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If you never felt you quite fit into the "morning person" or "evening person" mold, you may have been on to something. New research published in the journal and Individual Differences identifies two new personality types to describe people's level of alertness throughout the day. The researchers call them the "napper" and "afternoon" chronotypes.

To come to this conclusion, a team of sleep experts from Russia and Belgium asked 1,305 people to take part in a short online survey. In the survey, participants were randomly shown different times of the day (e. ., 8 a.m., 11 p.m., 4 p.m., etc.) and were asked to predict their level of alertness/sleepiness at that time. In responding to these questions, participants were told to assume they had a normal night's sleep ending in "spontaneous waking or by a waking up signal at approximately 7:30 a.m." Further, participants were asked a series of demographic and sleep-related questions, including questions that measured their habitual sleep times and the quality of their sleep.

Here's what the researchers found: First, they replicated the familiar "morning" and "evening" personality types. According to their analysis, morning people are most alert from 9 a.m. to 11 a.m. Their level of sleepiness gradually rises throughout the day, and by evening, they express significantly higher levels of sleepiness than the other three chronotypes. Evening types, on the other hand, are considerably more tired than morning types when they wake up—but not as tired as afternoon types. Evening types don't really get going until about 10 in the morning. Their level of alertness, however, stays consistently high throughout the day; sleepiness does not set in until after 10 p.m.

For the two new types identified in this research, "afternoon" types wake up with the highest levels of sleepiness out of all the groups. Sleepiness abates by about 11 a.m., and their alertness stays high until approximately 5 p.m. At that point, sleepiness begins to set in again and rises steadily into the late evening. Interestingly, "nappers" are the only group that shows a double-peaked sleepiness curve across hours of the day. Similar to morning types, nappers begin the day very alert and remain that way until about 11 a.m. Then sleepiness starts to set in—peaking at around 3 p.m. After that, alertness returns until approximately 10 p.m., at which point sleepiness increases again, but less sharply than for the other groups.

Interestingly, the researchers examined the extent to which various demographic and lifestyle differences might shape a person's chronotype. What they found, however, is that these differences have less to do with one's chronotype than might be expected. Their analysis, they write, "illustrates that such four patterns were identical for subsamples of either daytime or shift/night workers, either males or females, and of either younger than 25 years or older age."

And while previous research has suggested there may be other chronotypes beyond just morning and evening types—for example, some have hypothesized the existence of a group that is hyper-alert throughout all hours of the day and another group that is generally more regardless of the time of day—the chronotypes discovered in this research are different from previous conceptualizations.

The authors conclude, "Evidence is gradually accumulating in favor of distinguishing at least four rather than two distinct chronotypes. [...] In post-industrial societies, the vast majority of the population might be classified into these four distinct chronotypes while only the minority of population might have intermediate (neither) chronotype."

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