The Health Assessment Questionnaire (HAQ) has become the most common tool for measuring functional status in rheumatology. However, the HAQ is long (34 questions, including 20 concerning activities of daily living and 14 relating to the use of aids and devices) and somewhat burdensome to score, has some floor effects, and has psychometric problems relating to linearity and confusing items. We undertook this study to develop and validate a revised version of the HAQ (the HAQ-II).
Using Rasch analysis and a 31-question item bank, including 20 HAQ items, the 10-item HAQ-II was developed. Five original items from the HAQ were retained. We studied the HAQ-II in 14,038 patients with rheumatic disease over a 2-year period to determine its validity and reliability.
The HAQ-II was reliable (reliability of 0.88, compared with 0.83 for the HAQ), measured disability over a longer scale than the HAQ, and had no nonfitting items and no gaps. Compared with the HAQ, modified HAQ, and Medical Outcomes Study Short Form 36 physical function scale, the HAQ-II was as well correlated or better correlated with clinical and outcome variables. The HAQ-II performed as well as the HAQ in a clinical trial and in prediction of mortality and work disability. The mean difference between the HAQ and HAQ-II scores was 0.02 units.
The HAQ-II is a reliable and valid 10-item questionnaire that performs at least as well as the HAQ and is simpler to administer and score. Conversion from HAQ to HAQ-II and from HAQ-II to HAQ for research purposes is simple and reliable. The HAQ-II can be used in all places where the HAQ is now used, and it may prove to be easier to use in the clinic.