Do the victims of school bullies tend to become depressed later in life? A systematic review and meta‐analysis of longitudinal studies

Purpose The purpose of this paper is to investigate the extent to which bullying victimization in school predicts depression in later life and whether this relation holds after controlling for other major childhood risk factors. Design/methodology/approach As no previous systematic review has been conducted on this topic, effect sizes are based on both published and unpublished studies: longitudinal investigators of 28 studies have conducted specific analyses for the authors' review. Findings The probability of being depressed up to 36 years later (mean follow‐up period of 6.9 years) was much higher for children who were bullied at school than for non‐involved students (odds ratio (OR)=1.99; 95 per cent CI: 1.71‐2.32). Bullying victimization was a significant risk factor for later depression even after controlling for up to 20 (mean number of six covariates) major childhood risk factors (OR=1.74; 95 per cent CI: 1.54‐1.97). Effect sizes were smaller when the follow‐up period was longer and larger the younger the child was when exposed to bullying. Finally, the summary effect size was not significantly related to the number of risk factors controlled for. Originality/value Although causal inferences are tentative, the overall results presented in this paper indicate that bullying victimization is a major childhood risk factor that uniquely contributes to later depression. High quality effective anti‐bullying programmes could be viewed as an early form of public health promotion.