Reproducibility of performance-based and self-reported measures of functional status.

BACKGROUND: The reproducibility of a performance-based and a self-reported measure of functional status was investigated, as well as the impact of age and cognitive function on the reproducibility.
METHODS: Of a random sample of 114 men of the 1995 survey of the Zutphen Elderly Study, 105 men (aged 79.9 +/- 4.5 years) participated in a test-retest study. They filled out a questionnaire on disabilities and carried out performance tests twice, in a 2-week interval. Four performance tests were administered (standing balance, walking speed, chair stand, and external shoulder rotation), and a summary performance score was constructed. The number of self-reported disabilities in basic activities of daily living, mobility, and instrumental activities of daily living were assessed. Kappa statistics and Pearson correlation coefficients between test and retest measurements were computed for the total group and stratified by age and cognitive function.
RESULTS: Three performance tests and the summary performance score had fair to good reproducibility (walking speed: Pearsons r = .90, chair stand: r = .82, shoulder rotation: kappa = .49, summary score: kappa = .52). Only the test for standing balance was poorly reproducible (kappa = .29). The self-reported functional status was fairly to good reproducible (kappa = .63, r = .87). Self-reported functional status was significantly less reproducible in very old and cognitively impaired than in younger and nonimpaired individuals.
CONCLUSIONS: In the elderly male subjects, performance tests and self-reported disabilities had moderate to good reproducibility, with the exception of the test for standing balance. In very old or cognitively impaired populations, self-reported functional status may have a lower reproducibility.