Field Experiments. Parke, Berkowitz, and Leyens (1977) conducted a field experiment in a minimum-security penal institution for juveniles. The researchers exposed groups to unedited feature-length films that were either aggressive or nonaggressive. On the day after the last film was shown, in the context of a bogus learning experiment, the boys were told they had a chance to hurt a confederate of the experimenters who had insulted one group of boys and had been neutral to the other. The results on an electric shock measure similar to the one used in the Liebert and Baron (1972) study, described previously, revealed that the most aggressive of all the experimental groups were the boys who had seen the aggressive films and had been insulted. In addition to this laboratory measure, the investigators collected observational data on the boys’ aggressive interpersonal behavior in their everyday environment. These data showed that boys who saw the violent movies were more interpersonally aggressive. However, there was no apparent cumulative effect of movies on aggression. The boys who watched the diet of aggressive films were just as aggressive after the first film as after the last.
Figure 9.11 illustrates the design of the Canadian field experiment (Williams, 1986) discussed earlier. The dependent variable of aggression was measured in three ways: observations of behavior on school playgrounds, peer ratings, and teacher ratings. On the observational measure, the aggressive acts of children in the town labeled A (the town that just received TV) increased from an average of 0.43 per minute in Phase 1 to 1.1 per minute in Phase 2. Children in the other towns showed only a slight and statistically insignificant increase in the same period. Peer and teacher ratings tended to support the behavioral data. As yet, there have been no large-scale field experiments examining prosocial behavior.