Division of Rheumatology, Department of Medicine, University Health Network and 1 Scleroderma Clinic, Mount Sinai Hospital, University of Toronto, Canada
Correspondence to: S. R. Johnson, Toronto Western Hospital, Division of Rheumatology, Edith Cavell Wing S-028, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada. E-mail: sindhuj{at}uhnres.utoronto.ca
SIR, Sultan et al. describe the predictive validity of the health assessment questionnaire disability index (HAQ-DI) in scleroderma patients [1]. They suggest that the HAQ-DI should be included as a routine outcome measurement in future scleroderma clinical trials. There are a number of operational issues pertaining to this index, however, that future investigators should be aware of before doing so.
First, the greatest threat to the validity of the HAQ-DI in scleroderma patients is the lack of a clear conceptual framework. Although Fries et al. used the term disability in the title of the index, subsequent investigators have failed to define their concept of disability in scleroderma, resulting in studies using the terms functional impairment, functional status, functional limitation and disability interchangeably [27]. Future investigators should clearly delineate the conceptual framework of the functional outcome they are using the HAQ-DI to measure [8].
Secondly, the HAQ was copyrighted to ensure that it would be used unmodified to preserve the validity of its results and standardize assessments across studies. The original HAQ-DI is composed of eight categories of functional activity (dressing, arising, eating, walking, hygiene, reach, grip, and common daily activities), each of which has at least two component questions, adding up to 20 items. Although often used by itself, the HAQ-DI is also used in conjunction with the VAS Pain Scale and the VAS Patient Global [9]. Despite the copyright, there have been a number of variations in the way the HAQ-DI is used. Some investigators have elected to omit the VAS Pain Scale or VAS Patient Global, while others omit the question pertaining to the use of aids or devices. Sultan et al. refer to the penicillamine trial which used the HAQ-DI without the VAS Pain Scale, whereas the methotrexate trial used the HAQ-DI with the VAS Pain Scale [10, 11]. Future investigators should ideally use the original HAQ-DI as it was intended. However, if modifications are being made, they should be clearly outlined.
Thirdly, there are alternative methods for scoring the HAQ-DI. The scoring rules permit the scoring of two disability indices: the Standard Disability Index, which takes into account the use of aids and devices; and the Alternative Disability Index, which does not [9]. Investigators often do not specify which method is being used [4, 12]. Future investigators should clearly delineate the method used to obtain the aggregate score.
Despite good predictive validity, the HAQ-DI can provide meaningful results in scleroderma clinical trials only if the concept being measured is clearly defined, the instrument being used is clearly identified, and the scoring method is described. Future investigators should keep these issue in mind when selecting the HAQ-DI as a functional outcome measure.
SRJ has been awarded a research fellowship from the Institute for Musculoskeletal Health and Arthritis (IMHA) and the Arthritis Society of Canada. PL has declared no conflicts of interest.
References
|