Psychometric properties of the Japanese version of the Insomnia Catastrophizing Scale and relationship of insomnia severity with catastrophic thoughts, safety behaviors, and dysfunctional beliefs

Background: This study aimed to clarify the reliability and validity of the Japanese version of the Insomnia Catastrophizing Scale (ICS) and to examine the relationship between insomnia severity and insomnia-related cognitive factors. Methods: A total of 786 participants were recruited via an online survey and classified into the insomnia group (n = 342) and healthy group (n = 444). The insomnia group comprised individuals who self-reported meeting the diagnostic criteria for chronic insomnia disorder in the third edition of the International Classification of Sleep Disorders. Results: The ICS is used to independently assess nighttime (ICS-N) and daytime (ICS-D) catastrophic thoughts, and item response theory revealed that each ICS-N and ICS-D item can adequately assess catastrophic thoughts during the night and day, respectively. The internal consistency and test-retest reliability of the ICS-N and ICS-D were good. Further, the ICS-N and ICS-D had a significant positive correlation with insomnia severity, hyperarousal, sleep-related safety behaviors, dysfunctional beliefs about sleep, and anxiety symptoms. Multiple regression analyses with insomnia severity as the dependent variable in the insomnia group demonstrated that catastrophic thoughts were more strongly associated with insomnia severity than sleep-related safety behaviors and dysfunctional beliefs about sleep. The interaction between nighttime catastrophic thoughts and sleep-related safety behaviors increased insomnia severity. Conclusions: The Japanese versions of ICS-N and ICS-D were found to be superior in measuring insomnia-related catastrophic thoughts and to have high reliability and validity. Furthermore, these findings more clearly demonstrate that the catastrophic thoughts may be an important associated factor of insomnia.