Timing effects in the association between childhood and adolescent bullying victimisation with late adolescence and emerging adulthood depressive symptoms

Bullying victimisation during childhood is a significant risk factor for psychopathology, particularly depression, with some studies suggesting lasting associations into adulthood. However, these associations may vary based on developmental timing, i.e., age at exposure. Life course epidemiology proposes three timing hypotheses: (1) accumulation of risk, where additional exposure events increase impact; (2) recency, where proximal experiences have a greater impact than distal ones; and (3) sensitive periods, where specific timing windows increase vulnerability. These hypotheses have yet to be formally tested to better understand how the timing of bullying victimisation affects depression in emerging adulthood. This study explores the relationship between the timing of bullying victimisation and depression symptoms in late adolescence and emerging adulthood. Using data from the Avon Longitudinal Study of Parents and Children (N = 6,782), we applied the Structured Life Course Modelling Approach (SLCMA) to test accumulation of risk, recency, and sensitive period hypotheses. Bullying was measured with the Strengths and Difficulties Questionnaire at ages 4, 7, 8, 9, 11, 13, and 16. Depression symptoms were measured with the Short Mood and Feelings Questionnaire (SMFQ) at ages 16.5, 17.5, 21, 22, and 23. Developmental windows were defined as early childhood (0–5 years), middle childhood (6–10 years), early adolescence (11–14 years), and late adolescence (15–17 years). Model selection by SLCMA consistently favoured the recency hypothesis across outcome timepoints, such that exposure to bullying was associated with an increase in SMFQ at all ages between 4 and 16 years, with a greater increase for exposure to bullying at older ages: a unit increase in bullying victimisation score at age 4 was associated with an increase of 0.188 (95% CI: 0.160–0.260) in SMFQ score at age 16.5, while a unit increase at age 16 was associated with an increase of 0.753 (95% CI: 0.640–0.867). Findings suggest that the association between bullying victimisation and depressive symptoms is primarily driven by recency. Early post-exposure intervention is essential to reduce later mental health consequences.