Abstract
Introduction: Although there now has been a decrease in crime, violence and homicide remains to be a persisting and serious problem in many parts of the world. To successfully intervene or effectively treat juveniles to prevent them from chronic delinquency (i.e. persist on violence into their young adulthood) much should be known about the risk factors. This review aims to list major risk factors for serious violent delinquency, specifically in young adult men.
Method: There was searched in databases for peer-reviewed articles that examined the development of violence in young adults, preferably men.
Results: 11 articles where concluded in this review, almost all where longitudinal cohort studies. most results focused on social and environment factors, whereas only 3 studies where neurobiological Results reported main risk factors on social domain including: environmental (bad neighborhood, low SES, family factors), peer delinquency and substance use. On the cognitive domain main risk factors where: low executive functions, verbal IQ and impulsivity. Neurobiological factors where: the L-MAOA allele and lower amygdala volume.
Conclusion: Although there is predictive power of risk factors from the social/environmental domain, finding out which neurobiological factors (in interaction with social and other factors) seems to be the next step in constructing the development of violence and thereby homicide.
Why young adult men
become violent.
A review of major risk factors.
Sophie Reemst2515660 Medicin, Vumc June 2016
Carmen Paalman, forensic psychiatry
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Introduction
Recently, June 12th 2016, one man caused a mass shooting killing 50 people at once. To prevent a person from committing terrible actions like this, sometimes even done by at first sight normal citizens, it is crucial to know which factors (might) could have predicted this man to commit homicide. If you see how it is still a big impact on everyone’s lives even following the actual news it is no wonder violence and delinquency has become an interesting field of studying the last decade. Although there now has been a decrease in crime, violence and homicide remains to be a persisting and serious problem in many parts of the world. In the USA alone investigation showed that in 2008, 7307 young people between the ages of 15 and 29 were victims of homicide giving an average of 20 each day (Loeber & Farrington, 2011). When crime reached its highest point in the USA in the early nineties (Loeber et al., 2005) there still was a lot unknown about the development of this kind of behavior in juveniles. Around the same time (1987) they started de PYS: Pittsburg Youth study. A longitudinal study consisting of repeated assessments of 3 cohorts of boys. The aim was to investigate delinquency causes in those guys from childhood to early adulthood. In the mean time a lot of new findings came from this study, which will for that reason and the specific sample also be the foundation for this review. Results important for this review will be their examination of the predictors of homicide, first by predicting violence and secondly by predicting homicide among the violent boys. They explored that homicide in juvenile delinquency needs a necessary precursor: violence (Loeber & Ahonen, 2013). Because it is thought to be the most rewarding to intervene on a young age (Stams, van der Put, & Dekovic, 2012), a lot has been written about risk factors for violence and delinquency in early childhood and adolescents. There has also been a lot of research for intervention, recidivism and lately the field of promoting factors or the reason for desisting is a new area of interest (Loeber & Pardini 2007). As seen by the age-crime curve, first described by Farrington (1986), crime increases during childhood into late adolescence where it decreases again into early adulthood. This curve is somewhat similar to the curve of violence except the last one peaks a bit later (Loeber & Farrington, 2011). Still violence and delinquency remains, even in adult men. Either
those man had a late onset or they persist their behavior into their young adulthood, Fairchild, Van Goozen, Calder, & Goodyer (2013) stated that adolescence delinquency not necessarily needs to stop in early adulthood. Research on juvenile delinquency has shown that a small group of persistent offenders is responsible for a disproportionate amount of crimes (Moffitt, 2006). To successfully intervene or effectively treat juveniles to prevent them from chronic delinquency (i.e. persist on violence into their young adulthood) much should be known about the risk factors for this specific group. This review aims to answer the following question: what are the major risk factors for serious violent delinquency in men during young adulthood?
As risk factors can be in any domain and violence is a widely concept where lots of factors can be considered it is useful to specify the main elements of this question. To answer this question, first there has to
be a clear definition of violence and delinquency. In public health studies violence is defined as the ‘threatened of actual use of physical force against a person or a group that either results or is likely to result in injury of death’ (Dahlberg & Potter, 2001). Delinquency is to commit a crime and can be divided in to non-violent or violent delinquency.
