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 factor was then split into two factors, resulting in a four-factor model (social influence, automatic functions, peer identification and avoiding demands), which showed excellent fit to the data in the confirmatory factor analysis. Study IV (n = 816) showed that NSSI frequency, gender (female), self-reported experience of emotional and physical abuse, having made a suicide attempt, prolonged illness or handicap and symptoms of depression and dissociation were significant predictors in the final model of the automatic functions, indicating that these variables are important in understanding the mechanisms underlying the need to engage in NSSI to regulate emotions, generate feelings, gain control or to self-punish. Symptoms of depression and dissociation mediated the relationship between sexual, physical and emotional abuse and the automatic functions. Furthermore, frequency of NSSI, gender, emotional abuse, prolonged illness or handicap and symptoms of depression uniquely predicted automatic functions but not social functions. Self-reported experience of physical abuse, having made a suicide attempt, symptoms of anxiety and dissociation were significant in the final model of social functions, i.e., performing NSSI to influence or communicate with others, to avoid demands or to identify with peers. Of these, symptoms of anxiety were uniquely associated with social functions. Symptoms of anxiety and dissociation mediated the relationship between physical abuse and social functions of NSSI.

Taken together, this thesis has shown that NSSI is prevalent in Swedish adolescents and findings contribute to the discussion of a potential NSSI diagnosis. It is important to consider the effect of different types of negative life events and trauma symptoms in relation to NSSI in adolescents. Assessing the specific reinforcing functions of NSSI and the underlying factor structure can be helpful in developing functionally relevant individualized treatment.