The relationship of medical, demographic and psychosocial factors to direct and indirect health utility instruments in rheumatoid arthritis

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Abstract
Objectives. Cost-effectiveness analysis (CEA) is essential for the comparison of treatments for rheumatoid arthritis (RA). CEA centres on accurate measurement of health utility (HU) preferences. Direct measures of HU in RA patients demonstrate weaker correlations with health status (functional disability and pain) than indirect measures. We examined whether demographic and psychosocial factors relate to HU in RA patients. Methods. HU was measured for 142 RA patients (76% women; mean age 58.75 yr) directly through standard gamble (SG) and time trade-off (TTO), and indirectly on the EuroQol (EQ-5D). Current pain (100 mm visual analogue scale) and recent functional disability (Health Assessment Questionnaire; HAQ) were assessed. A subsample of 48 provided demographic and psychosocial information (education, employment, marital/family status, knowledge about RA, medication beliefs, desirable responding, social support, optimism, and the Hospital Anxiety and Depression Scale; HADS). Results. Direct HU had higher means (SG = 0.88, TTO = 0.86) than indirect HU (EQ-5D = 0.52). HAQ functional disability correlated with SG (r = − 0.28), TTO (r = − 0.31) and EQ-5D (r = − 0.67). Current pain correlated with TTO (r = − 0.19) and EQ-5D (r = − 0.36). HADS depression correlated with TTO (r = − 0.35) and EQ-5D (r = − 0.64); HADS anxiety also correlated with EQ-5D (r = − 0.46). Conclusions. Demographic and psychosocial factors cannot completely explain either the significant differences between direct and indirect HUs in RA patients or the moderate correlations of direct HUs with health status. Characteristics of the SG and TTO may make them inappropriate for HU assessment and CEA among RA patients.