Quality of life measures in epilepsy - How well can they detect change over time?

Objective: To evaluate the ability of health-related quality of life (HRQOL ) measures to detect change over time in persons with epilepsy. Background: The application of HRQOL measures in clinical trials has been limited by a dearth of information regarding their abilities to measure change over tim e (i.e., their responsiveness). To calculate responsiveness, one must categ orize subjects as "changed" or "unchanged" by a priori criteria. Methods: T he authors analyzed data collected at baseline and at 28-week follow-up fro m an antiepileptic drug trial. Two different criteria for classifying subje cts as changed or unchanged-one based on seizure frequency (where changed = attainment of seizure freedom) and one based on self-reported overall cond ition (where changed = improvement in overall condition)-were used. We comp ared responsiveness indices for two generic (Short Form [SF]-36 and SF-12) and two epilepsy-targeted (Quality of Life in Epilepsy [QOLIE]-89 and QOLIE -31) HRQOL measures. Two scoring procedures for the SF-36, one based on cla ssic test theory and the other on item response theory (IRT), were compared . Results: Effect sizes of the most responsive HRQOL measures were medium t o large. The shorter epilepsy-targeted measure had similar responsiveness i ndices to those of the longer measure. Epilepsy-targeted measures were cons istently more responsive than generic measures under the overall condition criterion, but for the seizure freedom criterion, IRT scoring of the SF-36 yielded responsiveness indices comparable to those of the epilepsy-targeted measures. Conclusion: Epilepsy-targeted health-related quality of life mea sures may be preferable to generic ones in longitudinal studies. Selection of a shorter epilepsy-targeted measure does not compromise responsiveness. Item response theory scoring should be applied to epilepsy-targeted HRQOL m easures.