Thus this review is not as much about aggressive behavior but moreover the serious act of violence, committing a crime, which in the most severe form contains homicide. The pathway of doing so is complex and consists of several risk factors. Risk factors are all the factors contributing to the development of violence. Violence is known as a build up of several factors which together causes the act of violence, or in case of homicide as Heide (1999) suggested: the probability of individuals committing homicide is enhanced by their exposure to an accumulation of different risk factors. An heuristic model based on empirical studies has been made which shows how social, individual, economic, environmental and neurobiological factors influence the development of violence, see Figure 1. Literature also shows classification in the development of serious delinquency, for example Loeber et al (2008) suggested 5 domains of risk factors: individual, family, peers, school and neighborhood.
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Figure 1: Relationships between elements of
neurobiological and social/contextual factors that influence the development of violence. (Loeber & Pardini, 2008)
This review aims to list major risk factors for serious violent delinquency, specifically in young adult men. As discussed above a lot of factors can contribute, and this review will not be able to give a detailed list of all factors, the focus will be on the main factors given by previous literature.
Method
As this is a literature review, studies were selected by several criteria. First, they had to examine the development of violence, preferably in young adult men. Excluded where studies that solely examined one type of offending (e.g. sexual, partner, parent) or studies whose samples only consisted of psychiatric patients, or children. This because they would not be representative for all violent and delinquent young adult men. Selection was made as well on type of study, for this review results of prospective longitudinal studies where used. Included where studies with all kind of ways to examine the development of violence including several domains (e.g. social, cognitive, neurobiological). As many studies examined children or adolescents, studies that reported on late adolescence (untill age 19/20) where added, as well as studies that differentiated between man and women. There was searched for peer-reviewed articles and book chapters in 2 databases: Web of Science and PsychInfo. The search strategy was as followed: a combination of risk* OR develop* OR predict* OR precursor* OR trend* OR association* AND young adult* OR early adult* AND violen* AND male OR men OR boy*.
Introduction Results: Conclusion:
This search gave 641 results in psychINfO; if methodology, as above described, was added there where 106 results. In Webofscience there where 5688. After adding TI (title) for all the descriptions of ‘risk’ (of risk* OR develop* OR predict* OR precursor* OR trend* OR association* and a NOT factor (sex, partner & victim) 476 studies remained. All studies were screened by reading title, abstracts and if necessary full articles. Focusing on inclusion and exclusion criteria resulted in a final of 8 studies. By reading reference lists 3 additional studies where found to contribute to the results review. At the end 11 studies where suitable to use.
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Results
Flowchart
Table 1
Article Study Sample Method Result
Loeber et al (2005). The prediction of violence and homicide in young men. PYS. 1517 high-risk boys. Mean age: 18.9 (range 15-26).
Prospective longitudinal study
11 out of 50 significant risk factors predicted violence the most: low SES, family on welfare, bad neighborhood, truancy, low school motivation, high parental stress, onset of delinquency before 10 years of age, cruel to people, depressed mood, physical aggression, and callous/unemotional behavior Loeber et al (2007). Do cognitive, physiological, and psychosocial risk and promotive factors predict desitance from delinquency in males. PYS. 1517 high-risk boys. Mean age: 18.9 (range 15-26).
Prospective longitudinal study
6 out of 19 significant risk factors where most associated with violent delinquency: high peer delinquency, high tobacco use, high alcohol use, high drug selling, high interpersonal callousness, high truancy. Search results = 582
Digital databases PsychINFO: 106 Web of Science: 476
Studies screened for detailed screening: 39
Selection based on full article n= 8
Included in review: n=11
Excluded based on title, abstract and duplication: n = 543
-‐ Outcome was not violence or violent delinquency
-‐ Sample didn’t include young adults (mean age
between 19-24)
-‐ Sample was not representable for the average young
adult men (e.g. only one race, only psychiatric patients)
-‐ Article was written before 2005
-‐ Not a longitudinal cohort study
-‐ Double results
Included by screening references: n= 3
Excluded based on exclusion criteria above and effect (effect mate could not be considered as a major risk factor): n=31
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R.J. Zagar & W.M. Grove (2010). Violence risk appraisal of male and female youth, adult, and individuals. 1127 youth, 1595 adults and 2722 individuals. 85.3% of adults where men. Prospective longitudinal studyFor adults there where 11 significant main predictors for violence, in order of
importance: executive function, prior court contact, men, alcohol & substance abuse, violent family, unemployment,
underachievement, hyperactivity, SES and illnesses.
