In a previous study comparing two representative chronotype questionnaires to screen for delayed sleep-phase disorder, six items from the simplified language version of Composite Scale of Morningness (CSM) have been found to be useful and effective for screening evening-type person. In this study, we reverse coded the six items from CSM and named them Evening Chronotype Scale (ECS). The primary aim of this study was to examine the psychometric properties, validity, and test-retest reliability of the ECS when administered on mood disorder patients. The secondary aim was to further examine the relationship between circadian preferences and symptoms of mood disorders. The study sample was of 472 mood disorder patients including major depressive disorder, bipolar disorder I, and bipolar disorder II. The 13-item full version CSM and 6-item ECS were externally validated by self-reported sleep time, wake time, sleep latency, depressive symptoms, hypomanic symptoms, quality of life, and impulsivity. Cronbach's alpha was calculated for the internal consistency of the ECS, and the test-retest reliability analysis was also performed. Our results suggest that the ECS is a reliable and valid instrument to assess circadian preference in mood disorder patients. First, the ECS showed moderate to good internal consistency (Cronbach's alpha = 0.727). Also, it showed external validity comparable to that of the 13-item CSM. Participants who were more evening-oriented according to the ECS slept and woke up later, took longer time to fall asleep, showed more depressive and hypomanic symptoms, and showed lower quality of life and higher impulsivity. As circadian rhythm disruption has been shown to affect the regulation of mood symptoms in patients with mood disorders, assessment of circadian preferences may be crucial in clinical settings. We suggest that ECS appears to be an easy-to-use instrument that is reliable and valid.
Keywords: Chronotype; circadian preference; eveningness; mood disorder; questionnaire; validation.