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In Brief: Disability: Federal Survey Definitions, Measurements, and Estimates

This In Brief summarizes the AARP Public Policy Institute data digest, Disability: Federal Survey Definitions, Measurements, and Estimates. Disability definitions are important for federal and state policies, programs, and planning, as well as for individuals with disabilities and their families. How federal and state programs define disability determines who will qualify for and how they will receive benefits from Social Security, Medicare, Medicaid, and state and local programs.

Reliable estimates of the number of people with disabilities are critical for federal and state agencies because the definition of disability ultimately determines the costs of the various programs.

The data digest examines how four national surveys, sponsored by the federal government, define and measure a critical aspect of disability, namely whether the disability limits a person's ability to perform everyday life activities, including activities of daily living (ADLs) and instrumental activities of daily living (IADLs). The four surveys explored are the American Community Survey (ACS), the Survey of Income and Program Participation (SIPP), the National Health Interview Survey (NHIS), and the National Long-Term Care Survey (NLTCS).

Summary of Findings

See chart below.


Much of the variation in disability prevalence rates occurs because each of the surveys differs in its measurement of the level of need or severity of daily limitations. Specifically, the NLTCS asks respondents if they "received help" to perform the activity, the SIPP and NHIS ask if respondents "needed help," while the ACS asks about "difficulty" in performing certain activities. The surveys also differ in their consideration of the length of time an individual has had, or is expected to have, a disability or conditions causing a disability.

Coordinated efforts among government agencies could reconcile major discrepancies and facilitate greater consistency in disability definitions and measures used across major national surveys.

(Click here to see Summary of Activity Limitation Measures and Disability Prevalence in Four National Surveys.)


  1. AARP Public Policy Institute Data Digest 98 (July 2004)

Written by Steven R. Gregory, AARP Public Policy Institute
July 2004
©2004 AARP
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