Does Schizophrenia Increase the Risk of Violence: A Literature Review and Public Health Perspective

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1 Does Schizophrenia Increase the Risk of Violence: A Literature Review and Public Health Perspective December, 1992: Jonathan Zito, a young musician, is the victim of an unprovoked attack outside Finsbury Park Station. He is stabbed repeatedly in the face with a screwdriver, an act which ultimately results in the musician s death. The story is comprehensively covered by the media, and the public response is one of outrage at such a senseless attack. This case represents a plethora of similar stories which have come into the public eye, many of which are unified by gruesome details and the same mental disorder shared by the perpetrators: schizophrenia. Schizophrenia is a chronic, disabling mental disorder, affecting approximately 1% of the population and is the most common form of psychosis. The question of whether schizophrenia increases the risk of violence is not a new one, and has been widely debated and researched over the past few decades. Understanding whether individuals with this condition are more violent, or if there is any relationship at all between schizophrenia and aggressive acts, is a crucial one to understand. Any association has far reaching consequences, particularly in terms of the risk posed to the public by these individuals, the prevention of violent acts committed by schizophrenia sufferers, and the impact on the focus of mental health services and policy. The subject also represents an emotive topic which is ultimately heavily influenced by public perception of mental disorder, media coverage of violence committed by mentally disordered individuals and the perpetuation of stigma faced by those living with schizophrenia. This essay will review the extant literature on the association between schizophrenia and violence, evaluating the role of specific risk factors such as substance abuse and symptomatology, and will also present a discussion of the public health issues arising from this topic. Literature Review Early large scale epidemiological studies looking specifically at psychiatric disorders and violence in the community first put forward the view of an association between schizophrenia and violence. Swanson, Holzer, Ganju & Jono (1990), in a study of over 10,000 people, found that individuals with mental illnesses living in the community engaged in more violent behaviour than those without mental illness % of individuals with schizophrenia engaged in violent behaviour compared with only 2.05% of those with no disorder.. Since then, a wealth of research has led to the conclusion that there is a small, but significant, association with violence amongst populations of individuals with schizophrenia (Douglas, Guy & Hart, 2009; Fazel, Gulati, Linsell, Geddes & Grann, 2009; Elbogen 1

2 & Johnson, 2009; Steadman et al., 1998). There remains a lack of agreement, however, on what it is about a population of mentally disordered individuals which increases their propensity to act violently. This failure to reach a consensus stems from different ideas and conflicting research findings, and will be seen throughout this literature review. One of the main debates in this field centres around whether it is characteristics of schizophrenia itself which increases the risk of violence amongst these individuals, or some separate but co-occurring issue such as an overrepresentation of static risk factors predisposing individuals to violence amongst schizophrenia populations, or mediation through comorbidities (namely substance abuse). The degree to which the risk of violence may be elevated in these groups is also hotly debated, with rates suggested remaining inconsistent and varying widely. This literature review will discuss proposed theories behind the association between schizophrenia and violence, whether the apparent increase in risk can be attributed to the mental disorder itself, and key methodological variation which may influence discrepancy in this area. Static Risk Factors Of those studies which have found that individuals with serious mental illness are more likely to engage in violence than non-psychiatric populations, a consistent pattern emerges within social demographics of perpetrators; the type of person with schizophrenia who engages in violence is remarkably similar to the type of person without schizophrenia who engages in violence. In a study of over 30,000 participants, Elbogen and Johnson (2009) found that the most serious violent acts were predicted by having a history of violence, being male and being young risk factors which have been revealed to be key demographic characteristics of non-mentally disordered violent individuals, along with other variables such as low socioeconomic status (Swanson et al., 1990). Elbogen and Johnson (2009) also found that severe mental illness alone did not independently predict future violent behaviour. This suggests that it is the presence of other risk factors amongst psychiatric populations which may ultimately lead to violence. Of course, many of the described risk factors are overrepresented in psychiatric populations schizophrenia is more common in young males, after all, and these individuals are often of low socioeconomic status in this way, a group of individuals with schizophrenia may be at an increased risk of violence as compared to a group of individuals without schizophrenia; but at the individual level, mental illness has much less of an association with violence than intrinsic factors already present in the individual. 2

