Mapping from the Health Assessment Questionnaire to the EQ-5D: The Impact of Different Algorithms on Cost-Effectiveness Results

Background: Many algorithms exist for converting the Health Assessment Questionnaire (HAQ) score to utility in rheumatoid arthritis (RA). Different algorithms convert the same HAQ score to different utility values, and could therefore lead to different cost-effectiveness results. Objective: To investigate the impact of different mapping algorithms within the same cost-effectiveness model. Methods: We rebuilt an existing economic model that had previously been used for estimating the cost-effectiveness of second-line biologics in RA. We reviewed the literature to identify algorithms that converted the HAQ score to utility and incorporated them into the model. We compared the costeffectiveness results using different algorithms, exploring the reasons behind the different results and the potential effect on reimbursement decisions. Results: We identified 24 different algorithms that estimated utility on the basis of the HAQ score, age, sex, and pain. 'The incremental cost-effectiveness ratio for rituximab versus diseasemodifying antirheumatic drugs varied between E18,407/qualityadjusted life year and 32,039/quality-adjusted life year, which we speculate could have changed the recommendations made by the National Institute for Health and Care Excellence. Conclusions: Using different algorithms to convert the HAQ score to utility affects the costeffectiveness of second-line biologics for the treatment of RA Using different algorithms in economic modeling for RA could lead health technology assessment bodies to make different reimbursement decisions.