The sleep of 'morning' and 'evening' types.

A questionnaire developed by Ostberg to differentiate 'morning' types from 'evening' types was administered to 100 college students. The actual sleep behavior of the 11 extreme 'morning' types (larks) and the 10 extreme 'evening' types (owls) was monitored for two weeks with a sleep log and the Post-sleep Inventory. Data was collected from the owls for a further two-week period in which the owls had been instructed to attempt to arise at the lark arousal time. In addition to going to bed earlier and getting up earlier than the owls, the larks had a less variable sleep length and awakening time and took shorter naps than the owls. Larks further reported fewer physical problems and less mental activity across the night as well as more adequate sleep than owls, who differed little from the normal college population even after having their awakening time shifted.