Aggression has been defined as any form of behaviour that is intended to harm another person (Passer, Smith, Atkinson, Mitchell and Muir, 2011). Over the years psychologists and other researchers have been able to study this form of behaviour by analyzing the factors that may contribute to aggression. These factors have been thought to include biological, environmental and psychological levels, which may work individually or all together in contributing to aggressive behaviours. Aggression can take place in various forms including physical aggression where the aggressor exhibits pushing, slapping and shooting other people or verbal aggression, in this form the aggressor may intimidate or engage in taunting and name-calling. The last form of aggression takes place indirectly and involves the aggressor taking part in behaviours such as gossiping, spreading rumors and encouraging others to exclude someone (Facts for teens: aggression, 2002). A wide variety of research has been done on aggressive behaviour in adolescents and it is still an ongoing process into understanding why some children are more predisposed to certain behaviours than others. Research that has been undertaken has discovered that children are more likely to engage in aggressive behaviour if they are exposed to the following risk factors: individual characteristics, home environment, relationships with peers, media violence, social failure, community factors and genetics (Facts for teens: aggression, 2002). Therefore, more research needs to be conducted in order to help understand why some children are more aggressive and to reduce or prevent the behaviour. Studies in the last few decades on aggression have particularly focused on the effects of the androgen hormones; testosterone and cortisol. Much of the research supports the idea that these two hormones do play a role in the expression of aggressive behaviour in young adolescents.
Yi-Zhen Yu and Jun-Xia Shi examined the effects of testosterone and cortisol hormone levels in saliva to examine whether the endocrinal factors contribute to the aggressive behaviour in adolescents. Their study included the participation of 20 aggressive youth, which was made up of 10 males and 10 females, as well as 20 non- aggressive students. The 40 participants were selected from a population of 1051 students all of whom were between the ages of 11- 16 years of age and from the province of Hubei in China. The groups were then further divided by age, gender, stage of pubertal development and economic status of their families. Once selected Yu and Shi evaluated aggressive behaviours using child behaviour check list (CBCL), along with a parent questionnaire. The use of the CBCL allowed the researchers to adhere to a standardized evaluation technique, consisting of the evaluation of behavioral problems and social competencies based on the reports from people who know the child well. The checklist allowed the researchers to examine a broad range of emotional and behavioral problems and identify two major groups of problem children- those that internalize problems (inhibited behaviour) and those that externalize problems (aggressive behaviour) (Yu & Shi, 2009). Using the questionnaire taken by the child’s guardian along with the rest of the CBCL, Yu and Shi were able to calculate a score for aggression. An aggressive child in this study was defined as having a score that was above or equal to China’s norms. In this case, for male an aggressive student was considered aggressive if their score was above 18, while for females the score had to be 17 or above. Yu and Shi also collected saliva samples from each individual, all at the same point during the day. The collected sample from each participant was examined and tested for the cortisol (CORT), testosterone (T) and growth hormones (GH) using radioimmunoassay, which measures the levels of each hormone. After testing was complete, Yu and Shi were able to compare the results from both groups to determine whether increased levels of the hormones were a contributing factor towards displays of aggressive behaviour.
Richard Tremblay and his colleagues focused on identifying the associations between testosterone level, physical development and a concurrent assessment of antisocial behaviour (Tremblay, Schaal, Boulerice, Arseneault, Soussignan, and Paquette, 1998). The subjects involved were made up of 1161 caucasian males with the mean age sitting at around 6.12 years. All the subjects chosen were from low socioeconomic areas in Montreal. For 57 of the boys who were between the ages of 12 and 13, data on testosterone, physical aggression and social dominance was available to use (Tremblay et. al., 1998). For behavioral measures, behaviour assessments were obtained from the children’s teachers at the ages of 6,10,11 and 12 years, from peers at 10,11 and 12 and from the boys themselves at 10, 11, 12, and 13 years of age. The teacher’s ratings were obtained using a Social Behaviour Questionnaire (SBQ) and scored on a three level scale consisting of “does not apply”, “applies sometimes” and “frequently applies” (Tremblay et. al., 1998). Two types of aggression- physical and opposition scores were derived from items such as “blames others”, “disobedient” and “fights”. The range of the scores for physical aggression was from 0-6 and for opposition aggression it was from 0-10. This testing was done at the end of every school year for the ages of 6,10,11 and 12 years of age. For peer ratings, Tremblay and his colleagues used the Pupil Evaluation Inventory that was used at ages 10,11 and 12. The evaluation involved each child in a class to nominate four students who fit the criteria for each item described on the questionnaire. From the questionnaire a score was derived that represented physical aggression. This score was generated from two criterions out of the thirty-five that were “those who start a fight over nothing” and “those that say they can beat everybody” (Tremblay et. al., 1998). For the self-assessments the boys answered a 27-item delinquency questionnaire at the ages of 10, 11, 12 and 13 years of age (Tremblay et. al., 1998). The questionnaire was made up of a four point rating scale (never, once, twice or often). Questions that were asked included “steals objects worth more than $10 in school”, “get drunk”, “set a fire”, “carries a weapon” and “takes money from home” (Tremblay et. al., 1998). The score from the 27 questions were used to obtain a self-reported physical aggression score. Hormonal measures were also obtained for the boys at the ages of 11,12, and 13 years of age. Saliva samples taken at three consistent times (8:30, 10 and 13:00 o’clock) were used to measure testosterone levels. The samples were then subjected to radioimmunoassay testing to obtain the testosterone levels of the boys. The testosterone levels in boys who were 11 years of age did not have a high enough detection limit and therefore their saliva sample was excluded in later statistical analyses. Physical measures included in the study involved height, wrist, weight and head circumferences for boys between the ages of 12 and 13.
