Psychometric validation of the Croatian version of the Quality of Life in Epilepsy Inventory (QOLIE-31)

The primary goals of this study were to adapt the Quality of Life in Epilepsy Inventory-31 items (QOLIE-31) questionnaire to the Croatian language and to assess the translated questionnaire's psychometric properties. Translation/retranslation of the English version of the QOLIE-31 was done, and all steps for cross-cultural adaptation process were performed properly by an expert committee. Later, QOLIE-31 questionnaires and previously validated Short Form-36 (SF-36) outcome instruments were given to 200 patients with epilepsy. 172 patients (86%) responded to the first set of questionnaires, and 114 of the first time respondents (66%) returned their second survey. The two measures of reliability as internal consistency and reproducibility were determined by Cronbach alpha statistics and intraclass correlation coefficient, respectively. Concurrent validity was measured by comparing with a SF-36 questionnaire, and measurement was made using the Pearson correlation coefficient (r). The study demonstrated satisfactory internal consistency with high Cronbach a values for all of the corresponding domains (seizure worry 0.84, medication effects 0.80, emotional well-being 0.73, energy/fatigue 0.76, cognitive functioning 0.71, social functioning 0.77, overall quality of life 0.65). The intraclass correlation coefficient for six domains of QOLIE-31 questionnaire demonstrated excellent test/retest reproducibility (ICC > or = 0.75), and good test/retest reproducibility (ICC 0.71) in one domain (cognitive functioning). Considering concurrent validity, three domains had excellent correlation (r = 0.75-1), while 11 had good correlation (r = 0.50 to 0.75), and 3 had moderate correlation (r = 0.25-0.50). This study demonstrated that, if measures are to be used across cultures, the items must not only be translated well linguistically but also must be culturally adapted to maintain the content validity of the instrument at a conceptual level across different cultures. Croatian version of QOLIE-31 will be a valuable contribution to outcome measurement in epilepsy patients, particularly in the context of treatment trials, but als in a wider research context.