3 Substance Abuse A widely held opinion is that any association which exists between schizophrenia and violence can be explained by the increased presence of comorbid conditions in severe mental illness populations namely, substance abuse. Whilst Elbogen and Johnson (2009) found no statistical relation between the incidence of violent behaviour and severe mental illness alone, when comorbid substance abuse was present the relationship became significant. This suggests any increased rate of violence in a population of individuals with schizophrenia may be due to a higher rate of substance abuse - indeed, this study revealed 46% of those diagnosed with mental illness also had a lifetime history of comorbid substance abuse/dependence. These authors concluded that their results demonstrated that an individual with a severe mental illness but no co-existing substance abuse or history of violence has the same chances of committing any violent act within the next 3 years as a non-mentally ill person in the general population; i.e. schizophrenia as a construct in and of itself is not associated with violence. Fazel et al. (2009) added support to this claim through a comprehensive meta-analysis. There were several main findings. In all studies analysed, the risk of violent behaviour was increased in individuals with schizophrenia and other psychoses as compared to the general population, with all the odds ratios being greater than 1. These odds ratios, although widely heterogeneous, substantially increased when comorbidity with substance disorders was present the pooled odds ratio estimate result was then four times higher as compared to individuals with schizophrenia without these comorbidities. This overall increased risk in patients with mental illness and co-occurring substance abuse, however, was no different to the risk of violence in individuals with substance abuse disorders alone. The addition of a mental health disorder appeared to confer no extra risk of violence than that caused by substance abuse alone. Findings such as this have thus been used to suggest substance abuse may represent a causal mediator in the pathway between schizophrenia and violence. The relationship between schizophrenia and substance abuse in determining violence, however, is unlikely to be a simple one. Mullen (2006) suggests that substance abuse as a cause of violence could only be accepted if the presence of a third factor mediating both violence and substance abuse can be excluded. Mullen suggests personality traits, such as those frequently associated with psychopathy e.g. impulsivity and antisocial behaviour which have been found at increased rates in violent schizophrenia patients compared to non-violent patients (Nolan, Volavka, 3

4 Mohr & Czobor, 1999) may potentially account for this third factor. This may represent an interplay between static risk factors and dynamic ones in the pathway to violence. Wallace, Mullen and Burgess (2004) examined the criminal records of 2861 people with schizophrenia on their first admission to hospital over a 25 year period from 1975 to 2000, comparing them to matched community individuals. The rate of substance misuse amongst schizophrenia patients increased dramatically, rising from 8.3% in 1975 to 26.1% in The rate of criminal convictions rose in a more modest fashion, from 6.6% to 10.3% in the same time period in line with the increase in the control group (1.1% to 2.8%). These findings again point to a more complex relationship between substance abuse, schizophrenia and violence, suggesting that substance abuse alone cannot solely account for violence otherwise, it would be expected that violence rates and substance abuse rates would rise proportionately. Diagnosis vs Symptoms A key question when examining schizophrenia and violence is that of whether it is sufficient to look at schizophrenia as an overarching diagnosis, or whether individual symptoms can explain the association between violence and this disorder. Psychosis and Violence. Strong evidence has emerged which points to psychosis as a key variable in any increase in violence observed in populations of schizophrenia patients. In a large meta-analysis of 204 studies where a total of 885 effect sizes were calculated, psychosis was significantly associated with a 49 68% increase in the odds of violence (Douglas et al., 2009). Furthermore, when psychotic-like experiences occur in the general population, these people are at increased risk of attacking another person and being arrested for assault (Mojtabai, 2006). Taylor (1985) interviewed prisoners remanded on violent charges with respect to their psychiatric histories and concluded that 20% of those with psychosis were directly driven to offend through their psychotic symptoms, and the offences of a further 26% were probably due to these symptoms. Whilst psychosis is a cardinal feature of schizophrenia, it is also found in many other mental disorders for example bipolar mood disorder and severe depression. It is a heterogeneous syndrome which includes delusions, 4

