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Biological studies (Evaluation: (The study benefits from taking ratings…
Biological studies
Evaluation:
The study benefits from taking ratings from two different sources: teachers and peers. this makes the findings more valid as it eliminates bias. the fact that the teachers and peers were in good agreement also adds to the validity.
the findings of the study could be used to prevent socially aggression; if children show physical aggressive tendencies then dealing with this may prevent them later showing social aggression. It could act as an early indicators for parents or teachers allowing them to intervene before the behaviour becomes too severe.
The sample size was small when looking at different groups. this makes generalization difficult because the chance of the sample being representative of the whole population is small. The reason for the small sample was because the researchers had to record the data individually from the 6yr old peers which is time consuming.
There could be many extraneous variables in the lives of the twins that may explain the aggressive behaviour shown. Another problem with generalising is the fact that the age group is very specific so it is hard to assume that aggression in other age groups will have the same cause.
Evaluation
This was the largest sample of severely violent offenders to be studied in this way and compared to matched controls, meaning there is a good degree of validity.
An effort was made to eradicate the effects of medication on the brain by keeping them drug free for 2 weeks. Also, researchers also made an effort to rule out confounding variables such as whether they were left or right handed
However, the study only represents a small sample of violent offenders as those pleading NGRI are not representative and therefore it cannot be taken as a representative explanation of violence. The study focused specifically on a sub-group of violent offenders, but the findings cannot be used as an explanation of other types of violence.
Procedure:
There were 234 twins. Data was gathered longitudinally at 5, 18, 30,48 and 60 months and then again at the age of 6yrs. Their teacher and their classmates were asked to rate them on their behaviour.
Teachers ratings were based on statements such as 'to what extent does the child to make others dislike a child' and 'to what extent does the child get into fights?' and it was based on a 3 point scale (0=never 1=sometimes and 2=often).
Classmates were giving booklets with pictures of every child in the class and then the children were asked to circle the pictures that matched the behaviour descriptions for example 'tells others not to play with others' or 'gets into fights'. Each child was given an overall rating score.
Results:
There were much higher correlations between the MZ twins on physical aggression than the DZ twins. On the other hand, the social aggression scores were roughly equally correlated between the MZ and DZ twins. This suggests that physical aggression is caused by genetics whereas, social aggression may be better explained by environmental factors.
A correlation was found between physical and social aggression in the children that was best explained by genes rather than the environment.
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Procedure:
There were two groups. the first group as a group of criminals who were pleading NGRI. Some had a Sz, had substance abuse or a learning disability. All p's remained medication free for 2 weeks prior to the PET scans. The control group was matched on age and gender and they were screened for general health.
All P's were given a continuous performance task (CPT) to complete which consisted of a sequence of blurred numbers to focus on. The P's were injected with FDG and after doing the CPT for 32 mins, a PET scan was done to look at the metabolic rate in different parts of the brain.
Raine et al
Aim: He wanted to see whether P's pleading NGRI would show brain dysfunctions in areas of the brain associated with violence such as the angular gyrus, thalamus and hippocampus.
Results:
The murderers showed lower activity in the prefrontal cortex and lower activity in the parietal areas. As well as higher activity in the occipital lobe and identical activity in the temporal lobe. They also had higher activity in the thalamus.
Conclusions:
These brain differences have been associated with many behavioural changes that could related to violent behavior. For example, dysfunction in the prefrontal cortex has been related to impulsivity.
Brendgen et al
Aim: to see if social aggression could be caused by genes or the environment. To see whether social aggression shared the same cause as physical aggression and to see if one type of aggression leads to another type.
Conclusions:
Strong genetic component to physical aggression but not social aggression. Children who were physically aggression were also more likely to be socially aggressive.