Properties of the 15D and EQ-5D utility measures in a community sample of people with epilepsy.

To perform economic evaluation studies in epilepsy using utilities, such as cost-utility analyses, it is necessary to have reliable and valid instruments for eliciting people's preferences. The objective of this study was to assess the reliability and validity of two multiattribute utility measures in a community sample of 397 people with epilepsy. We assessed the test-retest reliability of individual questionnaire items and aggregate scores. Additionally, construct validity was assessed by correlating items of the EQ-5D with items of the 15D health status questionnaire, and discriminant validity was assessed by comparing scores for known groups. The test-retest reliabilities for the individual items of the 15D (weighted kappa 0.59-0.90, except mobility with only 0.28) and the EQ-5D (weighted kappa 0.49-0.86) were acceptable. For the composite utility scores the test-retest reliability was better (intraclass correlation coefficient 0.93 for both 15D and the EQ-5D). Spearman's rank correlations between EQ-5D single item scores and corresponding 15D single item scores were high (rho 0.34-0.79) and generally higher than the associations between non-corresponding items. Some EQ-5D and 15D items discriminated well between patients according to seizure status, psychiatric comorbidity and working status; less well after antiepileptic drug use and neurologic comorbidity. Both the EQ-5D and 15D were reliable instruments and showed properties supporting the construct validity of both measures.