Detecting functional change in response to exercise in knee osteoarthritis: a comparison of two computerized adaptive tests

BACKGROUND: The intent of this study was to examine and compare the ability to detect change of two patient reported outcome (PRO) instruments that use a computerized adaptive test (CAT) approach to measurement. The Patient Reported Outcomes Measurement Information System (PROMIS®) Physical Function scale is a generic PRO, while the Osteoarthritis Computerized Adaptive Test (OA-CAT) is an osteoarthritis-specific PRO. METHODS: This descriptive, longitudinal study was conducted in a community setting, involving individuals from the greater Boston area. Inclusion criteria: age > 50, self-reported doctor-diagnosed knee osteoarthritis (OA) and knee pain. The PROMIS® Physical Function CAT and OA-CAT Functional Difficulty scale were administered at baseline and at the conclusion of a 6-week exercise program. Effect sizes (ES) were calculated for both measures, and bootstrap methods were used to construct confidence intervals and to test for significant ES differences between the measures. RESULTS: The OA-CAT Functional Difficulty scale achieved an ES of 0.62 (0.43, 0.87) compared to the PROMIS® Physical Function CAT ES of 0.42 (0.24, 0.63). ES estimates for the two CAT measures were not statistically different. CONCLUSIONS: The condition-specific OA-CAT and generic PROMIS® Physical Function CAT both demonstrated the ability to detect change in function. While the OA-CAT scale showed larger effect size, no statistically significant difference was found in the effect size estimates for the generic and condition-specific CATs. Both CATs have potential for use in arthritis research. TRIAL REGISTRATION: This trial is registered with ClinicalTrials.gov on 6/21/11 (Identifier NCT01394874)