Table 1 Internal consistencies (Cronbach’s alphas, α), descriptives, and group differences for the sub-dimensional, dimensional and the total scores of the Youth Psychopathic traits Inventory (YPI) in 15- to 16-year-old Finnish and Dutch boys and girls

Finnish boys

Dutch boys

Finnish boys (n = 174)

Dutch boys (n = 221)

Statistics

α

α

Mean (SD)

Median

Mean (SD)

Median

U

p

Cohen’s d

YPI sub-dimension

 Dishonest charm

0.81

0.74

1.81 (0.67)

1.80

2.02 (0.65)

2.00

15,325.50

0.001

−0.318

 Grandiosity

0.79

0.81

1.89 (0.68)

1.80

1.86 (0.77)

1.75

18,074.50

NS

0.041

 Lying

0.82

0.72

1.80 (0.67)

1.80

2.01 (0.65)

2.00

15,343.00

0.001

−0.318

 Manipulation

0.86

0.81

1.70 (0.69)

1.60

1.98 (0.71)

1.80

14,399.00

<0.001

−0.440

 Remorselessness

0.83

0.63

1.69 (0.64)

1.60

2.01 (0.61)

2.00

12,963.00

<0.001

−0.440

 Unemotionality

0.65

0.50

2.15 (0.63)

2.20

2.24 (0.55)

2.20

1741.00

NS

−0.152

 Callousness

0.41

0.25

2.23 (0.51)

2.20

2.52 (0.46)

2.40

13,308.50

<0.001

−0.440

 Thrill-seeking

0.80

0.55

2.55 (0.72)

2.60

2.78 (0.57)

2.80

15,541.50

0.001

−0.353

 Impulsiveness

0.73

0.62

2.14 (0.67)

2.00

2.37 (0.62)

2.40

15,298.00

<0.001

−0.440

 Irresponsibility

0.74

0.60

1.85 (0.70)

1.80

1.85 (0.67)

1.80

18,782.00

NS

0.000

YPI dimension

 Interpersonal

0.90

0.85

7.19 (2.37)

7.00

7.88 (2.31)

7.40

15,686.50

0.002

−0.294

 Affective

0.55

0.61

6.07 (1.30)

6.00

6.77 (1.24)

6.80

12,756.50

<0.001

−0.440

 Behavioral

0.86

0.71

6.54 (1.84)

6.35

7.01 (1.44)

6.80

15,886.50

0.003

−0.285

 YPI Total

0.84

0.74

19.81 (4.91)

19.60

21.66 (4.18)

21.25

14,360.00

<0.001

−0.440

Finnish girls

Dutch girls

Finnish girls (n = 198)

Dutch girls (n = 253)

Statistics

α

α

Mean (SD)

Median

Mean (SD)

Median

U

p

Cohen’s d

YPI sub-dimension

 Dishonest charm

0.82

0.75

1.72 (0.66)

1.60

1.72 (0.60)

1.60

24,243.00

NS

0.000

 Grandiosity

0.82

0.76

1.58 (0.61)

1.40

1.34 (0.48)

1.20

18,940.00

<0.001

0.437

 Lying

0.77

0.78

1.64 (0.60)

1.40

1.64 (0.62)

1.40

24,980.50

NS

0.000

 Manipulation

0.81

0.77

1.62 (0.63)

1.40

1.57 (0.57)

1.40

24,491.50

NS

0.083

 Remorselessness

0.78

0.63

1.43 (0.52)

1.33

1.59 (0.52)

1.40

19,669.50

<0.001

−0.308

 Unemotionality

0.65

0.57

1.79 (0.54)

1.70

1.71 (0.47)

1.60

23,036.00

NS

0.158

 Callousness

0.44

0.46

1.67 (0.48)

1.60

1.89 (0.52)

1.80

18,583.00

<0.001

−0.440

 Thrill-seeking

0.78

0.72

2.47 (0.65)

2.55

2.51 (0.64)

2.40

24,538.00

NS

−0.062

 Impulsiveness

0.77

0.71

2.20 (0.67)

2.20

2.32 (0.64)

2.20

22,805.50

NS

0.183

 Irresponsibility

0.68

0.59

1.60 (0.57)

1.40

1.56 (0.51)

1.40

24,746.00

NS

0.074

YPI dimension

 Interpersonal

0.87

0.83

6.56 (2.12)

6.20

6.28 (1.86)

5.80

23,538.00

NS

0.140

 Affective

0.73

0.61

4.89 (1.24)

4.60

5.18 (1.11)

5.00

20,389.00

0.001

−0.246

 Behavioral

0.80

0.76

6.27 (1.59)

6.20

6.39 (1.47)

6.20

23,852.00

NS

−0.078

 YPI Total

0.77

0.76

17.71 (4.18)

17.10

17.84 (3.72)

17.20

24,342.00

NS

−0.032