Quality of life in epilepsy: comparison of four preference measures

Several specific and general measures are available for the assessment of overall health related quality of life in epilepsy. Few of the commonly used measures provide utility weights for use in cost-utility analyses. This study compares four methods for measuring utility weights: time trade-off (TTO), standard gamble (SG), 15D, end the EuroQol visual analog scale. All patients aged 18-67 years with a diagnosis of epilepsy, who had been admitted to or attended the outpatient clinic at a large county hospital 1987-1994, received a comprehensive questionnaire. From 397 respondents, 82 patients were randomly selected. Most of the 57 patients completing the study generally had well-controlled epilepsy, but were still on anti-epileptic medication. Mean age was 44 years. Fourty-one percent were male and 59% female. The resulting utility weights differed considerably between the measures, both with regard to central tendency and dispersion. Median utility scores: EuroQol visual analog scale 0.75, 15D 0.90, TTO 0.98, SG 0.99. There was a good association between the EuroQol rating scale and the 15D, and a moderate association between SG and TTO. These preference instruments measure different aspects of health-related quality of life and thus yield different results. Caution should be taken when interpreting cost-utility studies, as results will depend on the choice of utility instrument.