Development and validation of a needs-based quality of life instrument for osteoarthritis

Objective. To develop and validate a disease-specific quality of life (QOL) measure for osteoarthritis (OA), the OAQoL, using the needs-based conceptual model. Methods. In the first phase of this study, in-depth, semistructured interviews were conducted with 44 OA patients to explore the issues associated with impact of OA and to derive items for a draft OAQoL questionnaire. In phase 2, 17 OA patients were interviewed on the relevance, clarity, and ease of completion of the measure in structured interviews. In phase 3, the draft questionnaire was mailed to 635 patients to test the psychometric properties of the questionnaire using Rasch analysis. Test-retest assessment of the revised questionnaire was performed in phase 4 by mailing the questionnaire to an additional 201 participants, with a second questionnaire repeated 2 weeks later. Results. A 38-item draft measure was devised during phase 1 and mailed in phase 2. Rasch analysis of the draft questionnaire (n = 259) indicated initial misfit, which was rectified with the removal of 13 problematic items (chi(2)[75] = 83.602, P = 0.232). For the test-retest assessment (n = 60), 3 additional items were removed, leaving a 22-item OAQoL that demonstrated good fit to the Rasch model (chi(2)[44] = 44.559, P = 0.533) with excellent test-retest correlation (p = 0.925, P < 0.001; z = -0.06, P = 0.995). Conclusion. The OAQoL is a simple and easy to use 22-item unidimensionalquestionnaire developed specifically to assess the impact of OA on QOL. The measure has been developed as a true patient-based questionnaire and demonstrates good psychometric properties, including test-retest reliability.