Avoiding double-counting in pharmacoeconomic studies.

In cost-utility analyses of pharmaceutical treatments, the costs are measured in monetary terms and the effects are measured as quality-adjusted life years (QALYs) gained. QALYs are constructed by assigning life years a quality weight between 0 (dead) and 1 (full health). A potential problem in cost-utility analysis is that some consequences, in principle, can be included both in the costs and in the quality adjustment, which can lead to double-counting. This article outlines the double-counting problem in cost-utility analysis. It shows that the potential for double-counting depends on how healthcare and income losses resulting from disease are financed, and on how the questions that assess the quality weights are phrased. Double-counting can be avoided by telling respondents to assume that healthcare costs and income losses are fully reimbursed when quality weights are assessed. The quality weights would then capture the change in health and leisure, and the other consequences could be included in the cost estimation.