Adaptation of the WOMAC for Use in a Patient Preference Study

OBJECTIVES: To adapt a patient-reported outcome (PRO) measure, the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), into efficacy attributes for a discrete choice experiment (DCE) survey designed to quantify the relative importance of endpoints commonly used in knee osteoarthritis (KOA) trials. METHODS: The adaptation comprised four steps: (1) selecting domains of interest; (2) determining presentation and framing of selected attributes; (3) determining attribute levels; and (4) developing choice tasks. This process involved input from multiple stakeholders, including regulators, health preference researchers, and patients. Pretesting was conducted to evaluate if patients comprehended the adapted survey attributes and could make trade-offs among them. RESULTS: The WOMAC pain and function domains were selected for adaption to two efficacy attributes. Two versions of the discrete choice experiment (DCE) instrument were created to compare efficacy using (1) total domain scores and (2) item scores for “walking on a flat surface.” Both attributes were presented as improvement from baseline scores by levels of 0%, 30%, 50%, and 100%. Twenty-six participants were interviewed in a pretest of the instrument (average age 60 years; 58% female; 62% had KOA for ≥ 5 years). The participants found both versions of attributes meaningful and relevant for treatment decision-making. They demonstrated willingness and ability to tradeoff improvements in pain and function separately, though many perceived them as inter-related. CONCLUSIONS: This study adds to the growing literature regarding adapting PRO measures for patient preference studies. Such adaptation is important for designing a preference study that can incorporate a clinical trial’s outcomes with PRO endpoints.