Psychometric properties of the Bulgarian version of the Quality of Life in Epilepsy Inventory (QOLIE-31).

The purpose of the present study was to evaluate the psychometric properties of the Bulgarian version of the Quality of Life in Epilepsy Inventory (QOLIE-31). After a translation and cultural adaptation into Bulgarian of the US version of the QOLIE-31, the reliability and construct validity of the questionnaire were assessed in 106 adults with epilepsy. After a neurological assessment, all eligible patients were enrolled consecutively from an unselected patient population and completed the QOLIE-31. As part of the same study, they were screened for comorbid depressive disorder according to the ICD-10 diagnostic criteria and evaluated on the Hamilton Depression Rating Scale (HAMD-17). Reliability was tested both by assessing internal consistency and by the test-retest method. Construct validity was tested by factor analysis and multitrait/multi-item analysis (MAP-R) and the known-group comparison validation. Validity testing was completed by analysis of variance (ANOVA) for the QOLIE-31 scores against external measures (demographic and clinical variables). The domains showed high internal consistency (Cronbach's α: 0.78-0.97; 0.95 for the overall score). Test-retest reliability was good (an intraclass correlation coefficient ranging from 0.59 to 0.94 and a Pearson's coefficient ranging from 0.64 to 0.94). Item-scale correlations were high for all domains although exploratory factor analysis did not reach solutions that exactly matched those obtained from originally designed domains. All QOLIE-31 dimensions were sensitive to the tested demographic and clinical variables, except for Medication effects (sensitive to sex). Discriminative validity was demonstrated by the difference in QOLIE-31 scores between patients with different seizure frequencies, employment status, educational levels, and depression scores. The Bulgarian version of the QOLIE-31 questionnaire is reliable and valid for assessing the quality of life of patients with epilepsy.