Kids and adolescents playing violent video games can become more aggressive, a new study released Friday shows according to dpa. The findings, which are based on a review of the last 20 years of research, were presented to the annual convention of the American Psychological Association in Washington. Playing violent games for even a short period of time can lead to more aggressive behaviour, said researchers Jessica Nicoll and Kevin Kieffer of Florida's Saint Leo University. Their study shows that children playing violent video games were deemed more hostile by their teachers, more likely to get into fights and more likely to challenge authority figures. Kids playing these games "tend to imitate the moves that they just 'acted out' in the game they played," Kieffer said. While the researchers determined that more boys play these games than girls, it showed that aggressiveness also increases for those girls that play them. The two researchers lauded current practice of rating games, which prevents young children from buying them, but they said more research is needed "to explore why many children and adolescents prefer to play a violent video game rather than play outside, and why certain personalities are drawn to these types of games".