Table 1 Descriptive statistics of the total sample, test of gender differences, bivariate correlations between individual ISI items, and item-total correlations among male and female adolescents

Item 1

1.07

1.02

0-4

0.77

0.05

20.46***

.014

---

---

Item 2

0.65

0.97

0-4

1.51

1.60

7.40**

.005

---

---

Item 3

0.92

1.16

0-4

1.12

0.27

6.74*

.005

---

---

Item 4

1.03

0.96

0-4

0.94

0.50

25.80***

.017

---

---

Item 5

1.25

0.88

0-4

0.56

0.19

6.96**

.005

---

---

Item 6

1.14

0.97

0-4

0.84

0.46

3.44

.002

---

---

Item 7

0.61

0.89

0-4

1.61

2.43

11.40**

.008

---

---

ISI total score

6.67

4.39

0-27

1.00

1.13

25.91***

.017

21.02***

.12

Bivariate correlations

Item 1

Item 2

Item 3

Item 4

Item 5

Item 6

Item 7

Item 1

---

.43***

.27***

.58***

.25***

.17***

.39***

Item 2

.39**

---

.47***

.53***

.17***

.11**

.34***

Item 3

.25***

.43***

---

.36***

.13***

.12**

.28***

Item 4

.53***

.51***

.36***

---

.25***

.14***

.50***

Item 5

.23***

.24***

.16***

.34***

---

.47***

.30***

Item 6

.15***

.14***

.11**

.20***

.46***

---

.17***

Item 7

.42***

.34***

.25***

.48***

.33***

.27***

---

r_it

.50***

.54***

.39***

.64***

.44***

.32***

.54***