Regarding the internal consistency of the

Regarding the internal consistency of the total scale, estimated through the Cronbach׳s alpha, the obtained results suggest minimal adequacy of the scale according to Nunnaly׳s criteria [26]. We also attempted to study the discriminant capacity of the QSAR in discriminating OSAS subjects from healthy individuals. To accomplish this goal, a ROC analysis was conducted on the total score of the scale. The data indicated a good discriminant performance of the scale. The cut-off score was also estimated under the same statistical procedure. The best cut-off point with adequate level of sensitivity and specificity in discriminating subjects with OSAS is of 10.5. The probability of discrimination a true positive (OSAS; i.e., sensitivity) was, in average, 87%, whereas the probability of discrimination a true negative (without OSAS; i.e., specificity) was, in average, 80%. More particularly, a total score in the QSAR of 10.5 or more may be indicative of OSAS. The obtained data for sensitivity and specificity are encouraging when compared with the most commonly used screening methods for OSAS [16]. The RMT suggests that the standard version of the QSAR is consistent with the theory guidelines [22], scores show good model fit and psychometric adequacy. The main indicators reveal an adequate adjustment between persons and measure.
Conflicts of interest
Authorship contribution
Introduction Chronobiology organization constitutes itself as one of the parameters responsible for inter-individuality differences. Three human chronotypes are described: morning (“larks”), evening (“owls”) and indifferent. They are characterized by individual preferences for activity realization during a determined fgf receptor inhibitor of the day, with better alertness during morning, evening or without any preference, respectively [1]. Regardless of the individual chronotype, synchronization and regularity of the sleep–wake cycle, is a must. In medical students, this process is modified by various factors, such as curricular load during the entire day, extra-curricular activities, physical and emotional stress, pressure for high academic performance and influence of hospital demands [2,3]. Learning process and humor status are also conditioned by sleep–wake cycle and influenced by the quality and duration of sleep [4]. When compared to normal population, medical students show an average of 6h of sleep per day, a result that is inferior to the 8h per day, commonly found in the normal population [2,5]. It is supposed that individual circadian preferences for sleep–wake cycles are, till a certain degree, under genetic and hereditary control [6–10]. Possibly, such association derives from intrinsic properties of the circadian system [11], and it is also believed that diurnal preference as well as the quality of sleep, demonstrate a strong genetic component. A series of studies were conducted to verify the relationship between genes and variables of the circadian rhythm [12]. Environmental influence, on other hand, did show a low correlation with these phenotypes [11].
Methods
Results The mean score value to classify the chronotype was of 50.9±11.1. Categorically, 46 students (20.8%) were classified as evening type, 114 (51.6%) as indifferent and 61 (27.6%) as morning types. Table 1 demonstrates that the comparison of the values of the PSQI between the chronotype groups was statistically significant (p<0.0005), with the lowest values for the students with morning chronotype and the highest values for the evening chronotype individuals (Fig. 1). The variables age and diurnal sleepiness were not significant when comparing the chronotype groups. We have observed a significant negative correlation between the scores of the chronotype questionnaire (MEQ) and the quality of sleep (PSQI) (rho=−0.3; p<0.0005) (Fig. 2). The negative correlation suggests that the eveningness – low scores for MEQ – were associated with poor quality of sleep – high scores for PQSI. We have not observed a significant correlation between the scores for MEQ (chronotype) and the ones for ESS (diurnal sleepiness). We did not observe any difference between the evening, indifferent and morning groups in terms of gender and season at birth (Table 2).