5 hallucinations and behavioural disturbances. Within psychosis, certain symptoms co- occur to form 3 sets of well described symptomology clusters positive, negative and disorganised symptoms. This indicates that whilst it is reductionist to simply look at the association between schizophrenia and violence based on diagnosis of the disorder, it may also be so to examine psychosis as a uniform set of symptoms. Indeed, Swanson et al. (2006) interviewed 1410 schizophrenia patients from institutions across the United States about violent behaviour in the last 6 months. Positive symptoms of schizophrenia increased the risk of minor and serious violence. Interestingly, the presence of negative symptoms (such as social withdrawal) resulted in lowered risk of serious violence. The positive symptoms described here included delusions and hallucinations, demonstrating that psychosis can be examined in even further detail by examining these symptoms specifically. Delusions and Violence. Early evidence for the importance of delusions as causing increased risk of violence amongst patients of schizophrenia comes from Link, Andrews, and Cullen (1992). In an epidemiologic study of current and former psychiatric patients and community residents with no psychiatric history, former patients were found to be significantly more violent than the community residents - a difference which was accounted for entirely by psychotic symptoms. A further study revealed this difference to be due to a specific subset of delusional symptoms, termed threat/control/override ( TCO ) delusions. These delusions lead the individual to fear harm to themselves (threat) whilst also blocking internal constraints against violence (control-override) in precipitating aggression (Link & Stueve, 1994, in Douglas et al., 2009). This would suggest that a delusion which led the individual to believe that external forces were controlling their thought processes combined with fear of being harmed would result in an increased tendency towards violence, whereas other delusions (e.g. delusions of grandeur) would not. The findings from Swanson, Borum, Swartz & Monahan (1996) that TCO symptoms on the diagnostic interview schedule were more strongly associated with violence than other psychotic symptoms supports this view. Other research failed to replicate a relationship between TCO delusions and violence. A series of methodologically robust seminal papers using data from the MacArthur Violence Risk Assessment Study (Steadman et al., 1998; Appelbaum, Robbins & Monahan, 2000) provided a prospective, multisite data set from 1136 individuals recently discharged from psychiatric hospitals and focussed on violence, following individuals for 1 year and collecting information at various intervals throughout this time. Previous research had relied on retrospective data and 5

6 thus this study allowed a realistic study of any association between delusions and violence. These investigations revealed no association between delusions and risk of violent behaviour, even when TCO delusions specifically were assessed. Appelbaum et al. (2000) offered several explanations for the failure to replicate previous findings between TCO delusions and violence. It was suggested that differences could be attributed to inherent problems trying to compare retrospective data with prospective data, with previous associations being merely an artefact of the retrospective method. Indeed, when data was then analysed retrospectively, an association between TCO delusions and violence emerged. Another suggestion was that there may indeed be an association between delusions and violence acts, but as delusions are often associated with long term psychotic illnesses which result in a withdrawal from social life, there are simply decreased opportunities to engage in interpersonal exchanges, resulting in overall decreased opportunities to engage in the sorts of interactions which can ultimately lead to violence. Methodological Issues A major issue in understanding the true relationship between schizophrenia and violence stems from the lack of methodological consistency used in these studies. Some of the methodological differences and their limitations are discussed below. Defining the Exposure. Early research included schizophrenia under a heterogeneous collection of other disorders (e.g. Steadman et al., 1998; Hodgins et al., 1996, as cited in Walsh, Buchanan and Fahy, 2002) and do not always give results broken down by diagnosis. Whilst more recent studies have moved into analysing schizophrenia as a discrete category, diagnostic techniques vary wildly. Studies may rely on case note diagnoses or registers made at patient discharge, which are dependent on the diagnosing clinician s individual judgements, whilst others rely on techniques employed at the time of data collection e.g. research based interview measures (Crocker et al., 2005). It can be difficult to compare findings of these studies, therefore, as no agreed diagnostic procedure for studies in this field exists. Defining the Outcome. 6

