Analysis of the relation between intelligence and criminal behavior

Introduction: One of the cognitive aspects of personality is intelligence. A large number of previous studies have shown that the intelligence within the criminal population is decreased, particularly in its verbal aspect. The aim of this study is to determine whether there is a link between intelligence and criminal behavior and how it is manifested. Methods: The research involved criminal inmates of the Correctional institutes of Republic of Srpska and Court Department of Psychiatry Clinic Sokolac who committed homicide and various non-homicide acts. The test group consisted of 60 inmates who have committed homicide (homicide offenders) and a control group of 60 inmates who did not commit homicide (non-homicide offenders). The study was controlled, transverse or cross-sectional study. Results: Average intelligence of inmates (homicidal and non-homicidal) was IQ 95.7. Intelligence of homicide inmates was IQ 97.4 and non-homicide IQ 94.09. Intelligence coeffi cients for non-homicide inmate subgroups were as follows subgroup consisting of robbery offenders (IQ 96.9), subgroup consisting of theft perpetrators (IQ 93.83), subgroups consisting of other criminal offenders (IQ 92.8). Verbal intellectual ability – IQw of homicide inmates was 91.22, and 91.10 IQw of non-homicide inmates. Intellectual abilities in nonverbal or manipulative part were average, but they were higher in homicide inmates group (IQm 103.65) than in the group of non-homicide inmates (IQm 97.08). Conclusion: Average intelligence of investigated inmates (homicide and non-homicide) is lower than in the general population and corresponds to low average. Verbal part of intelligence is lowered while nonverbal part is within the average range. © 2012 All rights reserved


Introduction
An individual has all the characteristics of a person, its uniqueness and individuality, which makes it diff erent from all the others.Personality is formed in the interaction of heredity and external environment.By the word of HJ Eysenck: "Personality is more or less solid organization of character, temperament, intellect and physical constitution" (1)(2)(3).Intelligence in its essence is constitutionally and genetically defi ned capacity, but it is also to a large extent shaped by the envi-ronment (by upbringing and education and possibility of fl ow of information).It is defi ned as a complex ability to assimilate factual knowledge; to respond to logical and to manipulate concepts, to translate literally to abstract, to cope meaningfully and clearly with problems and priorities assessed and valued as important in certain situation, the ability to solve new problems and mentally adapt to new roles.It is defi ned as the capacity for learning and usage of things learned (3,5,6).NMR studies associate the brain of violent criminals diagnosed with psychopathy, their emotional and cognitive defi cits, with a reduced orbitofrontal areas of the brain as well as abnormalities of amygdala nuclei (4).Numerous studies prove that the intelligence of de-linquents is lower in comparison with the general population.We can even see the diff erences between groups of delinquents.Lowest intelligence is associated with groups of violent off enders.Delinquents achieve lowest score in the area of verbal ability and abstract reasoning, while in terms of other cognitive abilities they don't fall behind in comparison to the general population (5)(6)(7)(8)(9)(10)(11). Sample of 370 inmates convicted for non-sexual violent off enses proved that convicts with no diagnosis of psychopathy have higher overall coeffi cient of intelligence, as well as in its verbal part, from those having this diagnosis.Th e study proves that non psychopaths start much later with criminal activities (12).Linkage of lower intelligence with criminal behavior is explained in various ways: low intelligence leads to poor school performance and those who fail in school are less likely to succeed in life and will probably resort to delinquent behavior.School failure, the frustration that causes uncomfortable feelings lead to a drop in self-esteem, and it may already be suffi cient cause for delinquent behavior apart in drop in verbal skills which are important for communication that can be used to solve many problems.People of low verbal ability are having hard time coping with various social situations which at some point can be the impetus for delinquent behavior; persons of low verbal abilities fi nd it hard to adopt the moral standards of society (6)(7)(8)(9)(10)(11)(12)(13).We compared the samples of juvenile delinquents and non-delinquents and found that the delinquents had pronounced impairment of cognitive abilities (the lag in verbal abilities) than non-delinquents.We also showed that delinquents present conative disorders of depressive and obsessive type (6)(7)(8)(9)(10)(11)(12)(13).Impulsivity is one of the main reasons behind committing crimes by mentally retarded persons as well as their suggestibility paired with insufficient understanding of moral rules and the possibility of learning from experience.Increased suggestibility of mentally retarded people, in addition to committing criminal acts, has a profound eff ect on making false confessions.Th e most common forms of criminal off enses among mentally retarded persons were property crimes (theft , robbery and burglary), sexual off enses, violent off enses (murder and causing grievous bodily harm) and intentional arson (6)(7)(8)(9)(10)(11)(12)(13).
Dementia can be associated with delinquent behavior in terms of harmful behaviors of demented people to himself and to others.As a result of severe memory impairment and confusion demented people can cause fi res, and as a result of delusional ideas of persecution and emotional instability they can hurt or even kill another person (6)(7)(8)(9)(10)(11)(12)(13).Th e aim of this study is to determine whether there is a correlation between intelligence and criminal behavior and how these linkages are manifested.

