Validity of the MACTAR questionnaire as a functional index in a rheumatoid arthritis clinical trial. The McMaster Toronto Arthritis

Abstract

Objectives: The McMaster Toronto Arthritis patient preference questionnaire (MACTAR) is a functional index that measures change in impaired activities selected by each patient in a baseline interview, and change in rheumatoid arthritis (RA) disease activity. In addition, it contains questions on the state of physical, social and emotional function and overall health, and their relation to RA. We evaluated MACTAR's feasibility and validity (content validity, construct validity, and responsiveness).

Methods: A randomized trial of combined treatment in 155 patients with early RA; patients' mean age at baseline was 50 years and median disease duration since diagnosis was 4 months.

Results: Feasibility: MACTAR requires trained interviewers. In the trial, interviews took about 15 min. In longer term followup, activities selected at baseline may become less relevant as the pattern of disability changes. Followup from 153 patients (99%) was available. At least 5 impaired activities were identified and ranked by 147 patients (95%); interviewers could follow 99% of these. The scoring system proved complex and required amendments. Content validity: Although its main focus is physical function, the MACTAR also contains generic questions; 75% of the patients named at least one impaired activity from the category "mobility." Only 48% were covered by Health Assessment Questionnaire (HAQ) items. Construct validity: MACTAR scores correlate highly with other functional indices and with measures of disease activity. Responsiveness: At 16 weeks the standardized response mean for the total MACTAR score in the combined-treatment group was excellent, at 2.2. Items that directly address change were even more responsive.

Conclusion: The MACTAR interview is a valid and highly responsive instrument to assess change in functional ability of patients with early RA with active disease. It provides insight into problems--mainly of physical function--that really matter to patients. For standard clinical trials and clinical care, feasibility of the MACTAR is limited and the simpler HAQ remains the instrument of choice.