Witnessing gun violence can double the likelihood of a teenager committing serious violence in the following two years, suggests a new study by US researchers.

Although a connection between exposure to violence and violent behaviour has been previously suggested, it is difficult to show a direct causal link. But this study claims to have isolated the independent contribution made by actually witnessing gun violence by comparing over 1500 teenagers with a similar likelihood of being exposed to violence.

“Based on this study’s results, showing the importance of personal contact with violence, the best model for violence may be that of a socially infectious disease,” says Felton Earls, at Harvard Medical School, US, who led the study. “Preventing one violent crime may prevent a downstream cascade of ‘infections’.”

Previous studies have shown a link between child abuse or violence in the home and violent behaviour outside the home. “But it’s not been so clear that community violence carries the same implications,” he told New Scientist. “Our study clarifies doubt that exposure to community violence is indeed part of the contagion process.”

Walking away

“It suggests that the classic public health approaches to the control of infectious disease – such as vaccination – might have useful analogues in violence prevention,” adds Jeffrey Bingenheimer, also on the team.

“For every specific act of violence [that violence prevention] programmes prevent, they may also prevent a chain reaction of violence among those who would have been exposed to that violent act,” he told New Scientist.

Earls suggests that school-based programmes which teach children how to deal with conflict without resorting to fighting may help. “In some cases it means just walking away from somebody you just want to smack – and showing that can be done with dignity.”

The five-year study, which started in the early 1990s spurred by an “epidemic” of violent crime in the US, tracked adolescents aged 12 or 15 from 78 Chicago neighbourhoods. To tease out the effects of witnessing violence on subsequent violent behaviour the team controlled for 153 potentially influential variables, such as family structure and neighbourhood.

This allowed the sample to be split into two groups, Earls explains, with just one major difference between them – one group had witnessed gun violence but the other group had not.


The children and their parents or primary carers were interviewed on three occasions over a five-year period. In the two years after witnessing gun violence, “the exposure group were two to three times more likely to engage in violent behaviour themselves”, he says.

“When individuals have such traumatic experiences – witnessing or being exposed to gun violence – it makes them hyper-vigilant,” says Daniel Webster, co-director of the Center for Gun Policy and Research at the Johns Hopkins Bloomberg School of Public Health in Baltimore, US.

“There are often social stimuli that are ambiguous – like at a crowded party, someone bumps into you. How do you interpret those stimuli?” he asks. Webster suggests that people exposed to violence may be more prone to assume a hostile intent – as a self-defence mechanism – which could in itself lead to violence.

More here.