Few large scale population studies have been done to accurately determine exactly what percentage of the general population has night owl, early bird or intermediate characteristics. Dr. Richard Coleman, a chronobiologist who has worked extensively in developing shift and night work schedules, maintains that only about 10 percent of the population are extreme owls or extreme larks/early birds. Most other sources state that intermediates account for 80% of the population and night owls and early birds account for the remaining 20%.
These numbers often reflect what could be referred to as “functional” night owls, early birds and intermediates. That is, because of social, cultural or lifestyle factors, we are often obliged to follow schedules not of our own choosing and may, therefore, appear to be, for example, intermediates when we are really “physiological” night owls or early birds.
A study which involved 48 university students in England included 18 (37%) moderate to definite Morning types, 20 (41%) moderate to definite Evening types and 10 (21%) Intermediate types. At the time of the study, these results were considered to be high for evening types because the sample consisted of young university students who tend to follow a night owl type of schedule, but nevertheless, the morning types make up a greater percentage of the group than the 20% generally believed to be representative of the population.
Jeffrey Larson, a family therapist at Brigham Young University in Utah, conducted a study with 150 couples. In this group of 300 people, 134 or 44% were morning types, 96 or 32% were evening types and 24% were undifferentiated.
As is readily apparent, these few studies have established little consistency in the percentages attributed to each type. Certainly, sample size and composition of the group in question is a factor. In addition, the studies were undertaken with objectives other than providing population information. The determination of types in the group was incidental to the testing of other hypotheses. To this extent, the known scientific studies did not sample a broad range of the general population.
It is also important that the same time definitions be used in categorizing night owls, early birds and intermediates. This has not always been the case and may be a reason for some of the inconsistencies in results.
In an effort to determine just what the percentages in the population might be, I surveyed a total of 419 people. Knowing that people were often obliged to follow work and social schedules not of their choosing, I made a point of having them distinguish between their daily schedule and their preferred schedule and used the time definitions established by Horne and Ostberg and used by them to distinguish morning, evening and intermediate types with the Morning-Eveningness Questionnaire.
The first 102 people were surveyed several years prior to writing the book. They were from three different groups, from a number of different urban and rural locations and represented all ages and diverse occupational and economic backgrounds. The majority of the people (317) were surveyed in the year prior to writing the text and represented five different groups from several cities. The groups were comprised of men and women of all ages, occupations and economic backgrounds. They represented various cultures, but were predominately white and middle class.
Overall, the daily schedules followed by most people differ markedly from the schedules they would prefer to follow if they weren’t encumbered by work and family responsibilities. This is most clearly indicated by the fact that on a daily basis fully 85% of the people follow an early bird schedule in the morning, but given any choice in the matter, only 22% would continue to do so. By far, the greatest majority of people would prefer to rise after 7:45 in the morning, but instead they are regularly rising before 6:30 and 7:00 in the morning.
At the opposite end of the scale, 21% of the people would prefer to rise at 10 or 11 o’clock in the morning, but only about 2% have this luxury on a daily basis. Interestingly, the people in the survey who followed this schedule on a daily basis had occupations in the arts or entertainment fields.
When it comes to retire to one’s bed, however, few people are truly early birds in their daily or preferred schedules. Only about 7% of the people choose to be in bed by 10 o’clock in the evening. There is little difference in the number of people who follow this schedule daily and those who prefer this schedule. True early birds simply cannot stay up later in the evening and they will fall asleep at their preferred time.
There are, however, a few people, and the key words are “a few” who are truly early birds and who find themselves staying up an hour or so later than they would prefer because of social, family and community obligations. They then find themselves sleeping an hour or so later in the morning and given the choice would choose both an earlier rising and retiring schedule than they follow on a daily basis.
At the opposite end of the scale, between 11.3 – 13% of the people find themselves going to bed at 12:30 a.m. or later on a daily basis, but given any choice in the matter, this number would swell to 31% of the people. One factor affecting this is our tendency to “phase delay” because of our circadian clock operating closer to 25 hours, but nevertheless, it would appear that many people are going to bed earlier than they would prefer, knowing that this is necessary if they are to be awake and able to get to work in the morning.
By far the largest group in this survey is the Intermediates, but this number is closer to 60% and not 80% as most sources suggest it should be. These intermediates most commonly prefer a schedule that would see them rising around 8 o’clock in the morning and going to bed sometimes around midnight. The next largest group is the Evening Types and the smallest group is the Morning Types.
Determining these types is complicated by the fact that people do not hold true to type for both the rising and retiring criteria. Only 1 – 6.75% of the people preferred an early bird type of retiring schedule, but fully 22% preferred an early bird type of rising schedule. On the other hand, 31% of the people preferred a night owl schedule for retiring in the evening, but only 21% would choose a night owl schedule for rising in the morning.
I would not presume to suggest that the results of my surveys are 100% accurate, but I think it is fair to suggest that night owls and early birds account for a greater share of the general population than most sources would suggest. They are not the anomaly some believe them to be. However, until scientifically-sound, large scale studies are done, we cannot make any more precise statements than that.