Health Assessment Questionnaire modifications: is standardisation needed?

BACKGROUND Physical disability is part of the end point measures in rheumatoid arthritis clinical trials. The Stanford Health Assessment Questionnaire Disability Index (HAQ DI) is often used for this purpose but lacks international uniformity owing to variations in the translated and adapted questionnaires and variations in its calculation. To study the consequences of these variations the previous Dutch HAQ (HAQ90) was revised, resulting in a new Dutch HAQ (HAQ99). OBJECTIVE To compare DI scores from the two versions, and to study the consequences of applying different calculation methods for the DI score. METHODS 78 patients completed both the HAQ99 and the HAQ90. To compare the use of different category score calculation methods a post hoc analysis on prospectively collected data obtained in clinical trials was performed. RESULTS No statistically significant differences were observed between the DI scores of the HAQ90 and the HAQ99 using the alternative method (that is, without correcting for aid and devices). However, correcting for the use of aid or devices or not did result in statistically significant different DI scores. The systematic shift when using the maximum or mean item score for calculation of the category score resulted in non-comparable absolute DI scores. CONCLUSION The use of HAQ DI questionnaires with different numbers of items and/or categories does not hinder international comparability, except when these variations interfere with the calculation method of the DI (as in the case of questionnaires without a section correcting for devices). For the sake of international uniformity the HAQ or any validated translation should be used and calculated in a standard way, including correcting for the use of aid and devices, and taking the maximum within each category as the category score.