7 The way in which violence is defined and measured is a key way in which these studies vary. The actual behaviours which are deemed to constitute violence differ; some papers only look at extreme forms of violence (e.g. homicide) (e.g. Schanda et al., 2004) whilst others use more minor forms of violence e.g. pushing someone, or even just verbal threats of violence (Troisi et al., 2003, as cited in Douglas et al., 2009). Unsurprisingly, different definitions of violence appear to result in different rates of violence being found Information on violence has been garnered variably from single (self-report, official records) or combined sources of information. These single sources may represent some of the greatest limitations, especially those relying on self-report and informants; Social bias may have a particularly strong role in these measures, with participants potentially underreporting violent behaviour either for acceptability reasons or fear of retribution. Official records equally may not accurately reflect levels of violence; for example, all records are subject to documentation errors and arrest records reflect quality of policing in an area rather than being an accurate reflection of violence levels. Walsh et al. (2002) suggest this makes the evaluation of the association between schizophrenia and minor forms of violence extremely difficult if these sources are used. Combined sources of information appear to offer the most accurate estimates of violence prevalence; Steadman et al. (1998) demonstrated how using 3 sources of information resulted in a prevalence of 27.5% in a group of discharged psychiatric patients as compared to a 4.5% when only a single source was used. Approach and Study Design. Cross sectional studies often look at individuals with schizophrenia at various points in the hospitalisation process and assess violence within this group. High rates of violence have been found particularly in patients prior to hospitalisation (e.g. Humphreys, Johnstone, MacMillan, & Taylor, 1992, who estimated that 20% of 1 st admission patients with schizophrenia had behaved in a life threatening manner before admission) and during hospitalisation. Comparing patients at different points in the hospitalisation process is likely to invoke different confounding factors increased symptomatology on admission may affect an individual s propensity to violence. Furthermore, most individuals with mental health disorders are not hospitalised (Robins and Reiger, 1991, as cited in Walsh et al., 2002), so whether these findings could be deemed representative of all patients with schizophrenia is called into question. In this way, studies examining both patients pre-hospitalisation and during hospitalisation may overestimate any association between schizophrenia and violence. 7

8 The Issue of Causality. A final, key methodological problem in research in this area relates to causality. Investigations into the relationship between schizophrenia and violence have sought to describe variables which can explain the pathway from schizophrenia to violence, but the way in which causality has been defined may be insufficient to confidently draw these types of conclusion. A key criterion for establishing causation is temporal ordering i.e. mental illness should precede violence. Whilst many studies incorporate this into their methods using prospective studies, for example Van Dorn, Volavka & Johnson (2010) argue that temporal ordering neglects a key aspect of establishing casual relationships; that of temporal proximity. The frequent use of lifetime diagnoses (a diagnosis given at any point in an individual s lifetime) as opposed to diagnosis in say, the last year, not only hinders the ability to discuss the role of symptomatology, but considers mental health as a static construct, present continuously at the same severity. Analyses using lifetime diagnosis may well suppress whatever relationship may exist between schizophrenia and violence; this approach assumes presence of the risk factor of mental illness without accounting for the fluctuating course of disease. There may be variation amongst individuals with some being in an active stage of the disease, or alternatively be in a period of remission and thus not displaying the risk factor under investigation during the time period being examined for violent behaviour. Temporal proximity is thus lacking in this approach, and biases any study in favour of not finding an association. Van Dorn et al. (2010) suggested that this misunderstanding of temporal association in causal pathways has resulted in a lack of association at times being found between schizophrenia and violence in the absence of comorbid substance abuse (e.g. Elbogen & Johnson, 2009). When Van Dorn et al. (2010) reanalysed the NESARC data looking only at diagnosis of mental illness in the past year (i.e. temporally relevant diagnoses), a modest but significant relationship between serious mental illness and violence arose. Conclusions from the Literature Despite the vast range of methodological techniques used in this field, the majority of studies and several large meta-analyses do seem to point to a modest statistical association between schizophrenia and violence. It remains unclear what exactly is causing this increased violence, but ultimately it is unlikely to be just one variable. 8

