Assessing the content validity of a Patient Reported Outcome Measure item pool for Rheumatoid Arthritis Disease Activity using cognitive interviews

Objectives: Using Rasch measurement theory, an item pool of 12 questions has been identified, covering tenderness and swelling, disease activity, pain, physical functioning and stiffness for assessing the construct of RA disease activity. This study aimed to assess the content validity of this item pool using cognitive interviews. Methods: Participants were randomly sampled across varying age, sex and education level categories from respondents to a survey containing RA disease activity Patient-Reported Outcome Measures. The ‘think aloud’ technique was used to understand how individual items were interpreted and answered the 12 items of the item pool plus 12 additional relevant items that could potentially be included. Participants were asked about relevance, comprehensiveness, comprehensibility of the set of items overall. Reflexive thematic analysis was used to identify these broader aspects of content validity. Participants were also asked whether they could distinguish RA symptoms from those of other conditions, whether tenderness and swelling should be assessed together or separately, and whether they felt that fatigue and general health were separate issues to their disease activity. Content analysis was used for this section of the interviews. Results: Twenty participants completed one-to-one cognitive interviews between November 2022 and February 2023. No participants raised concerns relating to comprehensiveness, comprehensibility or relevance aspects of items. There was a lack of consensus on the ease of distinguishing RA symptoms from other conditions, or whether tenderness and swelling should be asked about in a single item or as separate symptoms. The majority view was that fatigue and general health were not specific to RA disease activity. Conclusion: The findings indicate that the 12-item pool adequately captures relevant concepts of RA disease activity, with no additional items required and thus provide evidence of its content validity. Future research of content validity will be needed for any new RA disease activity items.