A test of the interpersonal function of non-suicidal self-injury in daily life.

Theoretical models of non-suicidal self-injury (NSSI) posit that individuals use NSSI to influence others, but this remains largely untested. We used ambulatory assessment to test the interpersonal function of NSSI in the daily lives of 51 women with DSM-5 NSSI disorder. Participants reported NSSI events, urges, motives, and positive/negative interpersonal events (IPEs) for 14 days, providing five semi-random daily assessments and event-related NSSI reports. We analyzed 3,498 data-points, including 155 NSSI events, using multilevel models. We observed a positive concurrent association between the number of negative IPEs and NSSI engagement. Additionally, perceived distress of negative IPEs was positively associated with concurrent NSSI events and urges, and predicted later events. We saw no reduction in negative or increase in positive IPEs following NSSI. In a trait-level interview, participants endorsed interpersonal motives only minimally, but indicated that others often trigger NSSI. In daily life, participants rarely endorsed the motive 'get help/attention'. The results suggest that negative IPEs trigger NSSI, but that individuals in this sample rarely used NSSI for interpersonal motives and did not experience interpersonal reinforcement of NSSI. We discuss limitations of and possible solutions for under-reporting of interpersonal motives and benefits of studying interpersonal triggers (rather than outcomes) in future studies.