Psychometric properties of a new treatment expectation scale in rheumatoid arthritis: an application of item response theory

Background: Patient-generated health outcome measures are important in the assessment of long-term treatment goals for Rheumatoid Arthritis (RA), but few psychometrically sound measures are available. The MAPLe-RA (Measuring Actual Patient-Led expectations in RA) is a new questionnaire and its psychometric properties are not investigated. This study aims to examine these properties for each of the items using Item Response Theory (IRT). Methods: Participants were included if they completed the scale (MAPLe-RA). A one parameter (Rasch) model and a two parameter logistic (2PL) model were applied to these data using M-plus software. Results: One hundred thirty-eight patients with RA were included in the analysis. MAPLe-RA scale comprised of 21 items, the mean score was 71 (20.28) ranging from 0 to 105. Most items operated in the high expectations part of the items characteristics curves (ICC). Item discrimination varied widely, items with the highest discrimination capacity from the three domains were: pain (physical domain); control of my RA (self-management) and maintaining social role (psycho-social domain); feeling better overall and involvement in treatment decision making (impact of new treatment domain). Conclusion: RA patients' expectations of treatment are higher in the physical and psycho-social domains and less so in the impact of new treatment domain.