Turkish adaptation and psychometrics properties of Insomnia Catastrophizing Scale

Objective: In this study, we aimed to adapt the 17-item Insomnia Catastrophizing Scale (ICS) into Turkish and to examine its psychometric properties. Method: 240 healthy volunteers and 75 patients with major depressive disorder participated in the study. The construct validity of the scale was carried out by exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) methods. For reliability analysis, Cronbach alpha coefficient, test-retest correlation and item-total correlation methods were used. ICS and subscale scores were compared between groups for discriminant validity. For assessing the criterion related validity, the Pittsburg Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI) were used. Results: The mean age of the healthy volunteers and depression group were respectively 21.29 +/- 2.88, 33.98 +/- 10.14. ICS was found to have a two-factor structure as revealed by principal component factor analysis with Varimax rotation. In the EFA, the 4th and the 11th items were included in both factors and the difference between the factor loads was less than 0.1, and the 3rd, 5th and 14th items were excluded from the scale due to the correlated errors with other factors in the CFA. The fit indices of the 12-item final version of the ICS were CMIN=135.270, df=51, p< 0.001, x(2)/df=2.652, RMSEA=0.073, CFI=0.978, GFI=0.929. The Cronbach alpha coefficients of the ICS final version, night and, daytime subscales were 0.958, 0.941 and, 0.955 respectively. Test-retest reliability analysis at two weeks also showed good temporal stability (depression group r=0.592, healthy volunteers group r=0.857). In the discrimanant validity, ICS scores were found to be significantly higher in the depression and clinical insomnia groups. Significant positive correlations were found between ICS and the PSQI and ISI. Conclusion: The ICS is valid and reliable for Turkish languge and culture with revised model as two subscale and 12 items.