<p>Non-suicidal self-injury (NSSI) is a relatively common behaviour in adolescents. This is concerning as NSSI is a transdiagnostic risk factor for a range of mental disorders and is associated with increased risk of later suicide attempts. In this thesis, I used a longitudinal sample of New Zealand secondary school students to investigate the possible developmental pathway of parental attachment to NSSI via the mediating effect of emotion regulation. First, I examined the suitability of the

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... tion Regulation Index for Children and Adolescents (ERICA; MacDermott et al., 2010) as a measure of emotion regulation in a New Zealand sample using confirmatory factor analysis, followed by a comparison with a more popularly used measure (the Difficulties in Emotion Regulation Scale; Gratz & Roemer, 2004). Finding the ERICA to be suitable for use with my sample, I conducted a cross-lagged panel analysis with a longitudinal mediation to investigate how attachment, emotion regulation, and NSSI relate to each other over time. I found that emotion regulation was a significant mediator of the relationship between attachment and NSSI, supporting my hypothesis. The theoretical and practical implications of this are discussed in terms of the development of NSSI and intervention and treatment possibilities.</p>