A comparative analysis of ADL questions in surveys of older people.

This article describes questions designed to assess limitations with respect to activities of daily living (ADLs) that were asked on the first wave of the AHEAD study, and it assesses their cross-sectional measurement properties. It also provides comparisons between those questions and parallel questions that have been asked on two other surveys of the elderly population in the United States: the 1984 Supplement on Aging (SOA) to the National Health Interview Survey and the screener for the 1982 National Long Term Care Survey (NLTCS). It also compares a single item from the 1990 Census. It then compares the ways in which the same individuals answer these different versions of ADL questions, using data from subsamples of the AHEAD respondents who were also asked the SOA, NLTCS, or Census questions. The analysis shows that there is a substantial amount of measurement error in the answers to ADL questions, and it suggests that this is a major contributor to apparent improvements and declines in functional health observed in longitudinal data.