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Table 1 Sleep habits by bedtime

From: Association between delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan

  Whole Up to 2100hG 2100hG 2130hG 2200h or later G F / χ 2 p
Number of participants 425 121 137 77 90   
Bedtime (BT) (h) 21.2 ± 0.9 20.2 ± 0.5 21.0 ± 0.1 21.5 ± 0.1 22.4 ± 0.6 649.293 <0.001
Sleep onset latency (SOL) (min) 29.9 ± 15.7 29.3 ± 14.4 30.7 ± 16.6 30.1 ± 14.7 29.1 ± 16.7 0.266 0.850
Sleep onset time (SOT) (h) 21.7 ± 0.9 20.7 ± 0.5 21.5 ± 0.3 22.0 ± 0.2 22.9 ± 0.6 461.334 <0.001
Wake time (WT) (h) 7.2 ± 0.9 6.7 ± 0.6 7.0 ± 0.8 7.4 ± 0.6 7.9 ± 1.0 50.859 <0.001
Time in bed (TIB) (h) 10.0 ± 0.8 10.5 ± 0.7 10.0 ± 0.8 9.8 ± 0.6 9.5 ± 1.0 26.125 <0.001
Total night sleep time (TST) (h) 9.4 ± 0.9 9.9 ± 0.7 9.4 ± 1.0 9.2 ± 0.8 8.9 ± 1.0 22.193 <0.001
Wake after sleep onset (WASO) (min) 6.6 ± 21.4 5.3 ± 17.3 7.0 ± 27.1 7.7 ± 18.1 7.0 ± 19.6 0.247 0.864
Sleep efficiency (SE) (%) 93.9 ± 4.6 94.5 ± 3.3 93.7 ± 5.5 93.6 ± 4.4 93.7 ± 4.6 1.040 0.375
Total daytime sleep time (NAP) (min) 1.8 ± 0.7 1.6 ± 0.5 1.8 ± 0.8 1.9 ± 0.6 2.1 ± 0.6 7.078 <0.001
Bedtime irregularity (%) 41.9% 33.1% 38.7% 49.4% 52.2% 10.163 0.017