Background: There is little epidemiologic data on the development of disability over time in older persons. This study uses prospective data from cohorts followed annually for 6 to 7 years to identify persons who developed severe disability and to characterize the time course of their disabling process and subsequent mortality.
Methods: Incidence rates of severe disability, defined as need for help in three or more activities of daily living (ADLs), were estimated for 6,640 persons who had not reported severe disability at baseline and at the first four annual follow-up visits. Among persons developing severe disability, those who reported no need for help in ADLs in previous interviews were defined as cases of catastrophic disability, and those who had previously reported some disability in ADLs were defined as cases of progressive disability.
Results: Overall, 212 subjects developed progressive and 227 developed catastrophic disability. The rates of progressive disability and catastrophic disability were 11.3 and 12.1 cases per 1,000 person-years, respectively. For both types of disability, incidence rates increased exponentially with age, but the increase was steeper for progressive disability. At ages 70-74, less than 25% of severe disability was progressive, while over age 85 progressive disability represented more than half of severe disability. Incidence rates of total and both types of severe disability were similar in men and women. Mortality after severe disability onset was extremely high. Survival was unrelated to age at disability onset and type of disability but was significantly longer in women than in men (median 3.44 vs 2.12 years; p < .0001).
Conclusion: Tracking the development of disability provides new and important insights into the disability experience in older men and women that are potentially relevant in planning preventive, intervention, and long-term care strategies.