Does the Stanford Health Assessment Questionnaire have potential as a monitoring tool for subjects with rheumatoid arthritis?

OBJECTIVE: To assist in the interpretation of the Stanford Health Assessment Questionnaire (HAQ) score changes for individual patients with rheumatoid arthritis (RA), by determining the minimum size of score change that can confidently be considered to reflect a significant change in disability from the patient's perspective.
METHOD: HAQ score changes were calculated for 40 clinic patients with RA who had reported no change to health in general over two months. These were considered to reflect both inconsistencies in questionnaire completion and any true but minor changes not considered significant enough by the patients to represent a change to their health in general. HAQ score changes over one year were also calculated for 207 clinic patients with RA.
RESULTS: The range within which 95% of score changes would be expected to lie in the absence of significant change was estimated as +/-0.48 points (+/-2SD of the score changes) and 80% within +/-0.31 points (+/-1.29SD). A chi(2) test showed no significant association between an HAQ score increase of >0.31 over one year and decline in health related to arthritis reported by the patient over the same period.
CONCLUSION: As a general guideline, an HAQ score needs to change by 0.48 points or more for 95% confidence that it reflects significant change (0.31 for 80% confidence). Although the value of HAQ as a group outcome measure is well established, this study questions the usefulness of monitoring individual HAQ scores in a clinical setting.