Changes in quality of life in epilepsy: How large must they be to be real?

Purpose: The study goal was to assess the magnitude of change in generic an d epilepsy-specific health-related quality-of-life (HRQOL) instruments need ed to exclude chance or error at various levels of certainty in patients wi th medically refractory epilepsy. Methods: Forty patients with temporal lobe epilepsy and clearly defined cri teria of clinical stability received HRQOL measurements twice, 3 months apa rt, using the Quality of Life in Epilepsy Inventory-89 and -31 (QOLIE-89 an d QOLIE-31), Liverpool Impact of Epilepsy, adverse drug events, seizure sev erity scales, and the Generic Health Utilities Index (HUI-III). Standard er ror of measurement and test-retest reliability were obtained for all scales and for QOLIE-89 subscales. Using the Reliable Change Index described by J acobson and Truer, we assessed the magnitude of change required by HRQOL in struments to be 90 and 95% certain that real change has occurred. as oppose d to change due to chance or measurement error. Results: Clinical features, point estimates and distribution of HRQOL measu res, and test-retest reliability (all >0.70) were similar to those previous ly reported. Score changes of +/- 13 points in QOLIE-89, +/- 15 in QOLIE-31 , +/-6.3 in Liverpool seizure severity-ictal, cll in Liverpool adverse drug events, +/-0.25 in HUI-III, and +/-9.5 in impact of epilepsy exclude chanc e or measurement error with 90% certainty. These correspond, respectively, to 13, 15, 17, 18, 25, and 32% of the potential range of change of each ins trument. Conclusions: Threshold values for real change varied considerably among HRQ OL tools but were relatively small for QOLIE-89, QOLIE-31, Liverpool Seizur e Severity, and adverse drug events. In some instruments, even relatively l arge changes cannot rule out chance or measurement error. The relation betw een the Reliable Change Index and other measures of change and its distinct ion from measures of minimum clinically important change are discussed.