J.J. Sijtsema et al. (2015). The structured assessment of
violence risk in youth in lalrge community sample of young adult males and females. The TRAILS study. TRAILS. 963 men and women. Mean age = 19.1 Prospective longitudinal study
Peer delinquency, low empathy/remorse, history of (non-)violent offending, stress and poor coping, and
risk-taking/impulsivity scored significantly in men. History of offending was associated with violence, social support was
negatively associated with violence.
Bernat. D.H. et al (2012) Risk and direct protective factors for youth violence: results from the national longitudinal study of adolescent health. 1073 young men/female adults 18-20 years. 87 on reporting violence. Longitudinal cohort.
Peer delinquency was associated with violence.
(Barker et al., 2007) Developmental trajectories of male physical violence and theft. Relations to neurocognitive performance. HHDP: 698 men. Assessments at at 12, 15, 18, 21 and 24.5 years. A prospective cohort-sequential longitudinal study
Frequently physical violence was associated with lower cognitive performance: verbal IQ & executive functions .
Loeber et al. (2008). Violence and Serious Theft: Development and Prediction from Childhood to Adulthood.
Substance use, drug selling, gang membership, gun carrying.
PYS. 1517 high-risk boys. Using the oldest cohort, age range 20-25 years. Prospective longitudinal study
Alcohol use in early adolescence significantly doubled the risk of later violence in young adulthood, late adolescence dit not. Early adolescence frequent marijuana smokers significantly predicted violence in young adulthood, late adolescence smokers did not. Gang members and gun carrying during early adolescence had a risk of 3-5 times of later violence, even with controls for current violence. Pardini, D.A. et al (2014). Lower Amygdala Volume in Men is associated with childhood aggression, early psychopathic traits, and future violence.
PYS. 56 high-risk boys. Neuroimaging at Age 26. Prospective longitudinal study
Lower amygdala volume was associated with an increased risk for engaging in future aggression and violence in adulthood.
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Stetler. D.A. et al.(2014). Association of low-activity MAOA allelic variants with violent crime in incarcerated offenders. 89 Caucasian and African-American men. 49 violent and 40 non violent controls. Mean age = 28 Case-control study.
Charges of violent crime were
significantly more in carriers of L-MAOA alleles, especially in Caucasian men.
Hexuan. L et al (2015). Gene by social-environment interaction for youth delinquency and violence: thirty nine-aggression related genes. Add Health 1425 men and women. Mean age = 22. Longitudinal
cohort. Adolescents who where less attached to parents and school, loosely disciplined by parents and school authorities, lived in neighborhoods with high unemployment and low income rates had more genetic risk for violence. Those where significant interactions between aggression-related gene variants and environment.
Sourander. A. et al (2006) Childhood predictors of male criminality: a prospective population-based follow-up study from age 8 to late adolescence. 2713 Finnish boys ‘from a boy to a men study’. Age = 16-20. A follow up study.
Strongest predictive associations with later violence where: living in a broken home, bullying, low parent educational level, hyperactivity and conduct problems.
In this review results where included from 11 articles written between 2005 till 2015. Almost all where longitudinal/ follow up except for one, which was a case-control study. Different longitudinal samples where used: four times the Pittsburg Youth Study, the Dutch sample TRAILS, the Rutgers Health and Human Development Project (HHDP), the ‘From a Boy to a Man’ study, the time the National Longitudinal Study of Adolescent Health (Add health), the rest where samples not specifically belonging to a study. Sample sizes where between 56 and 2713. While the PYS, HHDP, ‘from a a boy to a men’ study and the study of Stetler. D.A. et al. (2014) consisted of only men the rest of the samples where both male and female. When possible, the results given in table 1 where are adjusted for men, as well as adjustment for young adults when there were more groups of different mean ages. In terms of different aspects of approach to the risk factors of violence, most results focused on social and
environment factors, whereas only 3 studies where neurobiological.
