Personality refers to the traits of an individual that make their behaviors constant in all conditions. Hans Eysenck proposed a theory of criminal behavior that relied on personality. In his theory, criminal behavior is a result of interaction of several processes (Hayes, 2000). In the first place, he proposed that the difference in the personalities of individuals is dependent on two factors which are related to the inherent functioning of that person’s nervous system.
An individual’s degree of extraversion (E), neuroticism (N) can be determined by use of easy questionnaires like the Eysenck personality disorder (EPD). Individuals with a high score of E are social, outgoing, and chatty and look for sensations. The degree of arousal in an individual’s central nervous system and autonomic nervous system determines the E score. Persons who post a high E score are characterized by low levels of stimulation hence require more arousal from their surroundings. Having a high score of N give characteristic such as anxiety, depression and a powerful reaction to intrusive stimuli. N is caused by the general level of labiality in an individual’s central nervous system. Low score of N is characterized by a stable and inert nervous system, while a high score leads to instability.
Later on, he derived another aspect of personality called psychotism, (P). Individuals with a high score of this dimension are not sociable, aggressive, evasive and self-centered (Engler, 2008). He failed to illustrate the relationship between P and the working of the nervous system. Eysenck postulated that E, N and P result from the genetic makeup of a person (Hayes, 2000). In short, this theory shows that offenders generally, will exhibit a low degree of E (cortical stimulation), high level of N (autonomic stimulation) are more grounded in the psychotic perspective.
The traits theory is an exaggerated Eysenck theory. It postulates that criminal behaviors result from abnormal biological or psychological characteristics (Siegel, 2009). This theory has its foundations on the Italian criminologist by the name Cesare Lombroso. According to him, criminal are atavist. By the use of this term he meant that criminals are ancient beings resembling Neanderthal man, but are born into the current, world. To him, criminals belong to the past eras. According to this theory, there are distinguishable features that are related to the ancestors of man, these include: tiny heads, elongated ears, disarranged teeth, barrel thorax, and unbalanced arms.
The major shortcoming of this trait theory is that modern criminals are diverse. Modern trait theorists show that criminality cannot be determined by a physical or biological trait, each criminal has characteristics that determine their behavior. Modern understanding has many possibilities: inheritance of criminal traits, neurological challenges and having hematological disorders that predispose them to criminal activities. There is definitely a relationship between behavioral characteristics and biochemical changes in the brain and the nervous system.
Biocriminologists argue that criminality is genetically encoded. According to them, the normal functioning of the body including the brain requires a constant amount of nutrients and chemicals. Instability of these components results in psychological and learning problems which lead to anti-social traits (Siegel, 2009). Studies have associated low levels of glucose in the blood to violent traits and exaggerated levels of testosterone which leads to aggressive behaviors. Other physiological factors that are related to criminal behaviors are low levels of neurotransmitter, serotonin, low autonomic stimulation, and abnormal prefrontal cortical performance (Engler, 2008). Most of the genes related to crime result into negative impacts on the functioning of the neurotransmitter systems. A good example is the gene responsible for sensitivity of dopamine that can raise the desire for arousal a feature of anti-social behavior.
Systematic review is a literature review method that centers on a research question that attempts to process research based information related to that question (Glasziou, 2001). This method is mainly utilized in proof based medicine, but is also applicable in other disciplines. The main objective of systematic reviews is to give in-depth summary of literary works related to a research question. In most instances, systematic reviews use statistical methods that combine the outcomes of the study.
Fig1. Shows our literature meta-analysis framework
Compared with classical review methods, systematic reviews are devoid of bias which can be on the original report, and bias from reviewers. Systematic reviews are specific to issues that are important to patients. They highlight areas where evidence is deficient. In systematic reviews, the best outcome for the patients can be selected. This is not the case in classical reviews where an outcome is selected with the intention of limiting the sample size. Another advantage of systematic reviews is that they can be used to study unusual events by accumulating evidence from all studies. It is very easy to come up with new evidence as compared to traditional forms of review (Glasziou, 2001).
