What Chronotype Is, and What It Says About Your Personality

Some people open their eyes before any alarm goes off and are already thinking clearly by seven in the morning. Others, at that same hour, aren’t quite themselves yet. The difference between the two has a name in psychology: chronotype, and research has found it goes well beyond a simple schedule preference.

The clock you carry inside, whether you notice it or not

Deep in the brain, in a region called the suprachiasmatic nucleus, sits a cluster of neurons that works like a biological clock. This clock doesn’t track the exact hours on a wall clock; instead it generates a cycle of roughly 24 hours (hence the word circadian, from the Latin circa diem, “around a day”) that regulates when your body releases certain hormones, when your temperature rises and falls, and when you feel more or less mentally alert.

That internal clock doesn’t run identically in everyone. In some people it runs slightly ahead of the solar day; in others, slightly behind. That difference, sustained over time, is what researchers call a chronotype.

It’s tempting to think of chronotype as a binary choice: either you’re “a morning person” or you’re “a night person.” Research describes something more nuanced: a continuous spectrum with three reference zones.

• Morning type: the internal clock runs ahead. Waking up is easy, the mind clears quickly, and tiredness sets in early at night.
• Evening type: the internal clock runs behind. Mornings are a struggle, and peak performance arrives in the afternoon or at night.
• Intermediate type: no strong lean toward either extreme. It’s by far the largest group; population studies often put it around 60% of people.

The questionnaire that opened up the field, in 1976

Serious scientific interest in measuring these differences took off in the 1970s. In 1976, British psychologist James Horne and Swedish physiologist Olov Östberg published a self-assessment questionnaire designed to sort a person into one of five categories, from “definitely morning type” to “definitely evening type.” That work became the most cited instrument in the entire field of chronopsychology, the discipline that studies how our psychological processes vary throughout the day, and it came with a physiological data point behind it: people classified into each of the five groups showed significantly different morning body temperatures.

That original questionnaire hasn’t gone unrevised. Christopher Smith, Colleen Reilly, and Karen Midkiff found in 1989 that the correlation between some of its items was fairly weak, which pointed to the scale possibly measuring two related but distinct factors rather than one clean dimension, and proposed a revised version. Years later, Austrian researcher Aljoscha Neubauer found that the original cutoff points identified fewer morning types than expected when applied to a sample of Austrian students, and concluded that a questionnaire’s cutoff points probably need adjusting for the population they’re applied to.

A different approach came from German researcher Till Roenneberg with his Munich ChronoType Questionnaire: instead of asking about subjective preferences, it asks directly what time you fall asleep and wake up on workdays and on free days, and calculates the midpoint of sleep on free days. That figure correlates consistently with the classic Horne and Östberg classification, although each instrument captures a slightly different thing: the preference questionnaire is more influenced by social factors, while Roenneberg’s approach more directly reflects the internal biological clock.

Why this isn’t a matter of discipline

The most common misunderstanding about chronotype is treating it like a character trait: “morning people are disciplined, evening people are lazy and can’t get organized.” The scientific evidence points the other way. Chronotype has a real genetic component, and it also changes fairly predictably over the course of a life: adolescence pushes the biological clock toward eveningness, and from middle age onward, a good part of the population starts shifting back toward morningness.

What it says about your personality, according to research

Beyond the biology of sleep, a Spanish study went a step further and asked a different question: do morning and evening types actually have different personalities, beyond the stereotype? Researchers Juan Francisco Díaz Morales and Marta Aparicio García, of Universidad Complutense de Madrid, gave 189 people two instruments: a chronotype scale and the Millon Index of Personality Styles, a model that assesses motivational, cognitive, and interpersonal-behavior dimensions.

The study’s most consistent finding had nothing to do with sociability, as often assumed, but with cognitive style: the way a person takes in and transforms information from their environment.

• Morning-type people showed a significant preference for concrete information and direct experience, along with a tendency to absorb that information by relying on existing knowledge frameworks, a style the authors describe as more systematic and organized.
• Evening-type people showed the opposite tendency: a preference for symbolic, ambiguous information, and a stronger lean toward innovation, meaning fitting information into new, original frameworks rather than familiar ones.

Here comes the result that will probably surprise anyone who takes the extroverted, sociable night owl stereotype for granted: the study found no significant relationship between eveningness and extraversion, as measured by Hans Eysenck’s classic model. Earlier research had suggested that connection, but with inconsistent results, and this study didn’t confirm it clearly either. What it did find was a difference around social norms: morning-type people scored higher on conformity, meaning a stronger tendency to respect established customs and conventions, while evening-type people showed somewhat less conformity toward those same norms.

The group almost nobody talks about

Most chronotype research focuses on comparing the two extremes, leaving the intermediate group in the background, despite being, as noted above, the largest of the three. In this study’s sample, intermediate-chronotype people showed, for instance, greater indecisiveness in their social relationships than morning types, a nuance that disappears entirely if you only compare the two poles. This is exactly why researchers like Ana Adan, who specializes in chronopsychology, argue for treating the intermediate chronotype as a category in its own right, not as a simple midpoint between morning and evening types.

Work schedules shape chronotype too

The relationship between your life schedule and your chronotype probably runs in both directions. A study carried out by Neus Fernández and colleagues at Hospital de Jove in Gijón, analyzing 96 hospital workers, found that those with a work schedule that excluded night shifts scored significantly more toward morningness than those who did work nights, and that having spent more than ten years at the same company was also associated with a stronger lean toward morningness. Your biological clock shapes which schedule feels more comfortable to you, but sticking to a given schedule for years also appears to leave its own mark on how that clock expresses itself over time.

What to take away from all this

Neither the stereotype of the rigid early riser nor the one of the disorganized night owl holds up well against the data. What the research describes is something more modest, and at the same time more interesting: two distinct cognitive styles, neither superior to the other, each with its own advantages depending on the task, and a third group, the intermediate type, that rarely comes up in conversation despite often being the largest of the three. Underneath it all sits a real biological clock you didn’t choose, one that rarely lines up perfectly with the schedule the world around you demands.

Sources

• Horne, J. A., & Östberg, O. (1976). A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. International Journal of Chronobiology, 4, 97-110.
• Smith, C. S., Reilly, C., & Midkiff, K. (1989). Evaluation of three circadian rhythm questionnaires with suggestions for an improved measure of morningness. Journal of Applied Psychology, 74(5), 728-738.
• Neubauer, A. C. (1992). Psychometric comparison of two circadian rhythm questionnaires and their relationship with personality. Personality and Individual Differences, 13(2), 125-131.
• Roenneberg, T., Wirz-Justice, A., & Merrow, M. (2003). Life between clocks: daily temporal patterns of human chronotypes. Journal of Biological Rhythms, 18(1), 80-90.
• Díaz Morales, J. F., & Aparicio García, M. (2003). Relaciones entre matutinidad-vespertinidad y estilos de personalidad. Anales de Psicología, 19(2), 247-256.
• Fernández, N., Hinojal, R., Díaz, J., Sáiz, P. A., González, M. P., & Bobes, J. (2003). Valoración de tipología circadiana en trabajadores de un hospital general. Archivos de Prevención de Riesgos Laborales, 6(1), 77-83.