The Psychology underpinning “Knife Crime Phenomena”

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The Psychology underpinning “Knife Crime Phenomena”

A British Psychological Society Parliamentary Office Publication

  • Many young people carry knives not with the deliberate intention to harm, but to protect themselves or to gain respect from peers. It is important to decrease fear of crime and give young people alternative strategies to build self-esteem.
  • Although it is not possible to predict whether and when an individual will commit a violent crime, research into the psychology of violent behaviour has uncovered those individual and social factors that increase the likelihood of a violent act.
  • “Norms of behaviour” are acquired through social learning from family or peers. These norms can lead to automatic behaviour choices: when aggressed, retaliation is the only response that comes to mind.
  • Adolescence, a period of increased sensitivity to peer pressure, heightened interest in risk taking and decreased sensitivity to punishment, adds to the risk of getting involved in violent conflicts.
  • To work on the adolescent brain, deterrent and corrective measures should be built on positive feedback for good behaviour instead of negative feedback for bad behaviour.
  • Certainty of punishment and not the harshness of punishment deters young people from crime.
  • To decrease recidivism custodial punishment must be accompanied by appropriate, long term, psychological and social interventions. It is possible to change a young person’s social environment, or give them the cognitive tools to diminish the impact of a negative social environment.
  • To increase efficiency all interventions should be designed based on scientific theories and evidence. Where possible, their impact should be evaluated using golden-standard statistical methods (i.e. randomized controlled trials). 4 Vivid stories of young people stabbing each other and of pupils bringing knives into school have attracted the attention of the media and of central policy makers in the recent past. Statistics released by hospital emergency rooms suggest that ‘youth knife crime’ reflects more than just a media phenomenon or a political catch phrase. The number of hospital stabbing admissions where the victims are under 18 years of age has doubled in the past five years [1]. In response to such figures a variety of measures have been initiated, aimed at tackling the emerging ‘knife crime’ and ‘knife culture’, seemingly without first acquiring a comprehensive understanding of the phenomenon. Such measures include the introduction of metal detectors in schools, frequent ‘Stop and Search’ actions, and longer maximum sentences for possessing a bladed instrument (i.e. knife). This briefing has been prompted by the belief that Psychology (in particular its specialist areas of developmental, clinical, educational, and forensic ) is crucial to the understanding of the complex social phenomenon hidden under the ‘knife crime’ umbrella. Three important aspects of the ‘knife crime’ phenomenon have been identified where the science of psychology can bring answers and solutions. We start by exploring the motivations behind knife carrying by young people. Evidence suggests that an intention to harm is only one of these motivations. Secondly, we consider individual factors linked with interpersonal violence in adolescents: e.g. peer and family influences, personal traits, intoxication. Finally, we will turn to the research on risk perception to show why the perceived likelihood of arrest and not harsher policy deters young people from violence, and why fear of crime is driven by the perceived likelihood of victimisation and not by actual crime rates. The aim is not only to review the scientific evidence available, but also to consider the potential effectiveness of measures taken to address knife crime and importantly to suggest potential alternative interventions which are driven by BPS long tradition of psychological research and practice.

