Objective: We aimed to develop a questionnaire assessing fears and beliefs of patients with knee OA.
Design: We sent a detailed document reporting on a qualitative analysis of interviews of patients with knee OA to experts, and a Delphi procedure was adopted for item generation. Then, 80 physicians recruited 566 patients with knee OA to test the provisional questionnaire. Items were reduced according to their metric properties and exploratory factor analysis. Reliability was tested by the Cronbach α coefficient. Construct validity was tested by divergent validity and confirmatory factor analysis. Test-retest reliability was assessed by the intra-class correlation coefficient (ICC) and the Bland and Altman technique.
Results: 137 items were extracted from analysis of the interview data. Three Delphi rounds were needed to obtain consensus on a 25-item provisional questionnaire. The item-reduction process resulted in an 11-item questionnaire. Selected items represented fears and beliefs about daily living activities (3 items), fears and beliefs about physicians (4 items), fears and beliefs about the disease (2 items), and fears and beliefs about sports and leisure activities (2 items). The Cronbach α coefficient of global score was 0.85. We observed expected divergent validity. Confirmation factor analyses confirmed higher intra-factor than inter-factor correlations. Test-retest reliability was good, with an ICC of 0.81, and Bland and Altman analysis did not reveal a systematic trend.
Conclusions: We propose an 11-item questionnaire assessing patients' fears and beliefs concerning knee OA with good content and construct validity.