Non-Suicidal Self-Injury in Swedish Adolescents: Prevalence, Characteristics, Functions and Associations With Childhood Adversities

Non-suicidal self-injury (NSSI), such as intentionally cutting, burning or hitting oneself, is a behavior with potentially detrimental consequences and empirical studies are necessary to gain knowledge of how to prevent NSSI in adolescents. The aims of this thesis were to investigate the prevalence, methods, characteristics and functions of NSSI in a large community sample of Swedish adolescents, and to examine the relationship between NSSI and adverse life events and trauma symptoms. All empirical studies had a cross-sectional design and were based on 3,097 adolescents in the county of Östergötland, aged 15-17 years, in their first year of high school. Participating school classes were selected through a randomization process and administered self-report questionnaires. In study I (n = 3,060) a single item NSSI question resulted in a prevalence rate of 17.2%, while 35.6% of adolescents reported having engaged in NSSI at least once during the past year when given a checklist. The most commonly reported type of NSSI in this sample was “bit yourself”, followed by “hit yourself on purpose”, “erased your skin” and “cut or carved on your skin”. Applying the proposed DSM-5 diagnostic criteria of NSSI resulted in a prevalence rate of 6.7%. Results in study II (n = 2,964) showed that after controlling for gender, parental occupation and living conditions, adolescents with no self-injurious behavior reported the lowest level of adversities and trauma symptoms, while adolescents with both NSSI and suicide attempts (5.7%) reported the highest levels compared to those with only NSSI or a suicide attempt. Adolescents reporting frequent NSSI reported more adversities and trauma symptoms than those with less frequent NSSI. Automatic functions, such as affect regulation, self-punishment and feeling-generation, were the most commonly reported functions of NSSI. Attempts in study I to confirm Nock and Prinstein’s (2004) four-factor model of underlying factors of NSSI functions resulted in a close to acceptable fit. An attempt to refine the factor analysis on this community sample of Swedish adolescents, using Mplus with cross-validation, was made in study III (n = 836). An exploratory factor analysis resulted in a three-factor model (social influence, automatic functions and non-conformist peer identification), which was validated in confirmatory analysis. In order to adhere more closely to learning theory and the concept of negative and positive reinforcement, the third fa