Self-, other-, and dual-harm during adolescence: a prospective-longitudinal study of childhood risk factors and early adult correlates

Background Little is known about the childhood antecedents and adult correlates of adolescent dual-harm (i.e. co-occurring self- and other-harm). We examine the longitudinal associations between (a) social and psychological risk factors in childhood and adolescent dual-harm and (b) adolescent dual-harm and social and mental health impairments in early adulthood. Methods Participants (N = 1482) are from a prospective longitudinal community-representative study. Dual-, self-, and other-harm were self-reported at ages 13, 15, and 17. Social and psychological risk factors in childhood were assessed between 7 and 11; early adult correlates at age 20. Groups with dual-harm, self-harm only, other-harm only, and no harm were compared. Results Between 13 and 17, 7.2% of adolescents reported dual-harm (self-harm only: 16.2%; other-harm only: 13.3%). Some childhood risk factors (e.g. sensation-seeking, parental divorce, victimization by peers) characterized all harm groups; others were common to the dual- and self-harm (anxiety/depressive symptoms, relational aggression) or dual- and other-harm groups only (low self-control, substance use, delinquency). Adolescents with dual-harm had reported more physical aggression and harsh parenting, and lower school bonding in childhood than any other group. In early adulthood, they reported more anxiety/depressive symptoms, psychopathy symptoms, homicidal ideations, delinquency, and victimization experiences than any other group. Conclusions Adolescent dual-harm follows psychological problems and social disconnection in childhood and signals risk of psychopathology and isolation in early adulthood. To curb the burden from dual-harm, interventions must target adolescents, families, peer networks, and school environments. Differentiating youth with dual-harm from those with single-harm is important for developing personalized treatments.

From the Social Behavior Questionnaire (Murray, Obsuth, Eisner, & Ribeaud, 2019;Tremblay et al., 1991) 8 items During the past month, how often have you felt the following?
• I had to cry.
• I was scared. 1 = never to 5 = very often 0.79 Mean score (possible range: 1-5) Low self-control, age 11 From the self-control scale (Grasmick, Tittle, Bursik, & Arneklev, 1993) 10 items This is about how you see yourself. Mark how true these statements are for you.
• I often act on the spur of the moment without stopping to think. • If I don't get something I want immediately, I get angry pretty quickly. • I like to get out and do things more than I like to read or contemplate ideas.  (Murray, Obsuth, et al., 2019;Tremblay et al., 1991) these things you have done in the last 6 months.
• When you were mad at another kid, you said bad things about him/her behind the kid's back. • When you were mad at another kid, you got others to dislike that kid as well. Physical aggression (perpetration), age 11 From the Social Behavior Questionnaire (Murray, Obsuth, et al., 2019;Tremblay et al., 1991)  Adapted from (Wetzels et al., 2001) 2 items In the past 12 months, have any of the things below happened to you?
• Someone purposely injured you with a weapon (e.g., a knife) or object (e.g., a cane) or by repeatedly kicking you with heavy shoes. • Someone hit you so hard that they injured you (e.g. drawing blood or causing a black eye) without using a weapon or objects.

Variable descriptions
Socio-demographic variables were sex (1 = male, 0 = female), parental education background (1 = at least one parent with a tertiary educational degree, 0 = both parents with a lower or no degree), parental migration background (1 = both parents born abroad, 0 = at least one parent born in Switzerland), and child's educational level at age 13 (1 = high, 0 = low). In Switzerland, children are tracked into different educational levels at ages 12/13 and 15/16.
Here we use an indicator of whether the respondents followed an academic track by age 13 (called "high") or a lower track.

Associations with dual-and single-harm between ages 13 and 17
Sex differences in dual-and single-harm are described in the main manuscript. Parental educational background was not associated significantly with either dual-harm or other-harm only. However, low parental educational background was associated with a higher risk of selfharm only (17.6% of those with a low parental educational background reported self-harm only, compared to 12.6% of those with a high parental educational background; OR = 1.49, 95% CI = 1.01-2.18, p = 0.042). Parental migration background was not associated with dual-or single-harm. Dual-harm was more prevalent among adolescents following a lower educational track at age 13 compared to those in the higher track (8.8% vs. 6.0%; OR = 1.51, 95% CI = 1.01-2.25, p = 0.043). Single-harm was not significantly related to child educational level.   we did not enter all risk factors simultaneously into the models. Figure S1. Sensitivity analysis of early adulthood correlates of dual-and single-harm, with age-11 other-harm being included in the coding of harm groups.