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Frustration–aggression hypothesis, otherwise known as the frustration–aggression–displacement theory, is a theory of aggression proposed by John Dollard, Neal E. Miller et al. in 1939, and further developed by Miller et al. in 1941 and Leonard Berkowitz in 1969. The theory says that aggression is the result of blocking, or frustrating, a person's efforts to attain a goal.
The frustration–aggression hypothesis attempts to explain why people scapegoat. It attempts to give an explanation as to the cause of violence. The theory, developed by John Dollard and colleagues, says that frustration causes aggression, but when the source of the frustration cannot be challenged, the aggression gets displaced onto an innocent target.
There are many examples of this. If a man is disrespected and humiliated at his work, but cannot respond to this for fear of losing his job, he may go home and take his anger and frustration out on his family. This theory is also used to explain riots and revolutions, which both are believed to be caused by poorer and more deprived sections of society who may express their bottled up frustration and anger through violence. 
According to Yale Group, frustration is the "condition which exists when a goal-response suffers interference," while aggression is defined as "an act whose goal-response is injury to an organism (or an organism surrogate)."However, aggression is not always the response to frustration. Rather a substitute response is displayed when aggressive response is not the strongest on the hierarchy. Furthermore, this theory raises the question if aggression is innate.
However, the presented theory has some problems. First, there is little empirical support for it, even though researchers have studied it for more than sixty years.  Another issue is that this theory suggests frustrated, prejudiced individuals should act more aggressively towards out-groups they are prejudiced against, but studies have shown that they are more aggressive towards everyone. 
The theory also has limitations, for example it cannot say why the specific out-groups were chosen to be scapegoats and why others are not.
The frustration–aggression theory has been studied since 1939, and there have been modifications. Dill and Anderson present a study that questions whether frustration that is justified or not plays a role in future aggression. The experiment consisted of three groups of subjects performing a folding origami task that was timed. The participants were split into the control, justified frustration and unjustified frustration groups. In each condition the experimenter states how they will only present the instructions one time and then start the timer. At a predetermined fold the confederate in the condition interrupts the experimenter and asks them to please slow down.
In the unjustified group, the experimenter responds, “I cannot slow down. My girlfriend/boyfriend is picking me up after this and I do not want to make them wait.” In the justified condition the experimenter responds, “I cannot slow down. My supervisor booked this room for another project afterwards and we must continue.” Finally, the experimenter in the control condition responded, “Oh, okay I did not realize I was going too quickly. I will slow down.”
The subjects were then given questionnaires on their levels of aggression as well as questionnaires about the quality of the research staff. They were told that these questionnaires would determine whether the research staff would receive financial aid, or verbal reprimands and a reduction in financial awards. The questions presented on the questionnaire were designed to reflect the research staff's ability and likeability.
Dill and Anderson found that participants in the unjustified frustration group rated the research staff to have less ability and likeability, knowing this would affect their financial situation as graduate students. The justified frustration group rated the staff as less likeable and having less ability than the control group, but more than that of the unjustified frustration group. These results support the hypothesis that frustration can lead to aggression. This study presents data concerning behavioral aggression and frustration level.
- Dollard, John; Doob, Leonard W; Miller, Neal E; Mowrer, Orval Hobart; Sears, Robert R (1939). Frustration and Aggression. New Haven, CT, US: Yale University Press. OCLC 256003.
- Miller, N. E.; et al. (1941). "Symposium on the Frustration-Aggression Hypothesis". Psychological Review. 48 (4): 337–366. doi:10.1037/h0055861. APA
- Berkowitz, Leonard (1969). The frustration-aggression hypothesis revisited, in: Berokowitz (ed.), Roots of aggression, Atherton Press, New York
- Friedman, H., & Schustack, M. (1999). Personality classic theories and modern research. (Fifth ed., pp. 204-207). Pearson.
- Whitley & Kite 2010.
- Pastore, Nicholas (1950). "A Neglected Factor in the Frustration-Aggression Hypothesis: A Comment". The Journal of Psychology. 29 (2): 271–279. doi:10.1080/00223980.1950.9916032.
- Dill & Anderson 1995.
- Dill, J. C.; Anderson, C. A. (1995). "Effects of Frustration Justification on Hostile Aggression". Aggressive Behavior. 21 (5): 359–369. doi:10.1002/1098-2337(1995)21:5<359::aid-ab2480210505>3.0.co;2-6.