In systematic reviews, a summary of the results is carried out using meta-analysis while in the classical reviews such summaries are uncommon. In classical reviews, sensitivity analysis, studies of subgroups and meta-regression are not conducted while in systematic reviews they are performed to determine if a certain treatment strategy is functional in certain groups of patients. In classical reviews, the description of treatment effects is not clear while in systematic reviews the effects are clearly outlined to determine the risks associated with a form of treatment and reduction of the risks, which are critical in determining clinical decisions (Glasziou, 2001).
Searches were conducted on PsycINFO, Scopus, Medline, PsycBooks, Web science and Psychiatry online for the period covering the publication of Crime and Personality in 1965 by Eysenck to the year 2012. Due to the large content of literature concerning personality traits and their relationship to crime, a specific criteria was used to determine the suitability of the papers for inclusion in the review. Searches were conducted on all the databases for peer reviewed, published, or those papers still with the publisher that contained research results and utilized the term trait theory, Eysenck theory, anti-social behavior and criminality, and personality. These terms were either used as titles or keywords.
Papers that dwelled on personality and crime were selected for the review, and the abstracts of the selected papers were read by a single reviewer. References of the selected articles were selected by manually means to determine the existence of relevant information, and should fall within the specified time line of publication. There were no constraints in the methods applied since statistical synthesis was not included in the review. Qualitative and quantitative studies were therefore part of the study. In the instance of the occurrence of uncertainty in inclusion classification, abstracts were reviewed by a second person, and in most cases agreement was reached by discussion. If uncertainty prevailed, such papers were included in the final selection. The study traits and outcomes of the included papers were outlined by one reviewer and then checked by a second one.
Results and discussion
The database search came up with 31000 papers with related information to the research question. These were the identified and screened materials in the data base. 23000 sources were excluded based on thematic irrelevancies and could not be fit for this study. They were rejected and excluded in our source materials. At the same time, 36 sources were rejected based on their narrow scope in the topic under discussion. Only 36 materials could be fully be accessed and retrieved with relevancy to the topic, however, due to several limitations further exclusions were performed on the materials. 600 of the resources were excluded on the grounds of irrelevancy on design. Some information materials lacked strong background design and were as a result excluded.
Further 259 were rejected on failure in consistency in information. Of these, 211 lacked proper background, 24 had doubtable outcome, 20 failed in delivering the traits needed, while 20 were merely duplicates. 6 materials were excluded since they were expert contact materials, reference list materials and included publications only. These gave very little information for our work, hence they were considered inefficient.56 materials though had all the information we needed could not be used as they were written in languages inappropriate for our audience and they were left on the grounds of inappropriate languages. Finally other materials were excluded based on lack of information specificity and flow in information. The number which was at the end available for research excluding publications was 14 materials for this paper.
It should be understood that to arrive at these results, our elimination procedure was manually based. Use of computers was found to be backsliding since getting duplicates and irrelevant materials could not be ascertained. Computers as well, in the early stages could not provide clarity for materials in varied languages. The finals resources we rated perfect for the study and provided our findings with the most possible accurate information in our study. Since our study was based on literature material, some indifferences may occur from our results and conclusions , however, with very minimal margins.
Traits approach to personality
Of the reviewed articles, five of them examined the role of biological factors in determining criminal behavior. By so doing, they supported Eysenck’s theory of criminality which postulates that the tendency of an individual to engage in criminal activities lies in their genetic makeup. The articles showed almost similarity in drawing their supportive points. Two of the articles analyzed the association of the environment to behavioral traits that contribute to criminality. All of the articles agreed that the combination of some neurophysiological characteristics and the nature of the surroundings predispose an individual to certain criminal activities and they will have no control over their actions. This explains the existence of different types of criminal activities.
The reviews of the above literature show that there is a likelihood that genetics has a role to play in the personality of criminals. Although more studies are needed to clarify this assumption, theories like the Eysenck theory postulate that genetic makeup and the environment are influential in determining the tendency of engaging in criminal activities. One of the reasons that support this theory is the existence of various types of criminals. This is due to the uniqueness of the biological composition and different environments that contribute to this variance.
Further research on this theory can offer the key to the management of criminals because it will illustrate the characteristics that are related to crime at a younger age, therefore appropriate measures will be undertaken to control them before they reach adulthood. All in all, researchers must come up with an in-depth understanding of criminal behavior to facilitate its management.
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