developed several decades ago in response to the recognized need to assess functional status and disability rather than relying solely on measures of self-perceived health or data on previous health histories. ADLs measure people’s abilities to perform basic tasks of daily life without assistance, including eating, dressing, bathing, using the toilet, and getting in and out of bed. IADLs measure people’s abilities to function independently in carrying out such activities as housework, preparing meals, shopping, managing money, and using the telephone. Questions about ADLs and IADLs are easy to administer to obtain self-reports or reports from caregivers. Estimates of the number and characteristics of older adults with difficulties in performing ADLs have important implications for health policies and programs and associated costs of health care for the elderly population.

Data on ADLs from the National Long-Term Care Survey (NLTCS) showed a marked decline in prevalence rates of disability among the elderly population from 25 to 19 percent over the period 1984 to 1999, an annual decline of nearly 2 percent per year from 1984 to 1999 (Manton et al., 1997; Manton and Gu, 2001). Researchers have identified some of the factors contributing to the decline: improvements in medical treatment including new and improved medicines and technology, improvements in health behavior, increased use of assistive devices to help people cope with impairments, environmental changes, changes in socioeconomic status and exposure to disease, and increase in educational attainment and related changes in occupational composition among older people.

Other research has broadly supported those findings, although with variations in the estimates of prevalence of ADLs or IADLs. However, not all studies have found declines for all measures (see, e.g., Crimmins et al., 1997; Waidman and Liu, 2000; Schoeni et al., 2001; Freedman et al., 2002; Freedman, 2006). Although the focus of this workshop is disability measurement in late life, note that trends in reported disability rates among younger cohorts, especially those 30–50 years of age, appear to be rising even as the elderly are becoming less disabled (see, e.g., Lakdawalla et al., 2004; Soldo et al., 2006).

Because of these inconsistencies, several efforts have been undertaken to examine the estimated prevalence rates and trends in disability. In 1988 the Federal Interagency Forum on Aging Related Statistics appointed a committee to systematically examine the different estimates from the various surveys measuring ADLs. The committee found substantial differences in the prevalence of disabilities for the elderly population across the various national surveys. Sources of variation included diversity in conceptual definitions of disability, the nature of reference periods used for recall, the disability measures used, the wording of questions, the sampling frame, the reporting rules for answering ADL questions, the order of the questions on the questionnaire, the modes of data collection (in person, by telephone,

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