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Table 3 Sociodemographic and sleep characteristics and lifestyle in the groups with sleep problems

From: Impact of sleep problems on daytime function in school life: a cross-sectional study involving Japanese university students

  Insomnia
(n = 257)
Without Insomnia
(n = 754)
BIISS
(n = 28)
Without BIISS
(n = 916)
DSWP
(n = 20)
Without DSWP
(n = 936)
BIISS + DSWP
(n = 46)
Without BIISS + DSWP
(n = 898)
Age (y) 19.8 ± 1.2 19.6 ± 1.2 a 20.0 ± 1.2 19.7 ± 1.2 19.8 ± 1.0 19.7 ± 1.2 19.9 ± 1.0 19.7 ± 1.2
Sex
 Female (%) 79 78 100 79 a 70 80 87 79
Grade
 Freshman (%) 31 37 25 36 25 36 20 36
 Sophomore (%) 24 23 25 23 15 23 28 22
 Junior (%) 30 27 32 27 50 27 37 27
 Senior (%) 16 14 18 15 10 15 15 15
Living alone
 Yes (%) 21 21 0 22 a 55 20 a 17 21
Commute time (min) 59.6 ± 33.4 59.5 ± 34.4 85.4 ± 25.1 58.5 ± 33.5 a 23.2 ± 20.0 60.0 ± 33.3 a 66.2 ± 34.2 58.9 ± 33.5
School hours (h) 6.9 ± 1.9 7.0 ± 1.8 7.4 ± 1.4 7.0 ± 1.8 6.1 ± 1.6 7.0 ± 1.8 a 6.8 ± 2.0 7.0 ± 1.8
Class start time (h:m) 9:18 ± 0:46 9:20 ± 0:46 8:59 ± 0:26 9:18 ± 0:45 a 10:04 ± 1:11 9:17 ± 0:44 a 9:22 ± 0:51 9:18 ± 1:36
Class closing time (h:m) 16:11 ± 1:39 16:17 ± 1:35 16:22 ± 1:22 16:15 ± 1:37 16:07 ± 1:57 16:15 ± 1:36 16:10 ± 1:39 16:16 ± 1:37
Club activities
 Yes (%) 32 41 a 14 39 a 45 38 22 39 a
Part-time job
 Yes (%) 65 68 68 66 75 66 78 65
Exercise habit
 Yes (%) 46 49 25 49 a 50 47 33 49 a
Alcohol consumption
 Yes (%) 47 41 57 42 55 42 59 42 a
Smoking
 Yes (%) 6 5 4 5 20 5 a 4 5
Self-rated health status
 Poor (%) 41 22 a 25 27 20 27 39 26
Stress
 Yes (%) 56 41 a 46 45 45 45 65 44 a
Duration of nap
  < 10 min (%) 27 31 31 30 20 30 15 31
 10–29 min (%) 30 36 35 34 45 34 37 34
 30–59 min (%) 22 19 19 19 10 20 24 19
 ≥ 1 h (%) 21 13 b 15 15 25 15 24 15
Frequency of dreaming during nap
 Often (%) 18 12 b 11 14 10 14 26 13 b
 Sometimes (%) 53 53 64 52 60 52 52 53
 Not (%) 30 35 25 33 30 33 22 34
Sleep-related symptoms
 Difficulty initiating sleep (%) 76 10 a 25 26 30 26 39 26 a
 Difficulty maintaining sleep (%) 24 5 a 7 10 5 10 13 9
 Early morning awakening (%) 15 4 a 4 6 0 6 4 6
 Difficulty awakening (%) 42 51 a 43 49 80 49 a 74 48 a
 Hypnagogic hallucination (%) 27 15 a 32 18 15 19 35 18 a
 Sleep paralysis (%) 15 10 a 11 12 15 11 20 11
 REM parasomnia [7] (%) 57 47 a 57 49 60 49 61 49
 NREM parasomnia [8] (%) 24 15 a 14 17 35 16 a 24 16
  1. asignificantly difference between the students with the sleep problem and without the sleep problem
  2. bsignificantly higher than other students by residual analysis (adjusted residual ≥1.96)
  3. BIISS Behaviorally induced insufficient sleep syndrome, DSWP Delayed sleep-wake phase
  4. REM Rapid eye movement, NREM Non-rapid eye movement
  5. REM parasomnia: nightmare and / or acting out their dreams
  6. NREM parasomnia: night terrors, defective awakening, and / or sleep walking