5 1. Knife carrying Based on the assumption that knife carrying leads to the commission of a violent crime, the sentencing options for being in possession of a bladed article have been increased from a maximum of two years to a maximum of four years imprisonment. However, recent UK surveys, and previous psychological research on the motivations behind weapon carrying suggest that intending to threaten or harm is only one of the reasons, other significant motivations being personal protection, or protecting family and friends, which may overcome the fear of imprisonment. Defensive vs. offensive weapon-carrying Many young people in UK, but also in other countries (i.e. Australia), state that they carry weapons to protect themselves from physical attack or being robbed and not to harm [2]. Many of these young people have been victims of violence, have witnessed it or have been threatened with knives/dangerous implements in the past. Others decide to arm themselves only because they believe that other people in the school or local neighbourhood carry guns or knives [3, 4]. It is well known that knife carrying is more frequent in young people excluded from school and involved in gang activities [5, 6]. These people are often successively victims and then perpetrators of violence [7] and therefore, may have difficulty distinguishing between defensive and offensive knife carrying. Both motivations could have been true at different moments in time and one could easily lead to the other (“protecting” oneself may involve threatening or harming). Fear of victimization can lead to increased knife-carrying because experiencing prolonged fear, as a result of repeated verbal or physical aggression, can lead to depression, or anxiety [8]. This is particularly true of younger people, in the 10 to 15 age group who, among adolescents, express the highest fear of victimization [6]. This is also the age group who may be less sensitive to the consequences of risky behaviour (see Box 1) Metal detectors, after-school police patrols and giving search powers to teachers are designed to increase safety on school grounds. Although teachers welcome most of these 6 measures [9], no research has been conducted to date in UK to estimate whether the perceived school safety has indeed increased following their introduction. An evaluation of the effects of ‘zero tolerance’ policies in US schools, published by the American Psychological Society, found that they did not affect parents’ perceptions of levels of safety, and found evidence for an inverse relationship between school expulsion and school academic achievement [10]. Factors proposed to explain the failure of these measures included: • schools were already a relatively safe place, as opposed to the street; • adopting ‘zero tolerance’ policies signalled to pupils and parents that there was an imminent danger, thus leading to increased fear and its detrimental effects; and, • school expulsion for knife carrying may be used as a strategy to skip school. Popularity amongst peers Another reason often given for carrying knifes is the need to be accepted and “respected” by peers [4,5,6]. Peer socialization becomes crucial in late adolescence (see Box 1). The consequences of acquiring popularity amongst peers can go from accepting certain dress codes, to substance use and delinquency, (e.g. carrying a weapon) [11]. Whether young people will decide to carry a weapon, excel in sports or an academic discipline to increase their status amongst peers, depends on the social mores which prevail in the community at large or within their families or peers (see Box 2). Joanna Barlas of Glasgow Caledonian University asked British teenagers what they thought about carrying a weapon. Surprisingly, it was those not carrying weapons that mostly believed weapons bring respect, power, or make them look ‘cool’ [2]. Thus, although the decision to arm oneself may initially be driven by the desire to gain status, these perceptions change once one experiences the pros and cons of being armed. Violence is only one of the reasons young people carry knives. To diminish knife carrying, policy measures have to address all the underlying motivational factors. 7 Box 1 : The adolescent brain and antisocial behaviour The age–crime curve for property crime and violence is a universally observed curve showing that the prevalence of offending is low in late childhood and early adolescence, peaks in middle to late adolescence and decreases subsequently [13]. Longitudinal studies have shown that this adolescence-limited profile accounts for a quarter of those involved in violent offences [14, 15]. The increase in offending at adolescence is paralleled by an increase in other risky behaviours like smoking and substance use [16]. We know now that the increase in risktaking behaviour is not the result of teenagers not being able to perceive risk but of difficulties they have with decision making, especially under challenging emotional or social conditions [17]. Adolescents are biased towards choosing immediate rewards, even if these rewards lead to a delayed punishment [17]. Adolescents that show the strongest bias towards immediate gratification also show greater involvement with alcohol, marijuana and they underperform academically [18]. Teenagers are in general more sensitive to rewards than punishment [19]. Thus, strategies that employ positive reinforcement of desired behaviour (e.g. telling them that not giving in to peer pressure is a sign of selfcontrol and praising them for exercising self control) may be more effective than those emphasizing the negative consequences of