9 Static risk factors are likely overrepresented in these populations, and an interplay between substance abuse and psychotic symptoms specifically may increase the perpetration of violent acts. In the future, research should continue to focus on temporal proximity to explore the variables proposed here to fully elucidate causal pathways between schizophrenia and violence. A final point to make relates to the way in which risk is typically reported. Most research concludes with an evaluation of relative risk i.e. the amount of risk posed by individuals with schizophrenia as compared to those without. Focussing on relative risk, however, tells us little about the true risk posed to the general population by individuals with schizophrenia. A more useful measure may be population attributable risk percent (PAR%), which refers to the percentage of violence within a population which can be ascribed to schizophrenia and could therefore be eliminated if schizophrenia itself were eliminated from the population. When PAR% is measured, the overall contribution to violence in the population by mental illness is smaller than that suggested by relative risk. Coid et al. (2006), in a comparison of PAR% of psychiatric disorders found that psychosis positive individuals had the lowest PAR% at just 0.7%. This demonstrates that whilst a group of individuals with schizophrenia may be at increased of engaging in violent behaviour, if this risk were reduced to the average risk of engaging in violence then the effect on current rates of violence amongst the general population would be negligible. A stronger focus on PAR% presents a more balanced view of schizophrenia s real world contribution to violence. Schizophrenia and Violence: A Public Health Perspective The nuances of any existing association between schizophrenia and violence is important to establish due to the implications of this relationship on various public health issues. This section will briefly discuss these issues in relation to various matters. Implications for Individuals with Schizophrenia Individuals living with schizophrenia represent one of society s most stigmatised and rejected groups (Angermeyer & Dietrich, 2006). Stigma has a huge impact on these individuals, and results in decreased uptake of mental health services, contributes to social isolation, and leads to feelings of hopelessness (Rüsch, Angermeyer, & Corrigan, 2005). Violent victimisation of individuals with schizophrenia is 14 times more common than the 9

10 perpetration of violence by this group (Brekke, Prindle, Bae & Long, 2001), acts which are likely to be motivated by stigma. Victimisation has even been proposed as an explanation for increased violence amongst mentally disordered people (Hiday, Swanson, Swartz, Borum & Wagner, 2001), where repeated victimisation results in stressful situations and retaliation by the victimised individual. Much stigma has its roots in public perception of individuals with schizophrenia as violent, with the media playing an important role in perpetuating this view (Torrey, 2011). The general public feel that the mentally ill are more likely to be violent (Appelby and Wessley, 1988, as cited in Stark, Paterson & Devlin, 2004), with schizophrenia being viewed with more apprehension and fear than other psychiatric conditions (Crisp, Gelder, Rix, Meltzer & Rowlands, 2001). Media reports of the rare times a person diagnosed with schizophrenia is violent are often sensationalist, using emotive language and overly simplified versions of events (Stark et al., 2004). Ultimately, this leads to cognitive biases which heighten the perception of the mentally ill as an imminent and unstoppable threat to the public, and over-exaggerate the association between mental illness and violence. When individuals with schizophrenia do engage in violence, they are more likely to be incarcerated than violent individuals with no mental illness (Wallace et al., 2004). In prison, these individuals may be subject to decreased access to mental health care and suffer poor outcomes - Keers, Ullrich, DeStavola & Coid (2014) demonstrated the emergence of persecutory delusions amongst untreated prisoners with schizophrenia, for example. The cost of incarceration and hospitalisation/detention of these individuals is also not insignificant, and represents a portion of the cost of these individuals to society. Indeed, the financial burden of schizophrenia is immense, with the total cost in the UK of this group being estimated to be 6.7 billion in 2004/5 ( 2 billion in direct costs and $4.7 billion in indirect costs e.g. loss of productivity) (Mangalore & Knapp, 2007). A complete understanding of whether schizophrenia actually does increase the risk of violence is necessary either to dispel the widely perceived view of the public that schizophrenia increases violence and thereby decrease stigma towards these groups of patients, or, if there is an association, to fully understand and educate the public of the realities and limitations of this relationship. Mental Health Policy and Risk Assessment 10

