Development of an Expanded Measure of Physical Functioning for Older Persons in Epidemiologic Research

We scaled a measure of physical functioning to a population-based normative sample by extending self-reported basic and instrumental activities of daily living with items from the Medical Outcomes Study 12-Item Short Form Survey. We used item response theory to place items administered to a sample of older elective surgery patients on a common metric linked to the Patient Reported Outcomes Measurement Information System (PROMIS) normative sample using published data. The summary measure for physical functioning was internally consistent (Cronbach's α = .83), reliable across a broad range of functioning, and was moderately correlated with walking speed (r = .52) and energy expenditure (r = .40). Demonstrating predictive criterion validity, less impaired scores were associated with lower risk of discharge to a rehabilitation facility (odds ratio = .38, 95% confidence interval [CI] [0.22, 0.66]) and shorter hospital stays (incidence rate ratio [IRR] = 0.87, 95% CI [0.79, 0.97]). Our approach may facilitate direct comparison of physical functioning measures across existing and future studies using a common, population-based metric, when overlapping items with the National Institutes of Health (NIH) PROMIS item bank are present.