Edited by: Achim Kramer, Charité – Universitätsmedizin Berlin, Germany
Reviewed by: Hanspeter Herzel, Humboldt University of Berlin, Germany; Eran Tauber, University of Haifa, Israel
†These authors have contributed equally to this work
This article was submitted to Chronobiology, a section of the journal Frontiers in Physiology
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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 (MSFsc). MSFsc 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 (MCTQPT) of the MCTQ. Portugal is of particular interest, since it is thought to consist of especially late chronotypes.
We have used three methods to assess the timing of daily behavior, namely, the
MCTQ-derived variables (MSF, MSW, MSFsc) correlated highly with their counterparts calculated from actimetry (MSW: rho = 0.697; MSF: rho = 0.747; MSFsc: rho = 0.646; all
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.
The 24 h light–dark cycle is a fundamental characteristic of the planet Earth, and as so, it influences the behavior, metabolism, and physiology of species from all phyla, from unicellular organisms (
The individual daily behavior can be considered a personality trait, where individual preference is assessed by ordinal values. This is the approach used in the Morningness–Eveningness Questionnaire (MEQ), the first validated instrument for chronotyping (
However, a chronotype has a genetic basis and is influenced by not only age and gender (
The Munich ChronoType Questionnaire (MCTQ) was developed as a practical proxy for circadian “phase of entrainment” (
The MCTQ has been applied in many different countries: Japan (
Here, we introduce and validate the European Portuguese variant (MCTQPT) of the MCTQ. We used actimetry to validate the MCTQ and the rMEQ to compare between a
The original English variant of the questionnaire was translated by two individuals proficient in both English and Portuguese. A consensus version was obtained between the translators and the investigators, which was subsequently back-translated to English by a third translator of equal qualification, essentially producing the same questions as the original (back-translation was approved by the original developers of the MCTQ). We tested comprehensibility, semantic validity, and cultural adequacy of the Portuguese MCTQ variant (MCTQPT) in a preliminary survey, which did not lead to additional text changes. Data were assessed in the context of other experiments. On average, participants took 7 min to complete the MCTQPT.
Our study included sociodemographic questions (age and gender), the MCTQPT, the rMEQ, wrist actimetry (24 h/day for 4 consecutive weeks), and keeping a sleep-log during the 4-week period. In this paper, we apply three methods of assessing the timing of daily behavior:
For validation purposes, we compared the MCTQPT results of 80 healthy individuals to the objective sleep–wake assessment of actimetry. Test–retest reliability of the MCTQPT was also assessed in a subset of 41 participants.
A sample of 80 Portuguese-speaking volunteers (age ≥18 and ≤65) living in Portugal was recruited between March 2017 and March 2018. Since the MCTQ needs sleep information for both work- and work-free days, we focused on working adults. Sex and age distribution mirrored the national Portuguese distribution (
All participants gave their written informed consent, and the Lisbon Medical School Ethics Committee approved the study design.
The MCTQ queries sleep times, and its chronotype is considered a quantifiable circadian trait based on MSFsc (see the Introduction). Note that a chronotype is expressed in local time and can only be calculated if participants report not using alarm clocks on work-free days. Since MSFsc is a continuous variable, a quantile approach was used (
The rMEQ is a short version of the MEQ (
Note that the two instruments have an inverse relationship: an individual with a morning preference leading to a high rMEQ score (i.e., >18) has an early (“low”) mid-sleep time on free days in the MCTQ (i.e., an MSFsc at 2:30).
The time-of-day-type term was already used for a seven-category self-assessment of the chronotype (
Locomotor activity was recorded for 4 weeks with wrist-worn devices (Condor InstrumentsTM). Participants could follow their usual routines, in their home and work environment. Activity was sampled every second and stored in 1-min bins; for data analyses in the ChronoSapiens software (vs 11.x; © Chronsulting UG), data were binned further in 10-min bins. Times of not wearing the actimeter were defined as stretches of at least 10 consecutive bins (100 min) without activity. These “missing data” were excluded from the analysis. We also excluded entire days including ≥4 h of missing data. The shortest time series after data cleaning was 11 days, which contained at least 2 weekends (4 work-free days); 76 participants (97.5%) completed the 4 weeks of actimetry. Information about work- and free days was retrieved from the sleep logs. The actimetry from two individuals had to be discarded for technical reasons. Phase assessments of the activity recordings and derived sleep variables (sleep onset, sleep end, mid-sleep, and sleep duration) were calculated with published algorithms (
The MCTQ variables were analyzed using descriptive statistics [mean ± standard deviation (SD) or median with interquartile range (IQR)]. Normality of MCTQ variables, rMEQ scores, and actimetry data was analyzed by the Shapiro-Wilk test. The MCTQ variable comparisons for work- and work-free days were assessed with the paired samples
The concordance between the MCTQ and actimetry, the test–retest of the MCTQ, as well as the association between the MCTQ with the rMEQ and age were assessed by Pearson (r) or Spearman (rho) correlations.
