Psychometric Comparison of the PROMIS Physical Function CAT With the FAAM and FFI for Measuring Patient-Reported Outcomes

Background: Selecting optimal patient-reported outcome (PRO) instruments is critical to improving the quality of health care. The purpose of this study was to compare the reliability, responsiveness, and efficiency of three PRO measures: the Foot and Ankle Ability Measure–Activity of Daily Living subscale (FAAM_ADL), the Foot Function Index 5-point verbal rating scale (FFI-5pt), and the PROMIS Physical Function computerized adaptive test (PF CAT). Methods: Data were aggregated from 10 clinical sites in the AOFAS’s National Orthopaedic Foot and Ankle Research (OFAR) Network from 311 patients who underwent elective surgery for a disorder of the foot or ankle. Patients were administered the FAAM_ADL, FFI-5pt, and PF CAT at their preoperative visit and at 6 months after surgery. Reliabilities were evaluated using a Rasch model. Responsiveness was calculated using paired samples t test and efficiency was recorded as number of seconds to complete the instrument. Results: Similar reliabilities were found for the three instruments. Item reliabilities for FAAM_ADL, FFI-5pt, and PF CAT were all .99. Pearson reliabilities for FAAM_ADL, FFI-5pt, and PF CAT were .95, .93, and .96, respectively. On average, patients completed the FAAM_ADL in 179 seconds, the FFI-5pt in 194 seconds, and the PF CAT in 44 seconds, (P < .001). The PF CAT and FAAM_ADL showed significant improvement (P = .01 and P = .001, respectively) in patients’ physical function after treatment; the FFI-5pt did not show improvement. Conclusions: Overall, the PF CAT performed best in terms of reliability, responsiveness, and efficiency in this broad sample of foot and ankle patients. It can be a potential replacement for the conventional PRO measures, but further validation is needed in conjunction with the PROMIS Pain instruments. Level of Evidence: Level I, prospective comparative outcome study.