Minimally important difference of Health Assessment Questionnaire in psoriatic arthritis: relating thresholds of improvement in functional ability to patient-rated importance and satisfaction

Philip J Mease, J Michael Woolley, Bojena Bitman, Brian C Wang, Denise R Globe, Amitabh Singh
Journal of Rheumatology 2011, 38 (11): 2461-5

OBJECTIVE: To evaluate changes in function as measured by Health Assessment Questionnaire Disability Index (HAQ-DI) and the meaningfulness of the changes, in importance and satisfaction, in patients with psoriatic arthritis (PsA).

METHODS: HAQ-DI was assessed at baseline and at Weeks 4, 12, and 24 in a randomized double-blind study of 205 patients with active PsA receiving etanercept 25 mg twice weekly or placebo. Concurrently, patients rated the importance of and satisfaction with their change in function on a 7-point scale (1 = not at all important/satisfied; 7 = extremely important/satisfied). Mean HAQ-DI improvement corresponding to ratings of minimally (2-3) or very (6-7) important or satisfied was determined using a posthoc linear mixed-model analysis. Patient importance ratings were used as an anchor to estimate minimally important difference (MID) for HAQ-DI; distribution-based estimates were also calculated.

RESULTS: A total of 161 patients (69 placebo; 92 etanercept) had ≥ 1 HAQ-DI scores showing improvement from baseline and a corresponding importance or satisfaction rating. HAQ-DI improvements corresponding to importance scale ratings of 2 or 3 were 0.335 (95% CI 0.214, 0.455) and 0.360 (95% CI 0.263, 0.456), respectively, suggesting an MID of about 0.35. HAQ-DI improvements corresponding to satisfaction scale ratings of 2 and 3 were 0.293 (95% CI 0.230, 0.357) and 0.360 (95% CI 0.307, 0.413). For a given change in HAQ-DI, nearly two-thirds of patients indicated a lower rating for satisfaction than for importance. This trial was registered in the registry (NCT00317499).

CONCLUSION: Our study suggests the MID for HAQ-DI in PsA is about 0.35. The results may also provide insight into patient satisfaction with changes in function and expectations for therapy.

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