Roughly right or precisely wrong? Systematic review of quality-of-life weights elicited with the time trade-off method.

OBJECTIVE

Cost-utility analysis is gaining importance as a tool for setting priorities in health care. The approach requires quality-of-life weights on a scale from 0.00 (corresponding to death) to 1.00 (corresponding to perfect health). Different methods and perspectives of the evaluators tend to give different results. Time trade-off (TTO) is the most commonly used method to elicit quality-of-life weights for quality-adjusted life-years (QALYs). How reliable are the results of this method, when limited to one specific perspective, as input for cost-utility analysis?

METHOD

Systematic literature review of empirical studies in which the TTO is elicited by the respondent on their own behalf.

RESULTS

In 56 papers, quality-of-life weights for 102 diagnostic groups were given. Ranking of the diagnostic groups according to their quality-of-life weights had no apparent relation to severity. One specific diagnostic group was assigned quality-of-life weights ranging from 0.39 to 0.84. Altogether, 57% of respondents did not trade any life-time at all in exchange for health improvements. The distributions studied were skewed towards 1.00 and were bimodal without a central tendency. The correlation between the TTO and related methods was generally weak. Possible explanations for the poor empirical properties of the TTO are inappropriate use of the method, lack of representative samples, or that the TTO does not measure what it claims to measure.

CONCLUSION

In the light of these findings, the TTO elicited from the patient perspective, as currently practised, should not be used as an input for QALYs or for comparisons of diagnostic groups.