Methods
Research involved the inmates of correctional institutes from the Republic of Srpska (KPZ "Tunjice") Banja Luka, Prison "Kula" of Eastern Sarajevo, (Foca prison) and the Court Department of the Psychiatry Clinic Sokolac.A total of 105 inmates who had committed suicide and 100 resident perpetrators of non-homicide acts have been examined.15 inmates who have been convicted on the issue of war crimes (war criminals were not covered by our study) were excluded from the group as well as 30 inmates for incompletely and incorrectly completion of psychological tests.Exclusion from the group of non-homicidal inmates was performed due to excessive link between criminal acts with war situations (12 inmates) as well as because of incomplete and / or incorrectly completed psychological tests (28 inmates).Aft er these exclusions, test group was formed consisting of homicide persons (murderers)-60 inmates and a control group of non-homicide persons(non murderers), also 60 inmates.Th e control group was formed from the perpetrators of robbery (N = 22), theft (N = 18) and other off enses (N = 20).In the subgroup of non-homicide perpetrators of other crimes were the perpetrators of illegal production and traffi c of drugs (N = 7), endangering public transportation (N = 4), rape (N = 3), tax evasion (N = 2), illicit production and trade of weapons and explosive devices (N = 1), counterfeiting (N = 1), sexual child abuse (N = 1) and fraud (N = 1).Subjects in the test group and the control group approached to the research on a voluntary basis.Th e study was controlled, transverse (cross-sectional study).Intelligence tests, verbal and nonverbal, were used for the purposes of exploration of problem as well as exploration of objectives of study.Verbal intelligence test was informative test consisting of twenty questions on which inmates answered textually.Questions were tailored to various levels of education and in the domain of the various scientifi c fi elds.Nonverbal or manipulative intelligence test was the Revised Beta test consisting of six subtests.Intellectual skills assessed on the basis of these intelligence tests were expressed using intelligence coeffi cients (IQ): 1) IQ 70 and <-defective intelligence 2) IQ 71-79 -low 3) IQ 80-89 -below average 4) IQ 90-109 -average 5) IQ 110 -119 -above average 6) IQ 120 -128 -high 7) IQ of 129 -> -very high Statistical analysis characteristics observed in the study were subjected to descriptive statistical methods -measures of central tendency (mean, median, minimum, maximum, measures of variability (standard deviation) and relative numbers as indicators of the structure.In order to make relevant conclusions, notable differences between groups were analyzed by param-eter (Student's t-test) and non parameter (Fisher, Pearson Chi-Square -chi-square test, Mann-Whitney U test, Kolmogorov-Smirnov Z-test) statistical methods.Using statistical methods (ANOVA -analysis of variance and LSD -test least significant diff erence), diff erences between the groups and subgroups of homicide and non-homicide inmates were analyzed (subgroup perpetrators of robbery, theft perpetrators subgroup and subgroup of perpetrators of other crimes).Results of statistical analysis were presented in tabular form.Poor academic performance and low educational level and thus the weaker verbal abilities have its roots in asocial-psychopathic features that are prominent in the group of homicide inmates, which has been proven in research.Better performance on nonverbal or manipulative part probably provides skill in some types of delinquency (5)(6)(7)(8)(9)(10)(11)(12)(13).

Conclusion
Average intelligence of investigated inmates (homicide and non-homicide) is lower than in the general population.Homicide inmate's intelligence was shown to be slightly greater than nonhomicide group.Intellectual skills were average in verbal or manipulative part, but were more pronounced in the homicide group than in the nonhomicide group.Verbal intellectual abilities were lower than average for the general population and they were in lower border range in both groups.

Competing interests
Authors declare no competing interests.
of statistical analysis of the results of psychological processing of nonverbal and verbal intelligence tests of experimental and control groups is presented.Intergroup diff erences test(t-test) shows that there is a statistically signifi cant diff erence between the groups on nonverbal intelligence tests T 2, a highly statistically signifi cant diff erence in non verbal test T 4, and a highly statistically signifi cant diff erence in the overall non-verbal (manipulative) intelligence test-nonverbal intelligence coeffi cient of homicide inmates (IQm 103.65) and non non-homicide (IQm 97.8).

TABLE 1 .
NonAnalysis of variance showed a statistically significant diff erence between the groups in T 3, T 5 and T6 nonverbal intelligence tests, as well as the overall IQm (nonverbal or manipulative intelligence -verbal tests (T 1 -T 6), verbal intelligence tests -descriptive statistics and intergroup differences test (T-test).N -number of respondents, the Mean -the mean value, t -value of T-test, df -degree of freedom, P -probability, Mean diff -differences in mean values.

TABLE 2 .
ANOVA (analysis of variance) -statistical analysis of intergroup, intragroup and total variability in verbal and nonverbal intelligence tests.

TABLE 3 .
. Structure IQw (verbal intelligence coeffi cient) for each group of inmates with regard to the type of crime coeffi cient), as well as high statistically signifi cant diff erence in the T 2 nonverbal intelligence test.Th e least signifi cant diff erence test (LSD test).

TABLE 4 .
Testing the signifi cance of difference in coeffi cients of verbal intelligence (IQw) between groups of inmates with regard to the type of crime by means of factorial analysis of varianceranks (Kruskal-Wallis test)

TABLE 5 .
Structure of IQm (non-verbal or manipulative intelligence coeffi cient) for each group of inmates with regard to the type of crime

TABLE 6 .
Testing the IQm signifi cance of difference between all groups and sub-groups of inmates using factorial analysis of variance ranks (Kruskal-Wallis test)

TABLE 7 .
Testing the signifi cance of IQm differences between subgroups of non-homicide inmates considering the type of crime committed using Kruskal-Wallis test.According to the literature, lower verbal intellectual abilities may be due to lower levels of education, but they may exist before going to school and be a result of neurophysiologic defi cit.Reduced intel-lectual ability, particularly decreased verbal intelligence factor, can have a signifi cant impact on the development of delinquent properties of inmates.Lower intelligence lead to poor school performance and people who fail in school are less likely to succeed in life so they easily resort to delinquent behavior.Failure in school is a strong frustration that can lead to the occurrence of aggression and criminal behavior.People with reduced verbal communication skills are weak and disoriented in various social situations, which can lead to the development of delinquent behavior.People with low verbal abilities fi nd it hard to adopt the norms of morality and recourse to asocial or even delinquent actions.Verbal skills are important in the control of behavior, that is, the ability to connect potential reactions with potential consequences.