Over the long term, being a bystander of high-school violence can be as damaging to mental health as being directly bullied, a new study finds.

Students who witness violence in school at age 13 are at later risk of psycho-social and academic impairment at age 15, according to a new longitudinal study by researchers at Université de Montréal with colleagues in Belgium and France.

In the study, published today in the Journal of Epidemiology and Community Health, Michel Janosz of UdeM’s School of Psycho-Education and his international team looked at a stratified cohort of nearly 4,000 Quebec high-school students. The researchers statistically tested the relationship between witnessing school violence in Grade 8 and subsequent antisocial behavior (drug use, delinquency), emotional distress (social anxiety, depressive symptoms), and academic adjustment (school achievement, engagement) in Grade 10. They also compared the relative contribution of differing forms of witnessing school violence and compared them to experiencing violence directly over the long term.

“Previous studies suspected that adolescents who witness violence might be at risk of experiencing post-traumatic psychological problems, but they could not rule out whether the students showing bystander effects were not already having such problems beforehand,” said Janosz noted.

“The Quebec cohort was ideal because we had psychological information on the students before witnessing the violence and this really makes a big difference scientifically in terms of rigor,” he continued. “There was less interference from confounders and other plausible explanations. Plus, we were able to follow up with the the students a couple of years later – a huge advantage.”

Added co-author Linda Pagani, also a professor at the School of Psycho-Education: “There were several take-home messages. First, witnessing school violence in Grade 8 predicted later impairment at Grade 10. Second, bystander effects were very similar to being victimized by violence directly.”