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Differences in the manner circadian clocks entrain to the 24-h day are expressions of different chronotypes that can range from extreme early to extreme late, from proverbial larks to owls. The Morningness Eveningness Questionnaire (MEQ) was one of the first to assess daily preference based on subjective self-assessment – a psychological construct. The later developed Munich Chronotype Questionnaire (MCTQ) uses instead the actual sleep timing to assess chronotype. It calculates the mid-sleep point, halfway between onset and offset on work-free days (MSF), which is then corrected for potential oversleep on free days compensating for sleep debt accumulated over the workweek (MSF sc ). MSF sc  is expressed in local time and is thought to be a proxy for “phase of entrainment” of the circadian clock. The MCTQ-derived chronotype is therefore a biological construct. In the present report, we validate the Portuguese variant (MCTQ PT ) of the MCTQ. Portugal is of particular interest, since it is thought to consist of especially late chronotypes.    Methods  We have used three methods to assess the timing of daily behavior, namely, the  chronotype  (MCTQ), the  daily preference  (rMEQ), and a  simple self-assessment  (time-of-day type). A total of 80 healthy adults living in Portugal, with age and sex distributed according to the Portuguese population, were recruited. We analyzed 4 weeks of continuous records of actimetry data to validate the MCTQ PT  and used the rMEQ to compare between a  biological chronotype  (sleep timing) and a  psychological chronotype  (daily preference). MCTQ variables were analyzed by descriptive statistics; correspondence between measurements was done by Spearman correlations or cross-tabulation; in a subset of 41 individuals, test–retest reliability was assessed.    Results  MCTQ-derived variables (MSF, MSW, MSF sc ) correlated highly with their counterparts calculated from actimetry (MSW: rho = 0.697; MSF: rho = 0.747; MSF sc : rho = 0.646; all  p  < 0.001). The MCTQ assessment of the chronotype showed good test–retest reliability (rho = 0.905;  p  < 0.001). The rMEQ score correlates with MSF sc  (rho = −0.695;  p  < 0.001), and the agreement for the self-assessment with the MSF sc  was fair ( kw  = 0.386;  p  < 0.001).    Conclusion  The Portuguese variant of the MCTQ revealed to be a reliable questionnaire to assess the chronotype for the Portuguese adult population, as previously reported for other countries.

Validation of the Portuguese Variant of the Munich Chronotype Questionnaire (MCTQPT)