Development and Validation of a Patient-centred Measure of Activity Limitation (MAL) in Rheumatoid Arthritis

Objective: This study sought to understand patients' experiences of activity limitation in rheumatoid arthritis (RA) to inform the development and preliminary validation of a new patient-centred assessment tool.

Methods: Interviews, focus groups and diaries provided insight into patients' experiences of change in activity limitation. These data informed item generation for the Measure of Activity Limitation (MAL) questionnaire. Postal surveys, comprising the MAL, Short Form 36 (SF36) and Health Assessment Questionnaire (HAQ), were used to inform item reduction and assess the MAL's validity, reliability and sensitivity.

Results: Qualitative exploration of activity limitation with 30 patients led to the development of a 36-item questionnaire addressing the impact of symptoms on activity, difficulty in global function and difficulty in task performance. Analysis of data from a postal survey of 168 patients led to the development of a 19-item questionnaire which demonstrated moderate correlations with the HAQ and relevant scales of the SF36. A second postal questionnaire, completed on two occasions by 308 patients, assessed test-retest reliability. One hundred and ninety-three people reporting no change in disease showed mean change in MAL score between the two completions of 0.41 [95% confidence interval (CI) -0.38 -1.22)], demonstrating test-retest reliability. Thirty-two patients reporting improvement showed a mean change of -7.84 (95% CI -11.15 to -4.54) and 83 reporting deterioration showed mean change of 4.63 (95% CI 3.09-6.16), suggesting that the MAL is sensitive to self-reported clinical change.

Conclusion: Our results suggest that the MAL is valid, reliable and sensitive to self-reported change. The MAL may provide a useful patient-centred adjunct to existing measures of activity limitation.