11 A presumed association between schizophrenia and violence has been used to justify mental health policy, and the emphasis on risk assessment by mental health professionals. Public perception and the role of the media is again of relevance here; media coverage of violent acts consistently relates these incidents with failings in the mental health system, and both explicitly and implicitly suggest that services, or even individuals, have failed in their duty of responsibility to care for these patients (Stark et al., 2004). Hewitt (2008) suggests that concerns regarding some of the widely publicised acts of violence committed by individuals with schizophrenia throughout the 1990s have motivated the contemporary legislative movement focussing on control in the community of these patients e.g. the Care Programme Approach (1991) and Supervised Discharge (1996) policies, which tightened control over the patients deemed highest risk in the community. These legislative changes have been suggested to be due to a governmental reaction to regaining pubic confidence rather than due to any response to patient s mental health needs (Paterson & Stark, 2001). An increasing conflation of madness with dangerousness in public perception may also have unintended consequences on how risk assessments are used. Stein (2002) found that concern over risk assessments being used as proof of failure in responsibility to predict violence should a violent act take place acted to encourage untruthful completion of these tools. Similarly, Paterson and Stark (2001) unveiled a culture of fear and blame amongst mental health nurses associated with underestimating risk. In cultures such as these, mental health professionals may take the approach of subjecting more individuals to involuntary detention than would necessarily go on to commit a violent act. The ability of risk assessment tools (e.g. the HCR-20) to predict violence also ties into the clear understanding of the link between schizophrenia and violence. These tools are frequently employed in the management of individuals with schizophrenia, and appear to be able to define people at high risk of becoming violent but are not able to state with any certainty whether any particular high risk individual will become violent. As such, their utility has been called into question. Coid, Kallis, Doyle, Shaw and Ullrich (2015) carried out a prospective cohort study of over 400 male and female patients discharged into the community, where the HCR-20 was measured pre- and post- discharge and acts of violence were also assessed. It was found that this tool was a poor predictor of violence, with 8 items on the HCR 20 being unable to predict violent behaviour better than chance. 11

12 The authors of this paper argue that standardisation of risk assessment tools uses predictive modelling i.e. risk factors are measured once and then used to statistically predict the occurrence of violent acts within some subsequent time. Although this method accounts for temporal ordering of the risk factor and violence, it does not necessarily account for temporal proximity. As previously discussed, temporal proximity has been put forward as a key variable in understanding causal links between schizophrenia and violence. Coid et al. (2015) raise the question of whether risk assessment tools developed on predictive modelling such as the HCR-20 represent the most appropriate clinical goal. Whilst they are useful in identifying individuals who may go on to commit a violent act, if the overall clinical aim is to prevent acts of violence in high risk individuals then tools based on this model of statistical prediction are of limited use the only way risk can be reduced is by targeting those factors which are known to be driving violence, i.e. causal factors in the pathway between schizophrenia and violence. Coid et al. (2015) suggest that these tools could be further developed through a greater focus on causal rather than predictive statistical modelling in order to progress from risk assessment to effective risk management. Risk management may centre around drug and alcohol treatment programmes if substance abuse could be identified as a causative variable, or early treatment of psychotic symptoms. Treatment with antipsychotics in particular appears to play a role in reducing the risk of violence - Swanson et al. (2008) found that violence decreased from 16% to 9% in individuals treated with antipsychotics for 6 months. Generally, adherence to medication was associated with a reduction in violence prevalence. Conclusions A small but significant association between schizophrenia and violence likely exists, but there has been insufficient focus on risk drivers causing this association as opposed to merely identifying risk factors which may only correlate with violence in populations of individuals of with schizophrenia. Whilst several explanatory variables have been proposed, a failure to establish causation may have resulted from both the diversity of methodological approaches used in this field and a failure to consider temporal proximity. Proposed causative variables should be investigated with regard to temporal proximity to properly understand the nuances of the pathway between schizophrenia and violence, which is likely to be complex and multifaceted. The establishment of a causal pathway is crucial for management, as well as assessment, of risk. Whilst causal pathways still need to be further investigated to identify main contributors to the pathway towards violence, likely risk management approaches will focus on both 12

13 substance abuse programmes and controlling symptomatology as these appear to be both the most easily targeted variables and have the largest wealth of evidence to support their role in this pathway. Establishing the details of this pathway may not only be used to form effective management strategies but can also be used to inform the public of the true risk of schizophrenia in society, which is likely to be low, and as such have far reaching consequences in public health issues. Schizophrenia, therefore, probably does increase the risk of violence - but the pathway needs further clarification focussing specifically on causative variables. A final comment is that more research in this area is needed into specific forms of violence. Much work has investigated the link between especially serious crimes such as homicide, but there is a shortage of research specifically investigating less sensational acts of violence. Intimate partner violence, for example, may represent different pathways to violence as compared to a homicidal act towards an unknown individual on the street. This sort of violence is likely frequent and underreported, and may present a more salient public health concern than the acts publicised by the media and often investigated in this field. This thus represents an area of research which should be focussed on in the future. Word Count:

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