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AbstractPurpose Different health state utility (HSU) instruments produce different utilities for the same individuals, thereby compromising the intended comparability of economic evaluations of health care interventions. When developing crosswalks, previous studies have indicated non-linear relationships. This paper inquires into the degree of non-linearity across the four most widely used HSUinstruments, and proposes exchange rates that differ depending on the severity levels of the health state utility scale.Method Overall, 7933 respondents from six countries; 1760 in a non-diagnosed healthy group and 6173 in seven disease groups, reported their health states using four different instruments: EQ-5D-5L, SF-6D, HUI-3 and 15D. Quantile regressions investigate the degree of non-linear relationships between these instruments. To compare the instruments across different disease severities, we split the health state utility scale into utility intervals with 0.2 successive decrements in utility starting from perfect health at 1.00. Exchange Rates (ERs) are calculated as the mean utility difference between two utility intervals on one HSU-instrument divided by the difference in mean utility on another HSU-instrument.Result Quantile regressions reveal significant non-linear relationships across all four HSUinstruments. The degrees of non-linearities differ, with a maximum degree of difference in the coefficients along the health state utility scale of 3.34 when SF-6D is regressed on EQ-5D. At the lower end of the health state utility scale, the exchange rate from SF-6D to EQ-5D is 2.19, whilst at the upper end it is 0.35.
ConclusionComparisons at different utility levels illustrates the fallacy of using linear functions as crosswalks between HSU-instruments. The existence of non-linear relationships between different HSU-instruments suggests that level-specific exchange rates should be used when converting a change in utility on the instrument used, onto a corresponding utility change had another instrument 3 been used. Accounting for non-linearities will increase the validity of the comparison for decision makers when faced with a choice between interventions whose calculations of QALY-gains have been based on different HSU-instruments.