Table 2 Characteristics of NSSI groups

Gender

 Girls

43 (78.2%)

41 (65.1%)

χ2(2) = 14.72

p < 0.001

Cramér’s V = 0.35

 Boys

6 (10.9%)

22 (34.9%)

 Non-binary

6 (10.9%)

0 (0%)

NSSI

 Age of onset, years M (SD)

11.83 (2.31)

11.16 (2.55)

t(51.8) = -1.15

p = 0.26

 One or more NSSI episode during last year

43 (78.2%)

23 (36.5%)

χ2(1) = 19.03

p < 0.001

Cramér’s V = 0.42

 Five or more NSSI episodes during last year^a

35 (63.6%)

14 (22.2%)

χ2(1) = 19.07

p < 0.001

Cramér’s V = 0.42

 Number of NSSI methods M (SD)

6.22 (2.29)

3.32 (2.26)

t(113.5) = -6.90

p < 0.001

d = 1.27

 Five or more NSSI methods^b

44 (80%)

16 (25.4%)

χ2(1) = 32.88

p < 0.001

Cramér’s V = 0.54

 Ever published their NSSI on social media

4 (7.3%)

0 (0%)

χ2 (1) = 1.76

p = 0.18

Cramér’s V = 0.19

Suicidality

 Suicidal ideation

42 (76.4%)

18 (28.6%)

χ2(1) = 24.96

p < 0.001

Cramér’s V = 0.48

 Suicide attempt

16 (29.1%)

2 (3.2%)

χ2(1) = 13.32

p < 0.001

Cramér’s V = 0.36

NSSI disclosure and help-seeking

 Disclosure to family

16 (29.1%)

3 (4.8%)

χ2(1) = 11.13

p < 0.001

Cramér’s V = 0.33

 Disclosure to friend(s)

28 (50.9%)

8 (12.7%)

χ2(1) = 18.46

p < 0.001

Cramér’s V = 0.41

 Disclosure to a professional

12 (21.8%)

0 (0%)

χ2(1) = 13.01

p < 0.001

Cramér’s V = 0.36

 Received professional mental health care/counseling

28 (50.9%)

16 (25.4%)

χ2(1) = 7.12

p < 0.01

Cramér’s V = 0.26

 Received professional help regarding NSSI

14 (25.5%)

3 (4.8%)

χ2(1) = 4.71

p < 0.05

Cramér’s V = 0.25

Emotion regulation and self-criticism

 DERS-16 M (SD)

51.53 (14.72)

39.54 (14.32)

t(112.9) = -4.47

p < 0.001

d = 0.83

 SRS M (SD)

34.98 (10.9)

24.83 (9.19)

t(106.2) = -5.43

p < 0.001

d = 1.01

Quality of life

 KIDSCREEN-52 M (SD)

150.26 (25.31)

175.08 (26.67)

t(113.8) = 5.16

p < 0.001

d = 0.95