Chronotype: a review of the advances, limits and applicability of the main instruments used in the literature to assess human phenotype.

The study of circadian typology differences has increased in the last few years. As a result, new instruments have been developed to estimate the individual circadian phase of temporal human behavior, also referred as chronotype. The current review was conducted to evaluate the differences among the questionnaires most frequently used to assess chronotype: the Morningness-Eveningness Questionnaire (MEQ), the Composite Scale of Morningness (CSM), and the Munich Chronotype Questionnaire (MCTQ). Each instrument evaluates a different aspect of chronotype. MEQ is considered to evaluate the phase preferences of individual behavior over a 24-hour day, while MCTQ measures the phase of sleep positions for both free and work days. CSM is similar to MEQ, but is more sensitive to measure shift work. The concept of chronotype has been used to refer to phase positions or phase preferences in the literature reviewed. Most of the time this is a consequence of different interpretations: it is not clear whether phase preferences are a direct manifestation of the individual's internal clock or a result of external cues, e.g., social interaction (including the alarm clock). Also, phase preferences are not uniform throughout life. Therefore, a single assessment, not taking age into consideration, will not accurately describe the sample. We suggest that MCTQ is the best instrument for investigators dealing with desynchronization and as an instrument for sleep phase. Conversely, if the goal is to assess characteristics that change under specific situations - chronotype -, the MEQ should be used.