In order to assess the discrepancies between actimetry and MCTQ variables, the difference (Δ) for the mid-point of sleep, sleep onset (SO), and sleep end (SE) for work- and work-free days was calculated. The sum of squared differences (SSD) was calculated for the respective differences (Δ). A higher SSD represents a higher discrepancy between actimetry and the MCTQ. Time-of-day-type self-assessment and MSFsc were compared by a cross-tabulation using the respective quartiles of the MSFsc distribution and the four self-report categories. Weighted kappa (kw; linear weights for two ordinal variables;
We used the MCTQPT to assess the sleep–wake behavior on both workdays and free days (
Timing of sleep–wake behavior on workdays (red) and work-free days (green) derived from the MCTQ. The bottom brighter green box represents MSFsc. Sample size
The chronotype (MSFsc) was not normally distributed [median (IQR): 4.55 (1.53)
Distribution of chronotype (MSFsc; sleep-corrected mid-sleep on free days; local time). Sample size = 62, average age 40.45 ± 14.89 years, ranging from 18 to 65 years.
Concordance rate between self-assessment categories and MSFsc quartiles distribution in local time (24 h scale).
MSFsc quartiles distribution | ||||||
Self-assessment | N | 2.07–3.72 | 3.73–4.55 | 4.56–5.26 | 5.27–8.75 | Concordance rate (%) |
“Definitely a morning-type” | 5 | 5 | 0 | 0 | 0 | 100 |
“Rather more a morning-type than an evening-type” | 36 | 9 | 13 | 10 | 4 | 36 |
“Rather more an evening-type than a morning-type” | 18 | 1 | 3 | 6 | 8 | 33 |
“Definitely an evening-type” | 3 | 0 | 0 | 0 | 3 | 100 |
Social jetlag (SJL), a measure of circadian misalignment given by the difference between the mid-point of sleep on free days and workdays (SJL = MSF – MSW), was not normally distributed [median (IQR): 0.90 (1.10)].
The distribution of the mid-sleep point on workdays was also not normal [MSW: median (IQR): 3.82 (1.28)], while the mid-sleep point on free days (MSF) was normally distributed (mean: 4.92 ± 1.37).
A subset of 41 participants (16 men; average age of 44.12 ± 14.54 years, range: 18–64) was selected due to their stable lifestyle between subsequent collections (e.g., no travels or changes in work schedule, no vacations, DST change). These participants were asked to complete the MCTQPT a second time, 2–6 weeks after the initial completion. The MCTQ variables correlated highly between baseline and follow-up [MSF (41) rho = 0.834, MSW (41) rho = 0.831, MSFsc (30) rho = 0.905; all
MCTQ-derived variables were measured by actimetry. Actimetry-derived MSW times were normally distributed (mean: 4.20 ± 1.07) as were those of MSF (mean: 5.10 ± 1.32) and SJL (mean: 0.93 ± 0.91). The distribution of actimetry-derived MSFsc times were, however, skewed [median (IQR): 4.59 (1.53)]. The corresponding variables from the MCTQ and actimetry (MSW, MSF, MSFsc, and SJL) correlated highly (MSW: rho = 0.697; MSF: rho = 0.747; MSFsc: rho = 0.646; SJL: rho = 0.452; all
The respective SSD (sum of square differences) between the questionnaire and actimetry for sleep onset (SO), mid-sleep point (MS), and sleep end times (SE) for work- (w) and work-free days (f) were: ΔSOw = 71.67; ΔMSW = 61.53; ΔSEw = 59.62; ΔSOf = 77.86; ΔMSF = 58.04; ΔSEf = 89.76.
