There is more to chronotypes than evening and morning types

Evidence is accumulating for the possibility to distinguish more than two distinct chronotypes, i.e., people would be neither morning nor intermediate nor evening types. We tried to establish four-type division into distinct chronotypes without implying any chronotypological questionnaire. A community-based online survey (n = 1305) included a visuo-verbal judgment task for evaluating how sleepy a survey participant thinks he/she would be at different randomly presented times. We predicted that principal component (PC) analysis of 24-h sleepiness curves would yield more than one PC. Consequently, only two types based on PC score would be sleepy in the evening but not in the morning (morning type) and in the morning but not in the evening (evening type), while two other types would be sleepy both in the morning and in the evening and neither in the morning nor in the evening. Results of PC analysis yielded four PCs with the predicted loading patterns. Four distinct patterns of sleepiness curves were identified by dividing participants in accord with scores PC > 1, −1 < PC < 1, and PC < −1. Only 396 participants were of intermediate chronotype (−1 < PC1–PC4 < 1) with a similar to the sample-averaged sleepiness curve, while, like morning and evening types, two further types (named “afternoon” and “napper”) were not uncommon.