The STAR collaborative nonsuicidal self-injury study: methods and sample description of the face-to-face sample.

Background: Nonsuicidal self-injury (NSSI) is highly prevalent in adolescents and young adults worldwide. It is linked to a broad variety of mental disorders and an increased suicide risk. Despite its high prevalence, research on the underlying mechanisms and on potential risk and resilience factors for maintaining or quitting NSSI remains scarce. This manuscript presents an overview of the "Self-injury: Treatment-Assessment-Recovery" (STAR) collaboration, which aimed to address these gaps.

Methods: We investigated the natural course of NSSI as well as its social, psychological, and neurobiological predictors (observational study; OS). OS data collection occurred at four timepoints (baseline [T0], 4 [post, T1], 12 [follow-up (FU), T2], and 18 [FU, T3] months after baseline) for the NSSI group, which was compared to a healthy control (HC) group at T0 only. Online self-report was used at all timepoints, while semi-structured interviews (face-to-face (f2f)) were conducted at T0 and T3. At T0 only, we conducted ecological momentary assessment and neurobiological investigations. Here, we present the general methodology and sample characteristics of the completed OS including the f2f subprojects, while other subprojects are not within the scope of this paper.

Sample description: The OS sample consists of 343 participants at T0 (180 NSSI, 163 HC). Mean age in the NSSI group (T0) was 18.1 years (SD = 2.09, range: 15-25), gender-related data is available for 166: 156 = female, 7 = male, 3 = transgender, 10 = not disclosed). In the HC group, mean age (T0) was 19.1 years (SD = 2.35, range: 15-25) (142 = female, 21 = male). At T1, 128 (71.11%) of the NSSI participants completed the questionnaires, at T2 125 (69.44%) and at T3 104 (57.78%). In the fMRI subproject, 126 adolescents participated (NSSI = 66, HC = 60, 100% female; mean age (T0): NSSI = 18.10 years, SD = 2.21; HC = 19.08, SD = 2.36).

Conclusion: Understanding predictors is of utmost importance for adequate diagnosis and intervention for NSSI. Our OS applied a multimodal investigation of social, psychological, and neurobiological parameters and is the largest sample of adolescents with NSSI to date including follow-up assessments. As health care providers require specific knowledge to develop new treatments, we believe that our in-depth assessments can potentially enhance care for youths engaging in NSSI.