The phase of minimal activity (φmin) was normally distributed both on work- (mean: 3.73 ± 1.03) and free days (mean: 4.71 ± 1.30). Both workday and free day φmin advanced with age (
Spearman’s rho correlations for:
The distribution of the rMEQ scores was skewed [median (IQR): 14.0 (4.0)]. rMEQ scores correlated positively with age (rho = 0.311;
Spearman’s rho correlations between the rMEQ score and MCTQ variables:
The original reduced Morningness–Eveningness cutoffs were calculated using a Spanish population (
The rMEQ distribution score ranging from 4 to 25 (scores are plotted analogous to
According to the self-assessment of the time-of-day type, the majority consider themselves as “rather more a morning-type than an evening-type” (43, 53.8%), followed by “rather more an evening-type than a morning-type” (26, 32.5%), followed by “definitely a morning-type” (8, 10%) and “definitely an evening-type” (3, 3.8%). The agreement for the four categories of self-assessment with the MCTQ-MSFsc quartiles distribution had a fair agreement for the two measures (kw = 0.386, 95% CI: 0.239–0.533;
Our results show that the MCTQPT is a valid instrument to assess the chronotype (phase of entrainment) in the population of Portugal and that this subjective assessment corresponds well with objective actimetry.
The phase of minimal activity on free days (φmin of one-harmonic cosine fit) is highly correlated with the MCTQ-derived MSF. The corresponding workday correlation was slightly lower but also highly significant. Comparisons between MCTQ results and general daily activity profiles are assumption-free, e.g., no secondary sleep detection is required. However, specific activities (e.g., biking to work or jogging) affect the timing of the cosine fit.
To make more direct comparisons, we assessed objective sleep times within the activity recordings (
We did not validate against dim-light melatonin onset (DLMO), the gold standard for the circadian phase; however, in a recent validation study (
Strong correlations between actimetry data and MCTQ variables have been previously shown, for example, for MSF (
The MCTQPT showed high test–retest reliability similar to and with values within the same range as reported for German and Korean populations (
In our study, the weekly average sleep duration was of 7 h and 53 min (no reports < 5 h), which is in line with a 7- to 9-h recommendation for the considered age group (
A chronotype advances with age (
Men are generally later than women (
Earlier reports suggested that the Portuguese population is especially late (
According to these results, Koreans and Italians are – on average – later chronotypes than Portuguese. However, the ages of the participants in the respective studies bias the average chronotype of Koreans and Italians toward later chronotypes (
Country comparison of different studies representing the MCTQ average chronotype.
Country | MSFsc | Average age | References |
Korea | 5.13 ± 1.54 | 27.09 ± 5.64 | |
Italy | 4.75 ± 1.22 | 31.30 ± 13.00 | |
Portugal | 4.63 ± 1.39 | 40.40 ± 14.89 | Present study |
Germany | 4.40 ± 1.44 | 33.91 ± 12.96 | MCTQ database |
Japan | 4.31 ± 0.07 | 35.69 ± 11.92 |
Our participants were mainly from urban areas. This precludes direct comparison of our study with a recent Brazilian Portuguese-speaking study using the MCTQ, since that was developed within rural communities with different levels of urbanization (i.e., access to electrical light) (
Although the MCTQ and the rMEQ evaluate different traits of a chronotype, the results for these instruments correlated well, according to what has been shown before (
We also compared the MSFsc with the individual’s self-assessment of time-of-day type (
Our Portuguese sample has a later daily preference in comparison to the established cutoff values for the rMEQ (
The Portuguese variant of the MCTQ correlates well with actimetry and has high reliability. If we consider that there are around 290 million Portuguese language speakers around the world, the MCTQPT is an important instrument and an excellent chronotype assessment method – simple, short, and non-invasive. It is particularly useful to assess the chronotype among different countries, since it allows enhancing the knowledge of human phase of entrainment in real-life settings. In addition, the chronotype impacts both sleep quality (
The datasets presented in this article are not readily available because they are still part of an ongoing study. Requests to access the datasets should be directed to the corresponding author.
The studies involving human participants were reviewed and approved by the Lisbon Medical School Ethics Committee. The patients/participants provided their written informed consent to participate in this study.
CR, SM, LL, TP, and TR contributed to the design and implementation of the study. CR and SM collected the data, performed the statistical analysis, and wrote the manuscript. CR treated the actimetry data. TR supervised the study. All authors contributed to the article and approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We would like to thank translators Maria João Pereira, Ana Stilwell, and Joana Castro; Luísa Klaus Pilz for help with statistics; and Condor instruments for providing actimeters.
The Supplementary Material for this article can be found online at: