Abstract
BACKGROUND: The psychometric properties of Patient Reported Outcomes Measurement Information System (PROMIS) instruments have been explored in a number of general and clinical samples. No study, however, has evaluated the psychometric function of these measures in individuals with symptomatic knee osteoarthritis (KOA). The aim of this project was to evaluate the construct (structural) validity and floor/ceiling effects of four PROMIS measures in this population. METHODS: We conducted a secondary analysis of baseline data from a randomized trial comparing Tai Chi and physical therapy. Participants completed four PROMIS static short-form instruments (i.e., Anxiety, Depression, Physical Function, and Pain Interference) as well as six well-validated (legacy) measures that assess pain, function, and psychological health. We calculated descriptive statistics and percentages of participants scoring the minimum (floor) and maximum (ceiling) possible scores for PROMIS and legacy measures. We also estimated the association between PROMIS scores and scores on legacy measures using Spearman's rank correlations coefficients. RESULTS: Data from 204 participants were analyzed. Mean age of the sample was 60 years; 70% were female. The PROMIS Anxiety and Depression had floor effects with 17 and 24% of participants scoring the minimum, respectively. PROMIS Anxiety and Depression scores had strongest associations with general mental health, including stress (Perceived Stress Scale, r ≥ 0.65) and depression (Beck Depression Index-II, r = 0.70). PROMIS Pain Interference scores correlated most strongly with measures of whole body pain (Short-Form 36 Bodily Pain, r = -0.73) and physical health (Short-Form 36 Physical-Component Summary, r = -0.73); their correlations were lower with other legacy measures, including with the WOMAC knee-specific pain (r = 0.47). PROMIS Physical Function scores had stronger associations with scores on the Short-Form 36 Physical Function (r = 0.79) than with scores on other legacy measures. CONCLUSION: The four PROMIS static-short forms performed well among individuals with symptomatic knee osteoarthritis as evidenced in correlations with legacy measures. PROMIS Anxiety and Depression target general mental health (e.g., stress, depression), and PROMIS Pain Interference and Physical Function static-short forms target whole-body outcomes among participants with symptomatic knee osteoarthritis. Floor effects in the PROMIS Anxiety and Depression scores should be considered if needing to distinguish among patients with very low levels of these outcomes. TRIAL REGISTRATION: Clinicaltrials.gov NCT01258985. Registered 10 December 2010.