Young people who have had a schoolmate die by suicide are more likely to consider it or attempt it, according to a large Canadian study into "suicide contagion."

Suicide contagion refers to the ripple effect among pre-teens and teens who lose a schoolmate to suicide and then contemplate, attempt or die by suicide themselves.

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Ottawa Senators assistant coach Luke Richardson speaks on the issue of teen suicide during a news conference in February 2011 after his daughter Daron took her own life. A new study suggests school-wide interventions instead of targeting those who knew the suicide victim directly. (Sean Kilpatrick/Canadian Press)

For the study published Tuesday in the Canadian Medical Association Journal, researchers analyzed the association using survey data on 22,064 children aged 12 to 17 from across the country.

"Suicidality is of utmost public health concern, both as a predictor of suicide and because of its own burden on individuals and society," Dr. Ian Colman, Canada Research Chair in mental health epidemiology at the University of Ottawa and his co-author concluded.

Study respondents were asked whether anyone in their school had died and whether they personally know anyone who died by suicide. They were also asked if they'd seriously considered attempting suicide in the past year.

A schoolmate's suicide and personally knowing someone who died by suicide predicted suicidality in the study but the effect was stronger for the death of a schoolmate, the researchers noted.

"Our results support school-wide interventions over current targeted interventions" that focus on the close friends of the suicide victim, Colman and co-author Sonja Swanson from the Harvard School of Public Health in Boston said.

The risk was independent of previous depression or anxiety, social support and relationship with the victim.

By age 16 or 17, 24 per cent of teens had a schoolmate die by suicide and 20 per cent personally knew someone who died by suicide, which the researchers called consistent with national death statistics.

Most school strategies following a suicide typically last for months, which may not be long enough to truly reduce the risk of contagion, India Bohanna of School of Public Health at James Cook University in Cairns, Australia, said in a journal commentary published with the study.

The "suicide contagion" effect was less strong in older children, although those aged 14 and 15 exposed to suicide were still almost three times more likely to have suicidal thoughts, and those aged 16 and 17 were twice as likely.

The number of incidents of suicidal thoughts after a peer died was five times higher in those aged 12 and 13.

"The idea that suicide is contagious has always been controversial for various reasons; however, this important study should put many, if not all, doubts to rest," Bohanna said.

"We need to know what works in mitigating the risk of contagion and why."