The purpose of this study was to evaluate the measurement properties of the Osteoporosis Assessment Questionnaire-Physical Functioning (OPAQ-PF). Based on this study, the OPAQ-PF has confirmed unidimensionality and acceptable reliability, construct validity, and sensitivity to change in a recent fracture/no recent fracture osteoporosis sample.
Methods: Dimensionality was established through exploratory and confirmatory factor analysis. Patients completed three patient reported outcome (PRO) measures and four performance-based measures (PBMs) at baseline to enable an evaluation of construct validity. Patients without a recent fracture completed the OPAQ-PF 2 weeks after baseline to enable an evaluation of test-retest reliability. Ability to detect change and interpretation of change were investigated following completion of the OPAQ-PF 12 and 24 weeks postbaseline by patients with a recent fracture.
Results: A prospective psychometric validation study in 144 postmenopausal women, with moderate to severe osteoporosis, 37 of whom had experienced a recent fragility fracture (<6 weeks). Unidimensionality was established for the OPAQ-PF by factor analysis. The OPAQ-PF had good internal consistency (α = 0.974) and test-retest reliability (mean intraclass correlation coefficient (ICC) 0.993. The OPAQ-PF differentiated between patients with/without recent fracture, and by severity of osteoarthritis; it correlated strongly with hypothesized-related scales and PBMs (r > 0.3, p < 0.001). Ability to detect change was established with high correlations between changes in OPAQ-PF score and changes in global concept scores in recent fracture patients (r ≥ 0.6, 24-week change). Effect size of change on OPAQ-PF score increased by level of global change (p < 0.001). Anchor-based methods identified an OPAQ-PF change of 10 at an individual patient level and 20 at a group level as meaningful to patients.
Conclusions: The OPAQ-PF has confirmed unidimensionality and acceptable reliability, construct validity, and sensitivity to change in a recent fracture/no recent fracture osteoporosis sample.