Measuring physical function in community-dwelling older persons: a comparison of self-administered, interviewer-administered, and performance-based measures.

PURPOSE: To compare two self-administered, one interviewer-administered, and one performance-based measure of physical function in community-based older persons.
METHODS: Eighty-three subjects were recruited from meal sites, senior recreation centers, and senior housing units for a comprehensive geriatric assessment program. At the time of screening, study participants self-administered the Functional Status Questionnaire (FSQ) and were administered the Katz Activities of Daily Living (ADL) and the Older Americans Resources and Services Instrumental Activities of Daily Living (OARS-IADL) instruments by interview. Participants also completed the Physical Performance Test (PPT) and were given the Medical Outcomes Study SF-36 to self-administer on site or at home and return by mail.
RESULTS: All 83 subjects completed FSQ, Katz ADL, OARS-IADL, and PPT; 72 returned SF-36 forms. Correlations between the two self-administered physical function measures (FSQ and SF-36) were higher than between self-administered and interviewer-assessed (ADL and OARS-IADL) or performance-based (PPT) measures. When assessed for construct validity, the self-administered, OARS, and PPT measures had comparable correlations with role limitations as a result of physical health problems, but relationships between physical functional status measures and other SF-36 measures of health were inconsistent.
CONCLUSION: The relationships between commonly used self-administered, interviewer-administered, and performance-based measures of physical function were inconsistent and weak, suggesting that these instruments are not measuring the same construct.