Public debate on the effects of violent video games can become especially contentious in the wake of a rampage shooting, such as the recent killing of nine people in Munich.

If it is later discovered the perpetrator was a fan of violent video games, as was the Munich killer, it is tempting to think that perhaps violent games “caused” the rampage shooting.

But rampage shootings are rare and complex events caused by multiple factors acting together. One can’t accurately predict a rampage shooting based on exposure to violent video games or any other single factor. But this doesn’t mean there isn’t a link between violent video games and aggression.

Experimental quandaries

Laboratory experiments are used to make firm and causal conclusions about violent video game effects. Here, researchers randomly assign participants to play a violent or nonviolent game, while holding all other variables (such as instructions given to participants) constant.

Although one can’t test whether violent video games cause violent criminal behaviour in laboratory experiments, researchers have conducted hundreds of experiments on less serious forms of aggression.

Aggression, which is any behaviour intended to harm someone, has typically been measured in labs using electric shocks. Researchers will look at the number, intensity and duration of shocks the person studied gives to a research accomplice pretending to be another participant in the video game.

Other studies have measured aggression by having participants punish accomplices in the games by blasting them with loud noise through headphones, forcing them to eat hot sauce and putting their arm in icy water.

In field experiments (conducted outside the lab) involving children, aggression has been measured by observing behaviours in interactions with other children, such as pushing, kicking, tripping and hitting.

Reviews of these experiments, called meta-analyses, show violent video games increase aggression in males and females of all ages, regardless of where they live. Violent games also desensitise players, making them numb to others’ suffering.

Aggression and violence

Lab experiments can’t be used in every instance. The researcher might not be able to control some variables (such as what video games participants play), to randomly assign participants groups (to play a violent or nonviolent game), or to measure violent behaviour, such as assault.

These difficulties could be overcome by conducting cross-sectional, correlational studies that measure the variables of interest (such as exposure to violent video games and aggressive behaviour) and potentially confounding factors (such as intellectual functioning and poverty). Measurements are taken at one point in time and analysed to see if they are correlated when confounding variables are controlled.

Longitudinal studies are like the correlational studies except researchers take multiple measurements on the same group over an extended period of time – months, years or decades. Longitudinal studies allow researchers to look at possible long-term effects of violent video games.

When different research methods yield similar results, one can have more confidence in them. Very similar results have been obtained for experimental, cross-sectional, and longitudinal violent video game studies.

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While there isn’t complete consensus in any scientific field, a study we conducted showed more than 90% of paediatricians and about two-thirds of media researchers surveyed agreed that violent video games increase aggression in children.

Additionally, several cross-sectional and longitudinal studies have found that while exposure to violent media isn’t “the” cause of extreme violent behaviour, they do increase the risk of such behaviour.

These do tend to find weaker relations for violent behaviour – which is a more extreme form of aggression that can lead to injury or death – than for aggressive behaviour.

This makes sense as violent behaviour is more difficult to predict because it is more rare and complex.

Theoretically, it makes sense

There are theoretical and practical reasons to believe exposure to violent video games is a risk factor for aggression and violence.

For decades, both therapists and researchers have argued that observing violence increases the likelihood of a child being aggressive, whether they observe it at home or school. Why would observing violence in mass media not have the same impact?

Of course, there is a difference between the virtual and real world, but no theory would predict that exposure to violent media should not impact the way children think, feel and behave.

Practically, most people are immersed in the media. American children between eight and 18 years spend more than seven and a half hours per day consuming mass media on average – more time than they spend in school.

Recent studies show American adults may spend even more time consuming media than children. Violence is a dominant theme in many forms of media, such as television and music, and I can’t think of an activity that people engage in for at least seven hours per day that would have no effect on the way they think and behave.

The human brain is plastic and its structure is shaped by experiences. Indeed, people expect to be affected by the media and if they are not they become bored and turn off the screen.

Exposure to media violence is also one of the few risk factors for aggression and violence that policymakers, professionals and parents can actually do something about. Other risk factors – such as being male or living in poverty – are much more costly and difficult (or even impossible) to change.

We might never know the cause of a shooting rampage such as the one in Munich. And while there is evidence that exposure to violent video games is linked to aggression, this does not always translate to violent behaviour. And it is rarer still for violent behaviour to translate to a mass shooting.