The two studies are similar in the sense that they both focused on whether increased levels of testosterone were found in the more aggressive groups. However, both studies differed in how they were conducted. Yu and Shi focused more on the hormones that are present in aggressive adolescents with the use of testing hormone levels using saliva and the CBCL. The study conducted by Yu and Shi concluded that the cortisol (CORT) and testosterone (T) hormones are associated with adolescent aggressive behaviours. They also stressed that the endocrine factors do play a certain role in the display of aggressive behaviours. However, the study was not able to explain the mechanism, which underlies the occurrence due to external factors such as personality playing a certain role in aggressive behaviours. In the study done by Tremblay and his colleagues, their results concluded that testosterone levels and the individuals body mass were highly correlated with an individual displaying physical aggression. Other differences between the studies focused on different aspects of adolescence, with Tremblay and his colleagues choosing to use only male subjects to test aggression, while Yu and Shi chose to involve both males and females. Overall, Tremblay’s study concluded that boys with the largest body mass tended to be the most physically aggressive. The study also was able to show the link between testosterone and aggression, suggesting that the more testosterone that was present in the boy led to more physical aggression. However, Tremblay and his colleagues stressed that the positive association may be due to other factors, such as social dominance. The boys who had the greater need to dominate would be more likely to express physical aggressive behaviors and often times display them more frequently due to higher levels of testosterone.
Overall, both studies generally agreed that testosterone levels were higher among adolescents with aggressive behaviour. Thus, experiments done on aggression in adolescents may help lead to understanding how to predict aggressive behaviours early on in adolescents. This can therefore help to allow individuals and their families to create an environment where factors that lead to aggression can be lessened since individuals with higher testosterone levels are more at risk to display aggressive behaviours. In conclusion, more research is needed to help continue to support the idea that increased testosterone levels do lead to greater levels of aggression. Although both studies do support the idea that higher testosterone levels and higher body mass lead to more aggressive behaviours, the results are only correlational and more research would be needed to confirm these results. Research will need to create an understanding of why these individuals have an increased level of testosterone and ways to minimize the factors that can lead to these aggressive behaviours.
Facts for teens: aggression. (n.d.). National Youth Violence Prevention Center. Retrieved March 24, 2012, from www.herkimercounty.org/
Passer, M. W., Smith, R. E., Atkinson, M. L., Mitchell, J. B., & Muir, D. W. (2011). Memory.
Psychology: frontiers and applications (Fourth Canadian Edition ed., p. 300). United States
of America: McGraw- Hill Ryerson.
Tremblay, R. E., Schaal, B., Boulerice, B., Arseneault, L., Soussignan, R. G., Paquette, D., et al. (1998). Testosterone, physical aggression, dominance, and physical development in early adolescence. International Journal of Behavioral Development, 22(4), 753-777. Retrieved March 21, 2012, from the Sage Publisher database.
Yu, Y., & Shi, J. (2009). Relationship between levels of testosterone and cortisol in saliva and aggressive behaviours of adolescents. Biomedical and Environmental Sciences, 22, 44-49. Retrieved March 20, 2012, from http://www.besjournal.com/Articles/Archive/2009/No1/201110/P020111017345460659999.pdf