Violence may be a 'socially infectious disease'

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.