Variation in the apparent importance of health-related problems with the instrument used to measure patient welfare.

Different instruments give prominence to different physical and psycho-social problems and consequently favour different groups of patients. Budgetary decisions which appear to be based on efficiency criteria such as the cost per quality-adjusted life year (QALY) conceal distributive effects attributable to the instrument used in the analysis. The effects are additional to the ethical questions considered in making an equity-efficiency trade-off as they arise from the measurement of efficiency.