Comparison of direct and indirect methods of estimating health state utilities for resource allocation: review and empirical analysis

Abstract

Background and objective: Utilities (values representing preferences) for healthcare priority setting are typically obtained indirectly by asking patients to fill in a quality of life questionnaire and then converting the results to a utility using population values. We compared such utilities with those obtained directly from patients or the public.

Design: Review of studies providing both a direct and indirect utility estimate.

Selection criteria: Papers reporting comparisons of utilities obtained directly (standard gamble or time tradeoff) or indirectly (European quality of life 5D [EQ-5D], short form 6D [SF-6D], or health utilities index [HUI]) from the same patient.

Data sources: PubMed and Tufts database of utilities.

Statistical methods: Sign test for paired comparisons between direct and indirect utilities; least squares regression to describe average relations between the different methods.

Main outcome measures: Mean utility scores (or median if means unavailable) for each method, and differences in mean (median) scores between direct and indirect methods.

Results: We found 32 studies yielding 83 instances where direct and indirect methods could be compared for health states experienced by adults. The direct methods used were standard gamble in 57 cases and time trade off in 60(34 used both); the indirect methods were EQ-5D (67 cases), SF-6D (13), HUI-2 (5), and HUI-3 (37). Mean utility values were 0.81 (standard gamble) and 0.77 (time tradeoff) for the direct methods; for the indirect methods: 0.59(EQ-5D), 0.63 (SF-6D), 0.75 (HUI-2) and 0.68 (HUI-3).

Discussion: Direct methods of estimating utilities tend to result in higher health ratings than the more widely used indirect methods, and the difference can be substantial.Use of indirect methods could have important implications for decisions about resource allocation: for example, non-lifesaving treatments are relatively more favoured in comparison with lifesaving interventions than when using direct methods.

Fig 1 Direct versus indirect methods of utility elicitation See Brazier et al, 1999.

Fig 2 Bland-Altman plot comparing direct and indirect utilities for average health states within independent groups of participants. Vertical axis represents half the difference in utilities; horizontal axis is the average of the two utilities. Broken lines enclose the feasible region for utilities constrained to lie between 0 and 1. The single point outside this region represents a state with a negative EQ-5D estimate.

Fig 3 Direct utilities against indirect utilities. Plotted points are means (if available) or medians from health-states within 28 studies. Vertical and horizontal lines represent standard errors cited (or deduced) within the studies. Broken lines are regressions of direct on indirect utilities from current patient comparisons. In top left panel, one (hypothetical) point lies off the scale, with EQ-5D=−0.52, time trade off=−0.17.