A new study in Personality and Individual Differences suggests there are four types of preferred sleep schedules.
In addition to "night owls" and "morning larks," researchers have identified two other types of sleep patterns: "High energetic," or people who are alert from the early morning to late at night, and "lethargic," those who are sleepy in both the morning and evening.
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Researchers at the Siberian Branch of the Russian Academy of Sciences observed 130 people in a lab, depriving them of sleep for 24 hours and surveying them about their sleep patterns, how they felt, and how well they functioned the week prior.
They found 29 larks, defined as more energetic at 9 a.m. than at 9 p.m., and 44 owls, who reported the reverse and went to sleep an average of two hours later than larks did.
But they also discovered 25 high energetic and 32 lethargic individuals. These two groups both tended to wake up and go to sleep at some time in between when the larks and owls did, but the energetic group slept an average 7.5 hours, about 30 minutes less than the other groups did (Khazan, The Atlantic, 11/11).