Validity and discriminant ability of the HAQ Functional Index in early rheumatoid arthritis

A sensitive and valid instrument is needed in the earliest stages of rheumatoid arthritis (RA) for the measurement of functional disability. A French version of the Health Assessment Questionnaire Functional Disability Index (HAQ) has been developed, validated in an early RA sample (i.e. with disease duration less than 5 yr; n = 50), and compared with longstanding RA (n = 32) and control subjects (n = 59). Five factors provided by principal components analysis accounted for 75% of the variability of the HAQ score (construct validity). It appeared to be significantly correlated with clinical and radiological variables and to be reproducible (r intraclass = 0.964). It proved to be discriminant in groups with various levels of disability (HAQ score = 1.332 in early RA, 1.745 in longstanding RA, and 0.152 in controls; p less than 10(-5). Finally, the validity of the original scoring method of the HAQ, as compared with other scoring methods, was confirmed.