Косова, А. Л. Chronotype, sleep length, and school achievement of 11- to 23-year-old students in northern European Russia / Borisenkov M. F., Perminova E. V., Kosova A. L. // Chronobiol. Int. - 2010. - Vol. 27. - P. 1259-1270.

Chronobiol Int Downloaded from informahealthcare.com by 217.66.146.98 on 07/23/10 For personal use only. Students’ Chronotype and Sleep Length in the North 1263 college students. Questionnaires were distributed to the students by their teachers, and the children filled out the questionnaires in a classroom without assistance. In each of four settlements, the survey was carried out in two or three schools. In Syktyvkar, the survey was also carried out among students at three schools of two colleges, and in Apatity among students of two schools of one college. Incomplete questionnaires or ques­ tionnaires with mistakes were excluded from analysis (48 questionnaires). Ethical Measures This study was approved by the ethical committee of the Institute of Physiology of Komi Science Centre, Ural Branch of RAS, and was con­ ducted in accordance with the ethical and methodological standards established by the Journal for human biological rhythm research (Portaluppi et al., 2008). Measurement Instruments The Munich chronotype questionnaire (MCTQ) was used to assess chronotype and sleep length (Roenneberg et al., 2003). The question­ naire, which was translated from English into Russian, consists of simple questions concerning bedtime, time of awakening, and other behaviors. Chronotype and sleep length were calculated as described by Roenneberg et al. (2004). Chronotype was calculated as the midpoint of the sleep phase on weekends adjusted with the sleep debt accumulated on week­ days (MSFsc) expressed in hours. Sleep length was calculated as follows: Sleep length —([sleep length week days] x 6 + [sleep length weekends])/7 with the value expressed in hours. The dependence of chronotype and sleep length on place of residence was studied using the data of school chil­ dren living in settlements 1 through 4 and the college students living in settlements 2 and 4 (see Figure 1). All participants were also required to answer the question: “What mean score have you received for the last quarter (examinations)?” This question was analyzed to assess the depen­ dence of school achievement on chronotype and sleep length. In total, 926 school children and college students answered the question about their achievements. The Russian grading system is coded into five grade's. A low grade indicates low achievement. For the analysis, we used the following factors: age (11-23 уis); sex (M/F); place of residence (1-4), which was further divided according to latitude (south/north = 1,2/3,4), longitude (east/west = 1-3/4), and type of settlement (village/city = 1/2-4); and school achievements (0 = data absent; low score = 3-3.5; mean scores = 3.6-4.5; high scores = 4.6-5). R I Q Н Т В L 1 (SI К ф