Background: Non-suicidal self-injury (NSSI) has attracted the attention of several clinicians and researchers due to its rising prevalence rates, its impact both on an individual and on a community level and more specifically, due to the possibility that it could form a distinct clinical category in the Diagnostic and Statistical Manual of Mental Disorders. Particular emphasis is given on accurately conceptualizing NSSI, which includes the risk factors leading to it. Although there are numerous studies supporting the role of early life experiences, attachment and emotion dysregulation, there is a lack of recent reviews investigating the contribution of all these factors together and a lack of studies investigating the interaction of all these factors, which might lead to NSSI engagement. Theorists and researchers investigating the interaction of two of the three aforementioned risk factors, suggest that the effect of early life experiences on NSSI might be serially mediated by attachment and emotion dysregulation. However, there is no study exclusively investigating this pathway. Additionally, it has been observed that the majority of studies examining the role of early life experiences have focused on basic forms of adversities, such as physical, sexual and emotional abuse, limiting in this way the scope of their effect. This demonstrates the need for a more inclusive measure, such as the Adverse Childhood Experiences-International Questionnaire, which has not been validated within a NSSI population.

Objectives: Therefore, the following thesis aimed: i) to provide a more recent systematic review and meta-analysis of the effects of early life experiences, attachment and emotion dysregulation (Systematic Review), ii) to investigate the proposed pathway leading to NSSI (Empirical Paper 1) and iii) to examine the psychometric properties of the ACE-IQ (Empirical Paper 2).

Results: Systematic Review - The findings from the systematic review and meta-analysis supported the effect of childhood maltreatment (d=0.271, p<0.001) and emotion dysregulation (d=0.198, p < 0.001) on NSSI. Although a significant effect was not demonstrated from the meta-analysis due to limited evidence (d=0.015, p=0.392), several studies supported the effect of insecure attachment on NSSI too. Empirical paper 1 - The proposed serial mediational model between early life experiences and NSSI via attachment and emotion dysregulation was supported [Indirect effect = 0.004, SE = 0.002, 95% CI (0.0007, 0.0090)]. Empirical paper 2 - The ACE-IQ was found to be a reliable (Cronbach’s alpha = 0.854) and valid measure (Convergent validity – r = 0.85, p<0.001 with the CTQ-SF; Predictive validity – R2 = 0.12, p=0.001 of the SHI total score; Discriminant validity – F-value = 13.90, p<0.001) to be used with individuals engaging in NSSI. However, some issues were identified with the factor structure of the ACE-IQ.

Conclusion: The findings were in accordance to previous theories and studies. Several research and clinical implications were discussed, such as the use of the proposed pathway for identifying individuals, who might be at risk of engaging in NSSI and for developing prevention strategies. Lastly, some suggestions were made for future studies, such as to expand the current proposed pathway by adding resiliency factors that might lead to NSSI engagement instead of suicide attempts. Additionally, a modification of the ACE-IQ was suggested to improve its subscales.