in educational attainment³⁰.

Indeed, the impending growth of the older population suggests that it will be important to continue to achieve declines in rates of late-life disability. Projections of the size of the older population with disabilities, which depend upon assumptions about mortality and disability rates into the future, suggest that declines in disability rates will need to continue at the rates observed during the 1990s (on average, 1 to 2 percent per year) for this group to remain stable⁵¹. Projections that assume much lower rates of decline portend large increases in the number of older people with a disability, from 6 million today to 10 million in 2050⁵². How these population shifts will influence the composition of the population of people with disabilities is unclear and merits further study.

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