Validation of the full and reduced Composite Scale of Morningness

Different self-report scales have been designed and developed to measure circadian preferences and there are attempts to develop shorter scales for research. The main aims of the present study were to provide further evidence for the validity of the full Composite Scale of Morningness (CSM), second, to develop a short scale of the CSM, and third, provide evidence for the short scale (rCSM). The full CSM was validated externally by self-report physical and cognitive peak performance, self-reported sleep-wake rhythm, and correlation with midpoint of sleep. Based on inter-item correlations and factor analysis, the final short scale was composed of Items 1, 2, 5, 6, 9, 10, 12 and labelled reduced CSM (rCSM). The rCSM contains two five-point-Likert items and five four-point-Likert items, and, thus, it ranges from 7 to 30 points as a possible total score. First analyses suggest a two factor structure. The rCSM showed good correlations with self-reported sleep-wake rhythm, midpoint of sleep, personality (conscientiousness) and the Morningness-Eveningness Questionnaire (MEQ). The scale was stable over approximately three months and was validated by subjective alertness ratings. The data obtained here suggest that the CSM in its full and reduced version is a valid instrument to assess circadian preference in both adult and adolescent samples.