Most strikingly, the study found that the proportion of young servicemen (under 30 years old) with a conviction for violent offending was much higher than among men of a similar age in the general population (20.6% vs 6.7%).
"There has been a lot of media coverage and public debate about violence committed by veterans of the conflicts in Iraq and Afghanistan. Our study, which used official criminal records, found that violent offending was most common among young men from the lower ranks of the Army and was strongly associated with a history of violent offending before joining the military. Serving in a combat role and traumatic experiences on deployment also increased the risk of violent behaviour", explains Dr Deirdre MacManus from King's College London, who led the research.
The first large-scale study of its kind, linked data from 13,856 randomly selected serving and ex-serving UK military personnel with national criminal records to assess the impact of deployment (serving in Iraq or Afghanistan), combat exposure, and post-deployment mental health problems on subsequent offending behaviour.
The researchers found that 17% of male service personnel in the study had a criminal record. Whilst overall lifetime offending (all offences from theft to assault) in the military was lower than in the general population, lifetime violent offending (ranging from threats of violence to serious physical assault or worse) was more common among military men (11% vs 8.7%).
Pre-military history of violence, younger age, and lower rank were the strongest risk factors for violent offending. Men who were deployed to Iraq or Afghanistan with direct combat exposure were 53% more likely to commit a violent offence than men serving in a non-combat role. Witnessing traumatic events on deployment also increased the risk of violent offending.
Alcohol misuse, post-traumatic stress disorder (PTSD), and high levels of self-reported aggressive behaviour on return from deployment were also found to be strong predictors of subsequent violent offending.
According to Dr MacManus, "The findings provide information that can enable better violence risk assessment in serving and ex-serving military personnel. They draw attention to the role of mental health problems and the potential effect that appropriate management of alcohol misuse, post-traumatic stress disorder, especially hyperarousal symptoms, and aggressive behaviour could have in reducing the risk of violence.
Writing in a linked Comment, David Forbes, Director of the Australian Centre for Posttraumatic Mental Health, University of Melbourne, Australia and Richard Bryant from the University of New South Wales, Sydney, Australia say, "[These findings] show for the first time the link between combat and interpersonal violence…[and] draw attention to the need for a more concerted effort to understand the specific mechanisms that affect how the experiences of combat can enhance risk of violence after deployment. By understanding these factors, we might develop more informed prevention and intervention programmes for troops as they reintegrate into civilian life."