risky behaviour (e.g. “Carry a knife and the consequences will follow”, Met Police ad). An exception from this rule are social rewards. Both peer acceptance and rejection strongly activate areas of the brain involved in reward recognition [20]. These behavioural characteristics are the potential consequences of changes in brain anatomy and function taking place during adolescence [17]. Brain areas involved in immediate reward seeking and in processing emotional information (e.g. the limbic system) are very active during early adolescence. The increased sensitivity to peers is related to changes in oxytocin release in the brain. This hormone and neurotransmitter also acts within the limbic system and appears to be connected with aspects of affective bonding. In a similar way that biological changes in early adolescence make young people susceptible to join delinquent groups and get involved in risky antisocial behaviour, other biological changes, in late adolescence, will increase self-esteem and decrease the susceptibility to peer influence [17]. Limbic areas are under the control of the pre-frontal cortex, which becomes fully mature only in late adolescence. This area of the brain helps inhibit impulsive behaviour by allowing more information to be taken into account in decision-making (e.g. estimating the probability of being caught, knowledge about punishment severity, alternatives ways of solving conflict). The increase in risk-taking and the susceptibility to peer influence in adolescence is normative, biological driven and a useful process, from an evolutionary psychology perspective. In reaching sexual maturity young people need to venture away from the family environment in search of an appropriate partner and, frequently, compete for this partner with their peers (which implies competing for a certain status) [12]. Despite these generic developmental processes not all adolescents take the anti-social behaviour path. Whether this will happen or not depends on many personal and social factors but also on the opportunities available to satisfy adolescents’ needs for strong sensations;


“Being bored” is the most common reason they give for offending [5]. Diverting adolescents towards behaviours that are not damaging to themselves, and to others, but satisfy their need for immediate positive rewards and strong sensations could contribute to reducing their involvement in anti-social behaviour. 8 2. Knife-mediated violence Only a small proportion of young people are responsible for the majority of violent offences [15], therefore, research has been aimed at finding individual factors that might predispose certain young people to violent behaviour (e.g. cognitive and emotional abilities, the norms of conduct learned from family or peers or the amount and quality of parental supervision). Conversely, because even a persistent offender will not act violently at every encounter it is also important to look at particular situational characteristics such as the effect of alcohol consumption, or the presence of peers on the process of decision making. Risk-factors analysis A widely used approach to understanding, and estimating, the likelihood of violent behaviour is through the assessment of well-established risk and protective factors. These are characteristics that can increase or decrease the chance of engaging in a set of criminal behaviours. Individual characteristics (e.g. temperament, personality features, developmental history), family context (e.g. parental supervision, an antisocial parent), or the social and economic environment (e.g. poor neighbourhoods, the presence of gangs) have repeatedly been highlighted as risk factors [21] This approach is relatively successful in assessing the likelihood of re-offending (e.g. a good predictor for being caught carrying a knife is having already been caught carrying a knife) but this approach is not as accurate for rare offences, like homicide [22] [23]. Recently, there has been an increased interest in identifying early risk factors for delinquency in general and violent behaviour in particular. Identifying at-risk children might facilitate effective interventions even before a child has stepped onto a path towards likely delinquency [23]. Care should be taken that labelling a child as being “at-risk” does not lead to social exclusion, which is in itself a risk factor for anti-social behaviour. One potential approach is to always assess both risk and protective factors and to portray them as “indicators” and not “predictors” of later “good” or “bad” behaviour. 9 Cognitive and Emotional abilities. Violence can be seen ultimately as a decision-making act, where long-term costs (legal sanctions, loss of social support, delayed retaliation) are disregarded for the sake of immediate benefits (emotional satisfaction, monetary gains) [24]. A number of individual characteristics like low self-control, ability to project oneself in the future or low empathy could bias a young person’s decisions towards immediate benefits and against the long-term costs of their actions [13, 25]. When assessed at their place of confinement, away from the highly emotional world of real conflicts, violent offenders did not consistently differ from non-violent offenders in tasks measuring their cognitive abilities [26, 27] nor did juvenile offenders in general differ from nonoffending adolescents [28]. In the latter study all (adolescent) participants were equally biased toward choosing immediate monetary rewards, and did not differ in the way they planned for future events in their life (e.g. buying a car, marriage). Thus, cognitive