A systematic review of interpersonal processes and their measurement within experience sampling studies of self-injurious thoughts and behaviours

Self-injurious thoughts and behaviours (SITBs) are a leading cause of death, and interpersonal processes (IPs) appear to play a role in SITBs. This systematic review synthesises the literature on IPs and SITBs in daily life and addresses four critical questions: (1) Which IPs have been assessed and how, (2) How are differences in IPs between individuals associated with SITBs?, (3) How are differences in IPs within individuals associated with SITBs? and (4) Do IPs relate differently to self-injurious thoughts than behaviours? Our review followed PRISMA guidelines and eligible literature was screened until 25 April 2024. We identified 58 Experience Sampling studies (32.76% daily-diary studies) of which most focused on IPs from major SITBs theories (e.g., thwarted belongingness) but largely used inconsistent operationalizations. Results from 39 studies investigating within-person associations were mixed. Based on 26 studies, whether differences in IPs between individuals relate to SITBs remains unclear. Three studies have investigated whether IPs relate to the transition from thoughts to behaviours, but temporal models are needed to draw firm conclusions. Studies investigating IPs and SITBs in daily life are largely inconclusive. Psychometrically validated measures are warranted, and future daily-life studies would benefit from drawing on ideation-to-action frameworks.