Debate regarding the psychological and behavioural effects of playing violent video games has recently led to claims that violent video games increase aggression effects in adolescents, and that this issue has now been settled. However, other researchers have found either no detrimental effects from game playing or even positive (cathartic) effects. In this research we demonstrate that these different conclusions are not mutually exclusive and can be explained by the method of assessment and analytic techniques utilised. We had adolescents play a violent video game (Quake II ) and took measurements of anger both before, during and after game play. The results demonstrated that some people increase, some decrease and the majority show no change in anger ratings. Unlike past research, we also demonstrate that these changes are mediated by the player's feelings immediately prior to game play and a labile temperament - one predisposed to aggression - and that these variables predict people's reactions with an average 73% concordance rate.