Psychometric Properties of the Insomnia Severity Index in Turkish Sample

Abstract

Objective: Prevalence of insomnia was detected approximately one third of normal population in surveys. Research evidence suggests that comorbid sleep problems in patients with psychiatric disorders and health problems are not rare. Therefore, the importance of development and using of the instruments that assess primary and secondary insomnia increases. Insomnia Severity Index (ISI) developed by Morin has translated into various languages and have prevalent use for the research purposes. The aim of the study was to assess psychometric properties of the Insomnia Severity Index in Turkish sample. Methods: Data were collected from 34 patients diagnosed with depression in psychiatry clinics of Yuzuncu Yil University Faculty of Medicine Research Hospital and 258 undergraduate healthy controls. The ISI, the Hamilton Depression Scale (HDS), the Beck Depression Inventory (BDI), and Pittsburgh Sleep Quality Index (PSQI) were administered to the subjects. Concurrent validity was evaluated by calculating correlations between the ISI scores and other psychological variables. Item analyses, inner consistency coefficient and intraclass correlations between two repeated applications in both patient and healthy subjects were calculated. Construct validity was tested by using principal component analysis with varimax rotation and structural equation analysis. Results: Correlations between the instrument and other psychological variables were adequate. Item discriminations were higher than 0.44. Inner consistency of the scale was 0.79. Intraclass correlation at 30-day time interval in depressive patients was 0.65 and at 15-day time interval in 68 healthy controls was 0.82. It was found in factor analyses that Turkish form has a two-factor structure: 'Daily functionality' and 'sleep quality'. Conclusion: The ISI revealed adequate validity and reliability to be used by researchers in Turkish sample. Current results were discussed under the previous findings and concerning theoretical considerations. (Anatolian Journal of Psychiatry 2010; 11:248-252)