The questionnaire used in the study comprised a demographic section asking about date of birth (used for coding age), gender (here coded as: 1-male, 0-female). There were 122 items from five questionnaires, briefly described below (all items used in the bifactor model are listed in the Additional file
1). Six items were excluded as unsuitable for participants living with their parents and attending school or college (e.g., “I change jobs” or “I change residences”). The 24-item Inventory of Callous and Unemotional Traits (ICU [
22]) had a response scale from not at all (0) to definitely true (3) and 3 subscales measuring callous-unemotional and antisocial traits: Unemotional (5 items), Callousness (11 items), Uncaring (8 items). The 17-item Antisocial Process Screening Device (APSD [
23]) had a response scale from not at all true (0) to definitely true (2) and 3 subscales measuring narcissistic, callous-unemotional traits and impulsivity: Narcissism (7 items), Impulsivity (5 items), Callous-Unemotional (5 items). The 27-item Child and Adolescent Dispositions Scale (CADS [
24]) had a response scale from not at all (1) to very much (4) and 3 subscales measuring negative emotionality, risk taking and antisocial traits: Negative Emotionality (9 items), Daring (5 items), Prosociality (13 items). The 25- item Barratt Impulsiveness Scale (BIS [
25]) measuring various aspects of impulsivity trait had a response scale from rarely (1) to always (4) and 3 subscales: Nonplanning (11 items), Motor Impulsiveness (8 items), Attentional Impulsiveness (7 items). The 22-item Schizotypal Personality Questionnaire (SPQ [
26]) had binary response options: yes (1) and no (0), and 3 subscales measuring aspects of schizotypal trait related to cognitive and perceptual idiosyncrasies, social avoidance and social anxiety, and disorganised behaviour: Cognitive-Perceptual (8 items), Interpersonal (8 items), Disorganised (6 items).
The following measures were used as external validation criteria: the Cambridge Friendships Questionnaire (CFQ [
27]); the Moods and Feelings Questionnaire (MFQ [
28]); the Revised Children’s Manifest Anxiety Scale (RCMAS [
29]); the Revised Leyton Obsessional Inventory (R-LOI [
30]); the Antisocial Behaviour Questionnaire (ABQ [
31]); the Rosenberg Self-Esteem Scale (RSE [
32]); the Warwick-Edinburgh Mental Well-being Scale (WEMWBS [
33]), and also a retrospective measure of childhood experiences of parenting practices – the subscale of Positive Parenting from the Alabama Parenting Questionnaire (APQ [
34])
.