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Table 1 The demographic characteristics and comparison of a low-IHS and high-IHS group following a median split, on PIU, sleep, internet usage time, twitter usage, and school performance

From: Survey of the effects of internet usage on the happiness of Japanese university students

  Overall (N = 1258) Low-IHS (N = 595) High-IHS (N = 663) t-value P value*
Mean SD Mean SD Mean SD
Total N (%) 1258 (100%) 595 (47.3%) 663 (52.7%)   
Sex (%)
 Male 544 (100%) 289 (53.1%) 255 (46.9%) χ2 value 3.963 Male vs Female < 0.001
 Female 714 (100%) 306 (42.9%) 408 (57.1%)
Age 19.34 1.10 19.44 1.13 19.26 1.08 2.900 0.004
Happiness (IHS) 30.60 6.53 25.12 4.47 35.52 3.44 −45.893 < 0.001
IAT 37.87 12.59 40.62 13.43 35.40 11.24 7.438 < 0.001
PSQI global score 5.88 2.52 6.48 2.54 5.33 2.38 8.269 < 0.001
Subjective sleep quality 1.13 0.71 1.26 0.71 1.02 0.69 6.154 < 0.001
Sleep latency 0.99 0.92 1.15 0.96 0.84 0.85 6.165 < 0.001
Sleep duration 1.69 0.98 1.74 0.97 1.66 0.99 1.477 0.140
Habitual sleep efficiency 0.21 0.56 0.25 0.61 0.17 0.50 2.415 0.016
Sleep disturbance 0.68 0.50 0.75 0.49 0.62 0.51 4.914 < 0.001
Use of sleeping medications 0.04 0.32 0.05 0.33 0.03 0.30 0.874 0.382
Daytime dysfunction 1.13 0.71 1.28 0.87 1.00 0.89 5.529 < 0.001
Internet usage time/ min (Weekday) 205.79 147.70 215.69 159.08 196.95 136.25 2.224 0.026
Internet usage time/ min (Weekend) 277.63 183.86 296.74 197.60 260.63 169.04 3.434 < 0.001
Number of Twitter follows 218.18 393.53 215.35 456.81 220.70 327.14 −0.239 0.811
Number of Twitter followers 256.73 1354.17 280.50 1859.24 235.53 623.13 0.584 0.559
Number of times skipping a whole day of school 1.26 .551 1.33 0.64 1.19 0.45 4.206 < 0.001
Number of times arriving late for school 1.33 .655 1.41 0.76 1.25 0.54 4.295 < 0.001
  1. SD standard deviation, IHS Interdependent Happiness Scale, IAT The Internet addiction test, PSQI The Pittsburgh Sleep Quality Index
  2. *Bold text indicates a statistically significant difference after Bonferroni correction