How do the prevalence and relative risk of non-suicidal self-injury and suicidal thoughts vary across the population distribution of common mental distress (the p-factor)? Observational analyses replicated in two independent UK cohorts of young people

Objectives: To inform suicide prevention policies and responses to youths at risk by investigating whether suicide risk is predicted by a summary measure of common mental distress (CMD, (the p-factor)) as well as by conventional psychopathological domains; to define the distribution of suicide risks over the population range of CMD; to test whether such distress mediates the medium-term persistence of suicide risks. Design: Two independent population-based cohorts. Setting: Population-based in two UK centres. Participants: Volunteers age 14-24 years recruited from primary health care registers, schools and colleges, with advertisements to complete quotas in age-sex-strata. Cohort 1 is the Neuroscience in Psychiatry Network (NSPN; N=2403); Cohort 2 is the ROOTS sample (N=1074). Primary outcome measures: Suicidal thoughts (ST) and non-suicidal self-injury (NSSI). Results: We calculated a CMD score using confirmatory bifactor analysis and then used logistic regressions to determine adjusted associations between risks and CMD; curve-fitting was used to examine the relative prevalence of suicidal thoughts (ST) and non-suicidal self-injury (NSSI) over the population distribution of CMD. We found a dose-response relationship between levels of CMD and risk of suicide. The majority of all subjects experiencing ST and NSSI (78% and 76% in Cohort 1, and 66% and 71% in Cohort 2) had CMD scores no more than two standard deviations above the population mean; higher scores indicated the highest risk but were, by definition, infrequent. Pathway mediation models showed that CMD mediated the longitudinal course of both ST and NSSI. Conclusions. NSSI and ST in youths reflect common mental distress that also mediates their persistence. Universal prevention strategies reducing levels of CMD in the whole population without recourse to screening or measurement may prevent more suicides than approaches targeting youths with the most severe distress or with psychiatric disorders.