RESUMEN
PURPOSE: Self-reported and performance-based instruments are both necessary for a comprehensive view of the functioning of institutionalized older adults. Our aim was to assess the reliability and measurement error of the 12-item World Health Organization Disability assessment Schedule and compare these indexes against performance-based tests. MATERIALS AND METHODS: One hundred participants from Nursing Homes and Day Care Centers were assessed twice (two days to one week apart) by two independent assessors. Reliability and measurement error indexes were calculated. RESULTS: Reliability of the World Health Organization Disability assessment Schedule total score, and of three performance tests was appropriate for individual comparisons (ICC ≥ 0.92). Reliability for the five times seat to stand test was appropriate for group comparisons only (ICC = 0.84). The high measurement error of the timed up and go test (SEM = 4.25; MDC = 11.78) and of the five times seat to stand test (SEM = 3.47; MDC = 9.62) and the number of participants unable to perform them (TUG: n = 11; FTSST: n = 41) suggest that these tests are less suitable to monitor individual changes. CONCLUSIONS: The 12-item World Health Organization Disability Assessment Schedule total score, the gait speed and hand grip tests could be used to monitor changes at both the individual and group level in a population with decreased functioning. Implications for Rehabilitation The 12-item World Health Organization Disability assessment Schedule, could be used to monitor changes in perceived functioning both at the individual and group level in institutionalized ambulatory older adults. The gait speed and hand grip tests could be used to monitor changes in performance both at the individual and group level in institutionalized ambulatory older adults' functioning. The utility of the time up and go and of the five times seat to stand test might be of limited value when aiming to monitor changes in institutionalized older adults' functioning.