A Patient-Reported Outcomes Measurement Information System Short Form for Measuring Physical Function During Geriatric Rehabilitation: Test-Retest Reliability,Construct Validity,Responsiveness, and Interpretability

ObjectivesTo study the test-retest reliability and measurement error, construct validity, responsiveness, interpretability, and floor/ceiling effects of a Patient-Reported Outcomes Measurement Information System (PROMIS) short form designed to measure physical function in geriatric rehabilitation patients (PROMIS-PF-GR).DesignProspective cohort.Setting and ParticipantsInpatient geriatric rehabilitation patients.MethodsWe evaluated the test-retest reliability by re-administering PROMIS-PF-GR 3 to 5 days after the admission measurement. The intraclass correlation coefficient (ICC) was calculated to determine test-retest reliability; an ICC of ≥0.70 was considered sufficient. Measurement error was established by calculating the standard error of measurement and smallest detectable change. Construct validity and responsiveness were determined by testing a priori formulated hypotheses (criterion: ≥75% hypothesis not rejected). Interpretability was evaluated by calculating the minimal important change using predictive modeling and a global rating as criterion for change. Floor/ceiling effects were established by calculating the percentage patients with the minimum/maximum raw score (criterion: ≤15%) at admission and discharge.ResultsA total of 207 patients participated in the study [mean ± standard deviation age (80 ± 8.3 years), 58% female]. More than one-half of patients (56%) reported to be improved during rehabilitation. The ICC was 0.79 (95% confidence interval 0.70–0.84), the standardized error of measurement was 3.8, and the smallest detectable change 10.6. None of the 4 hypotheses for construct validity were rejected; 2 out of 5 hypotheses for responsiveness were rejected. The minimal important change was 8.0 (95% confidence interval 4.1–12.5). No floor/ceiling effects were found.Conclusions and ImplicationsThe PROMIS-PG-GR showed sufficient test-retest reliability, measurement error, and construct validity. We did not find sufficient evidence for responsiveness, which may be due to the unexplained weak correlation between the PROMIS change score and the Global Rating Scale. We still recommend the use the PROMIS-PG-GR for measuring self-reported physical function in geriatric rehabilitation.