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Individuals differ in morningness-eveningness, which is their preferred time for intellectual and physical activities. Although it is a basic human trait, cross-cultural comparisons are scarce but interesting because they help to determine the influence of exogenous factors, such as ambient temperature, climate and photoperiod. We here compare a large sample of German and Turkish adolescents (N = 26 465) by using the Composite Scale of Morningness and the Morning Affect Factor. First, we show that the Morning Affect Factor and Morningness scores are equivalent in both countries and we report country differences with Turkish adolescents scoring higher on morningness (F1,26 038 = 1293.313, p < 0.001) and in the morning affect (F1,26 038 = 133.833, p < 0.001). This fits into the environment hypothesis suggesting that populations near the equator should be more morning oriented. Meanwhile, gender differences were small and adolescents showed a lower morningness and a lower morning affect with increasing age.

Sleep is a physiological need that affects physical and mental performances. However, the number of individuals who experience problems directly or indirectly related to sleep is increasing in various countries. Therefore, it is important to have a short, reliable and valid measure to assess both sleep quality and sleep related variables in school-age children. This study aims to carry out the validity and reliability studies for the Sleep Quality Scale and Sleep Variables Questionnaire (SQS-SVQ) used to determine sleep quality, parental control, total sleep time, mid-point of sleep and sleep efficiency and to adapt it into Turkish. The SQS-SVQ consists of seven scale items to measure sleep quality and eight questionnaire items. The validity and reliability studies of the instrument were carried out on data acquired from 4th-8th graders. Factorial validity for SQS and criterion related validity analyses were carried out for the validity of the SQS-SVQ and correlations ranged from 0.51 to 0.73. These analysis results put forth that the scale is a valid measurement tool. Internal consistency coefficient of the SQS was 0.72 and test-retest correlations of the SQS-SVQ ranged from 0.67 to 0.88. These acquired results indicated that the scale WAS reliable. Meanwhile, gender measurement invariance was tested for SQS and results indicated that gender measurement invariance was established. These results have shown that the SQS-SVQ can be used in social researches and especially in educational studies.

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