Modelling valuations for EQ-5D health states: an alternative model using differences in valuations

Objectives. The EQ-5D is a preference-based measure of health and is increasingly being used in the evaluation of health technologies. A 'tariff' of values for all 243 EQ-5D health states has been generated using direct valuations on a subset of these states. The tariff is used to express the value of differences between health states, and so this paper explores whether a tariff with better predictive ability can be calculated using differences between values rather than using the values themselves. Methods. The original tariff (reported in this journal) was based on valuations for 42 EQ-5D states elicited from a representative sample of 2997 members of the UK general population using the time trade-off method. This same data are used to estimate a tariff based upon the differences in value between the worst possible state (33333) and all other states. Results. A simple model that fits the data well is one in which the differences in value between 33333 and all other states are explained in terms of the change in each dimension plus a term to pick up whether some dimensions change by the maximum amount whereas others do not change at all. The mean absolute difference between the actual values and those predicted by this model is 0.03 (compared with 0.039 in the original model). Conclusion. The model presented in this paper predicts the difference between 33333 and all other states remarkably well and can be used to generate a tariff for all EQ-5D health states. In fact, this model more accurately predicts the values of states for which there are direct observations, and so we recommend its comparison with the original model in evaluative studies.