Chronotype and Social Jet Lag Assessment

Chronotype was measured using the Korean version [45 (link)] of the Morningness-Eveningness Questionnaire (MEQ-K) [46 ]. The MEQ-K comprises 19 items, with a total scoring range of 16–86 points (11 items [scoring range 1–4 points]; 2 items [scored 0, 2, 4, and 6]; 1 item [scored 0, 2, 3, and 5]; 5 items [scoring range 1–5 points); a higher score indicates a more extreme morning type [46 ]. Based on the criteria of total scores, chronotype was categorized into three groups: morning chronotype (59–86), neither chronotype (42–58), and evening chronotype (16–41) [47 (link)]. The reliability (Cronbach’s α) of the MEQ was 0.82 at the time of development [46 ], 0.77 for MEQ-K [45 (link)], and 0.64 in this study.
The SJL was measured using the Munich Chronotype Questionnaire (MCTQ) [48 (link)]. The MCTQ comprises 14 items about bedtime, sleep onset, sleep latency, time of awakening, time to get up, use of an alarm, and outdoor activity time, to assess weekday and weekend sleep-wake cycles. Cheng and Hang [49 (link)] established the reliability of the MCTQ by confirming that the sleep-wake patterns measured using the scale are closely linked to actigraphy results. SJL was calculated based on the sleep-corrected SJL formula by Jankowski [50 (link)].
Daily light exposure was calculated based on the response on the MCTQ about the time spent outdoors without a roof during the daytime on weekdays and holidays. Sleep duration was calculated as the time from sleep onset to time of awakening based on the response on the MCTQ.