Bandura believed that the potential for aggression may be biological, but the expression of aggression is learned. The social-learning theory (SLT) states that learning occurs through observation of a model. Imitation of an observed behaviour is more likely if the model is someone we aspire to or identify with or if they are rewarded. This is vicarious reinforcement. A child forms a mental representation of an event, including the possible rewards or punishments of the behaviour. When a child imitates an aggressive behaviour, they gain direct experience, and the outcome of the behaviour influences the value of aggression for the child. If they are rewarded they are more likely to repeat the behaviour. Children develop self-efficacy, which is confidence in their ability to successful carry out a behaviour. If aggressive behaviour is unsuccessful for a child, they will have a lower sense of self-efficacy so are less likely to behave this way in future. There is strong empirical evidence to support the SLT. For example, Bandura’s Bobo doll studies found that children who observed a model behaving aggressively to the Bobo doll behaved more aggressively than those who observed a non-aggressive model and also imitated specific aggressive acts. This supports the theories claims that behaviour can be learned through observation. A criticism of this study is that it only used children participants, so we are unable to generalise these results to adults. However, Philips found that the daily homicide rate in America increases in the week after a major boxing match on TV, providing evidence of social learning in adults. An advantage of the SLT is that it can explain differences between individuals, e.g. cultural differences and also differences within individuals, which can be explained by selective reinforcement and context-dependent learning, which is when people have observed aggressive behaviour rewarded in one situation and not in another. A limitation of SLT is that it is not a complete explanation of aggression, as it can’t explain the impulse to aggress. After observing aggressive behaviour, people only behave aggressively if they are frustrated. It may also be accused of being reductionist, as it ignores biological factors such as testosterone levels. An alternative explantion is Zimbardo’s deindividuation theory, which states that aggressive behaviour is the result of a loss of personal identity and individuality. Factors that cause deindividuation include being in a large crowd, anonymity due to wearing a uniform and altered consciousness due to drugs or alcohol.