(1) Background: to examine the psychometric properties of the Portuguese version of the Timed Instrumental Activities of Daily Living (TIADL) in nursing home residents. (2) Methods: Fifty-two participants (85.8 ± 4.2 years) were assessed on two occasions, 10-14 days apart. The same rater administered all assessments. Internal consistency was analysed through Cronbach's α. The reliability was estimated using the intraclass correlation coefficients (ICCs), and the standard error of the mean (SEM) was used to estimate the minimal detectable change (MDC). Construct validity was determined by Spearman's correlation coefficients. (3) Results: For internal consistency, Cronbach's α (0.81) revealed high internal reliability. All of the subtests demonstrated good or excellent reliability and also presented acceptable measurement precision, considering the criterion SEM < SD/2. According to Spearman's rho, correlations with the Portuguese version of the TIADL, the Useful Field of View test, and semantic and phonemic fluency tests were significant, with moderate positive and negative correlations (0.4 < rs < 0.69). (4) Conclusions: The Portuguese version of the TIADL had good to excellent test-retest reliability (ICC > 0.90) and acceptable measurement precision. This test could be a valuable clinical tool for assessing actual performance in instrumental activities of daily living in nursing home residents.
Keywords: instrumental activities; nursing homes; performance accuracy; reliability.