Morningness-eveningness dimension: is it really a continuum?

Several self-evaluation instruments have been developed for identifying the individual circadian typology. The use of these instruments suggests the idea that the morningness-eveningness dimension could be considered as a continuum between two extremes. Aim of the present work is to support such an idea by means of external criteria. A sample of 222 subjects was administered the Morningness-Eveningness Questionnaire (MEQ). Six typologies were considered: definitely morning, moderately morning, intermediate-morning, intermediate-evening, moderately evening, and definitely evening. Body temperature, and subjective alertness readings were collected at 08:00, 14:00, and 23:00 in counterbalanced order. As regards subjective alertness a significant interaction (ANOVA) between circadian typology and time of day was found. At 08:00 the recorded values of subjective alertness gradually increased starting from the definitely evening extreme typology to the definitely morning one, vice-versa at 23:00. These results seem to support the idea that the morningness-eveningness dimension could be considered as a continuum between two extremes: morning-evening preference. Nevertheless, this is especially true for subjective alertness. Suggestions about how to use the MEQ are put forward.