Social/environment
Five studies included many risk factors of different domains whereas one specifically focused on neurocognitive factors, one specifically on substance use, drug selling, gang membership and gun carrying and one study searched for interactions between violence related gene variants and social-environment. Six studies reported environment factors in their major risk factors, including: neighborhood, low SES and family factors. Four studies reported previous violence/aggression in childhood as major risk factor. Peer delinquency and substance use was reported in three studies, as well as callousness. three studies reported on executive functions (e.g. coping, motivation, impulsivity) as major risk factors. Truancy, hyperactivity & conduct disorder where both reported two times. One
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study specifically associated previous bullying with violence. Also one study found gang membership & gun carrying and drug dealing as a significantly risk factor.Neurobiological
There where three studies reporting on neurobiological factors for violence, all on different aspects. One was a case-control study with violent en non-violent males, this study concluded L-MAOA was associated with violent crimes, especially in Caucasian men. One was a prospective longitudinal cohort study consisting of only violent boys concluding that a lower amygdala volume was associated with future violence. There where neurocognitive findings in one study: low verbal IQ & executive functions where risk factors for violence in young adult men.
Discussion
As expected different factors where found contributing to development of violence in young adult men. Main risk factors on social domain included: environmental (bad neighborhood, low SES, family factors), peer delinquency and substance use. On the cognitive domain main risk factors where: low executive functions, verbal IQ and impulsivity. Neurobiological factors where: the L-MAOA allele and lower amygdala volume. Those neurobiological factors are part of the factors considered by Loeber et al. (2015) when they discussed the influence of biological factors on within-individual change. One study showed significant interactions between aggression-related gene variants and environment contributing to having more genetic risk for violence. This is an important finding, previous literature showed that the sum of individual risk factors results in less of a risk then the risk caused by an interaction between genetic and environmental factors, this one is far higher (Taylor & Kim-Cohen, 2007). Almost half of the studies concluded that previous violent behavior in childhood or adolescence was a precursor for violence in young adulthood. Loeber et al. (2008) showed that 93.9% of the homicide young adult men were violent before committing homicide and concluded that violence was, almost, a necessary precursor of homicide which was confirmed again in their later study to predict homicide offenders and their victims (Loeber & Ahonen, 2013).To
reduce the amount of homicides is it thus crucial to intervene appropriately in violence. Therefore, still more research is needed to construct violence as a developmental cascade which lead to violence.
Limitations of this study where the small amount of articles reviewed. As this is a review for the main risk factors of violence, preferably a meta-analytic review with more studies included would fit best to answer this question. Besides, 4 articles which where used for results shared the same study sample, therefore conclusions might not be generalizable for the main population. Main criticism must be the fact that the articles that included neurobiological factors only reviewed one risk factor (amygdala volume or L-MAOA alleles) for the outcome violence. In addition, the spreading of articles between social/neurobiological was not even, the minority was focused on neurobiological factors. However, this might be a reflection of the actual status of literature about violence. To refer to the heuristic model given in the introduction, the direct influence of social, individual, economic and environmental factors on aggression and violence has been the main focus in studies. Whereas the pathway of genetic, social and other factors, in their interaction, contributing to the changes in neurobiological function and structure is still underexposed. Knowledge of these factors might, next to social risk factors, contribute to the fact that there are individual differences in violence over time. Those differences of minor or major forms of violence, early- or late-onset, desisting or persisting. There is still little agreement and a lack of information on which factors are most important for understanding the development of violence. Although there is predictive power of risk factors from the social/environmental domain, filling the gap, finding out which neurobiological factors (in interaction with social and other factors) seems to be the next step in constructing the development of violence and thereby homicide.
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