abilities measured off-line cannot be used as selective predictors of violent behaviour. However, looking at emotional abilities gives different results. Juvenile offenders and those convicted for weapon related violent offences show a higher bias towards sensation seeking and risk-taking [24, 28]. Moreover, aggressive adolescents are less able to recognize emotional expressions and they over interpret other people’s behaviour as hostile [29]. Young offenders show less empathy towards other people’s feelings [25]. Adding the tendency to overattribute hostility to others, to a propensity towards risky behaviour could be enough to prompt conflicts and violent behaviour1 [30]. It is believed that detecting the causes/correlates of problem behaviours early in life would increase the success of interventions. Evidence suggests that a small proportion of schoolaged children show persistent aggressive behaviour and deficits in the processing of emotions. These characteristics are called callous-unemotional traits and appear to be congenital in origin and are highly heritable [31]. Another group of children, which suffered from head traumatisms early in life which have affected the frontal cortex are also less able to control behaviour and to read emotions in others. These difficulties become accentuated in adolescence, when the socioemotional demands increase [32]. Studies in a prison population showed that violent criminals 1 A-level student stabbed to death in bus brawl over a ‘dirty look’, The Evening Standard 28 Dec 2007 10 tend to have a history of untreated repeated childhood brain injury 2 [33]. Thus it seems that there are certain acquired or innate traits that increase the chance of later involvement in anti-social behaviour. Nonetheless it is crucial to remember that only a small proportion of those manifesting callous-emotional traits, or having had traumatic head-injuries in childhood will go on to offend. High-risk neighbourhoods and negative home environments are required as an additional permissive and formative environment for these biological factors to lead to violent behaviour [34]. Multiple factors should always be taken into account before an individual is singled out for intervention. Moral norms and violent behaviour The course of action taken in response to aggression, whether retaliation or walking away, is also dependant on which of these reactions an individual considers appropriate and morally acceptable given the situation. These “moral norms of behaviour” are acquired through social learning from family, community, or peers [35] (see Box 2). These norms can become sufficiently automatic [36] so that when the moment comes to make a decision about how to react to aggression, retaliation is the only alternative which comes to mind. A series of social psychology studies from University of Michigan compared the reaction to insults of undergraduates raised in the South and the North of United States. The southerners, where a ‘culture of honour’ requires that a man restores his diminished reputation (following an insult) by aggressive or violent behaviour, were more upset (as shown by increased levels of cortisol and testosterone) and more likely to react violently [37]. Importantly, just as anti-social moral norms can bias a person towards violence, acquiring pro-social norms diminishes violent behaviour, even in young people who show low self-control and are thus considered “at-risk” [36]. It is, therefore, both challenging and crucial to find the appropriate means to influence young peoples’ moral norms, offering them pro-social alternatives for action in social settings. For example, recent research shows that playing prosocial video games leads to a decrease in aggressive thoughts [39], but see Box 2 for the challenges faced by attempts to change moral norms. 2 (Huw Williams, University of Exeter, evidence brought within the APPG for Acquired Brain Injury) 11 Box 2: Learning behaviour norms The actions an individual will take to diminish their fear, or to gain “respect”, whether carrying a weapon or excelling in sport, will depend on the social norms accepted by the community the individual identifies with, be it peers or family [40, 41]. In a similar way one acquires stereotypes and prejudices about certain social groups, for example racial beliefs, beliefs about allies vs. enemy gangs, or attitudes towards the police [42]. Norms and beliefs do not have to be taught explicitly (e.g. a parent telling their child that carrying a knife is acceptable). Simply overhearing others express these views, witnessing repeated violence, or being a victim of violence is enough to make children perceive weapons and violence as accepted or desirable [40]. Exposure to community violence in general increases children’s aggression [43]. Children raised in families where aggressive retaliation is the norm, over-attribute hostile intent to other people’s behaviour [45]. A study of adolescents admitted to an emergency department for youth assault-related injuries showed that parents and children had very similar attitudes about fighting, and that these attitudes correlated with the child’s aggressive behaviour, and school expulsion [46]. When the influence of parents is diminished, peer groups and their norms take over [47, 48]. Among a sample of Australian young offenders, gun users were more likely to have been introduced to guns by their peers than by older relatives [49]. The role of the media in influencing moral norms and encouraging aggression has been widely debated and it is now agreed that while it is not, on its own, responsible for ‘real-world’ behaviour, the amount of exposure to violent television programmes during childhood, contributes to aggression and violent behaviour [50]. Both short term effects (e.g. imitation of specific behaviours) and long-term effects (e.g. increasing their beliefs that violence is acceptable) have been observed. One of the most important factors seems to be the way violence is portrayed – as a purpose in itself instead as of a means towards a morally accepted goal, only the first scenario leading to increased violent behaviour [51]. Parents, community, peers or the media all require a lengthy and intense period of exposure in order to influence the moral norms that will guide a young persons’ behaviour. Un-learning these norms will also require lengthy exposure to pro-social environments. This poses a challenge to any “quick-fix” attempts to change behavior norms. Parental control Parental supervision is the strongest and the most replicable predictor of offending [23]. Young people often mention “Worry about how parents will react” as a deterrent factor [5]. The emotional nature of the parental supervision is crucial: authoritative parents (warm and affectionate, yet firm in establishing behavioural habits) but not authoritarian parents (that impose a lot of psychological control and are less warm) are more able to successfully control 12 adolescents’ behaviour [52]. Parents that involve their adolescent in joint decision-making and place an emphasis on academic achievement can lead to a decrease in teenagers’ involvement in drug use, and can even influence the type of peer group they join (i.e. delinquent or not) [53]. Peer pressure Young people are far more likely than adults to commit crimes in groups, rather than by themselves [54]1 . This is true of many criminal activities and is explained by the ‘dilution of responsibility’. In addition, the presence of the peer group is a strong catalyst for risky behaviour because it is an opportunity to reaffirm status within the group. Studies have shown that in the presence of peers, adolescents are biased towards making risky decisions [55] and increase their stated willingness to behave in an antisocial fashion [17]. The impact of peers is highest in early adolescence (10 to 14 year olds) but decreases gradually between 14 and 18 years of age, as the ability to self-control develops [56] (see Box 1). Alcohol consumption Alcohol consumption is one of the major risk factors for violent offending [21] and increases the level of both violence or vandalism [57]. Experimentally induced intoxication increases the amount of risk taking and diminishes the perceived impact of negative consequences [58]. The Violence Research Group at Cardiff University has studied the link between alcohol consumption and violence in a large group of teenagers. The frequency of drunkenness was linked to both the frequency of hitting others and of being hit. [59]. This brief review of factors associated with violent behaviour is not exhaustive. Our primary focus was on factors that are frequently discussed in relation to youth violence. Importantly, none of these factors is in itself sufficient or necessary for violence to occur. Most violence is the result of a plethora of coincidental individual, social and contextual factors. To better understand violence and to better tailor preventative policies we should use a cumulative assessment of individual and social risk-factors. 13 3. Risk perception, risk communication and behaviour Understanding risk perception is crucial for understanding ‘knife crime’. One of the expected effects of punishment is deterring people from committing crime. It is widely accepted that harsher punishment does not necessarily lead to a decrease in crime. Whether a young person will commit a crime depends first of all on how likely they believe they are to be punished. Whether a person will take precautions to prevent becoming a victim of crime also depends on how likely they think that it can happen to them. Risk perception and deterrence Contrary to its expected effect, the adoption of harsh punishments does not always lead to a decrease in the levels of criminality. Prolonging sentences does not proportionally decrease the rate of juvenile offences [60]. In Texas, one of the most active death penalty States, there is no correlation between the execution rate and the murder rate. Research on decision-making has shown that for punishment to work (1) punishment has to be certain and (2) it has to be administered immediately after the crime was committed [61]. Home Office data suggests that only about 2 per cent of all offences committed result in a conviction [62]. This makes young people believe that they are unlikely to be caught carrying a knife, therefore diminishing the expected deterrent effect of these measures (see Box 3). Many young people know, from personal or their friends’ experience, that even if caught carrying a knife they can avoid a custodial sentence [7]. Therefore the priority should be on increasing the certainty of punishment , not increasing its harshness. The media has an impact on risk perception (see Box 3). The majority of crime news focuses on the victim, and only for a short period of time after the event. We rarely hear about criminals being caught and punished, their personal characteristics and their motivations. Also, a great emphasis is put on the outcome of sensational, but rare, crimes like murder. All these factors diminish the chance that a potential perpetrator identifies with a prosecuted criminal and perceives the risk level associated with a certain crime.


Arthur Cassidy PhD, C.Psychol