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Table 4 Descriptive statistics of the total sample, test of gender differences, bivariate correlations between individual ISI items, and item-total correlations among male and female young adults

From: Validation of the German version of the insomnia severity index in adolescents, young adults and adult workers: results from three cross-sectional studies

  M SD Range Skew Kurt Gender differences
ANOVA Chi2-test
Descriptive statistics       F η2 Chi2 ϕ
Item 1 0.67 0.93 0-4 1.45 1.76 5.67* .007 --- ---
Item 2 0.66 0.92 0-4 1.47 1.80 9.46** .011 --- ---
Item 3 0.49 0.86 0-4 1.90 3.13 0.95 .001 --- ---
Item 4 1.09 1.04 0-4 0.82 0.03 2.61 .003 --- ---
Item 5 1.71 1.01 0-4 0.28 −0.57 1.63 .002 --- ---
Item 6 1.38 1.01 0-4 0.34 −0.56 1.79 .002 --- ---
Item 7 0.57 0.91 0-4 1.57 1.64 1.48 .002 --- ---
ISI total score 6.56 4.31 0-26 1.09 1.35 6.88** .008 4.67 .073
Bivariate correlations Item 1 Item 2 Item 3 Item 4 Item 5 Item 6 Item 7 rit
Item 1 --- .40*** .20** .63*** .19** .05 .58*** .53***
Item 2 .39*** --- .42*** .59*** .16* .11 .47*** .55***
Item 3 .30*** .48*** --- .36*** .10 .10 .29*** .36***
Item 4 .67*** .51*** .41*** --- .22** .10 .70*** .68***
Item 5 .28*** .20*** .17*** .26*** --- .52*** .29*** .37***
Item 6 .06 .07 .06 .09* .47*** --- .15* .25***
Item 7 .56*** .47*** .32*** .64*** .42*** .25*** --- .66***
rit .57*** .52*** .42*** .65*** .45*** .25*** .69*** ---
  1. Correlations for male participants are listed below the diagonal, correlations for girls above the diagonal. Item 1 = Difficulty falling asleep; Item 2 = Difficulty staying asleep; Item 3 = Waking up too early; Item 4 = How satisfied are you with your current sleep pattern?; Item 5 = To what extent do you consider your sleep problem to interfere with your daily functioning (e.g., daytime fatigue, ability to function at work/daily chores, concentration, memory, mood, etc.)?; Item 6 = How noticeable to others do you think your sleeping problem is in terms of impairing the quality of your life?; Item 7 = How worried/distressed are you about your current sleep problem?
  2. *p < .05, **p < .01, ***p < .001