Validity of the MACTAR questionnaire as a functional index in a rheumatoidarthritis clinical trial

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 t heir relation to RA. We evaluated MACTAR's feasibility and validity (conten t validity, construct validity, and responsiveness). Methods. A randomized trial of combined treatment in 155 patients with earl y RA; patients' mean age at baseline was 50 years and median disease durati on since diagnosis was 4 months. Results. Feasibility: MACTAR requires trained interviewers. In the trial, i nterviews took about 15 min. In longer term followup, activities selected a t baseline may become less relevant as the pattern of disability changes. F ollowup from 153 patients (99%) was available. At least 5 impaired activiti es were identified and ranked by 147 patients (95%); interviewers could fol low 99% of these. The scoring system proved complex and required amendments . Content validity: Although its main focus is physical function, the MACTA R also contains generic questions; 75% of the patients named at least one i mpaired activity from the category "mobility." Only 48% were covered by Hea lth Assessment Questionnaire (HAQ) items. Construct validity. MACTAR scores correlate highly with other functional indices and with measures of diseas e 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 instrumen t to assess change in functional ability of patients with early RA with act ive disease. It provides insight into problems - mainly of physical Functio n - that really matter to patients. For standard clinical trials and clinic al care, feasibility of the MACTAR is limited and the simpler HAQ remains t he instrument of choice.