To Örebro University

Objectives:  Few questionnaires have been developed and validated to specifically index insomnia-specific cognitive mechanisms. The purpose of this study was to investigate the psychometric properties of a newly developed instrument, the Insomnia Catastrophising Scale (ICS). We seek to examine the factorial validity and internal consistency, discriminative and convergent validity along with associations with anxiety, depression, sleep parameters, and daytime impairment.

Methods: Participants (n = 1803) from a randomly selected sample of the general population completed a survey that probed demographics, night-time symptoms, daytime impairment, anxiety and depression.  The ICS was also administered. Excluding those with a sleep disorder other than insomnia, the study sample consisted of 1558 participants.  

Results: Of the twenty original ICS items, three were removed due to low communality. Exploratory factor analysis of the eleven items indexing night-time catastrophising indicated a one-factor solution (59.1% variance), strong primary loadings, and high internal consistency (α = .92). Analysis of the six items indexing daytime catastrophising indicated a one-factor solution (70.1% variance), strong primary loadings, and high internal consistency (α = .91). The internal consistency for the total ICS was .95. At scale-, subscale-, and item-levels significant mean differences were noted between three groups which differed on insomnia symptomatology; the insomnia disorder group (n = 113) reported significantly higher scores than the poor sleep (n = 247) and normal sleep groups (n = 1157), and the poor sleep group exhibited significantly higher scores than the normal sleep group. Receiver operating characteristics analyses indicated that when using an optimal cut-off for the ICS, the sensitivity was 84.1% (detecting those with insomnia disorder) and specificity was 81.5% (detecting those with normal sleep). The ICS was significantly associated with anxiety and depression (ρ = .44-.54), total wake time (η = .38), total sleep time (η = .29), sleep quality (ρ = .49), and daytime impairment (ρ = .57).

Conclusion: The ICS can be considered as a reliable and valid questionnaire for indexing insomnia-specific catastrophising. The use of the ICS is recommended in research and clinical settings for assessing insomnia-related catastrophising.