Clinical Psychology Review 31 (2011) 711–726

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Clinical Psychology Review

Risk factors for violence among patients with schizophrenia

Sune Bo a,⁎, Ahmad Abu-Akel b, Mickey Kongerslev a, Ulrik Helt Haahr c, Erik Simonsen a

a Psychiatric Research Unit, Roskilde, Denmarkb Los Angeles, California, USAc Early Psychosis Intervention Center, Roskilde, Denmark

⁎ Corresponding author at: Psychiatric Research UnitE-mail address: subh@regionsjaelland.dk (S. Bo).

0272-7358/$ – see front matter © 2011 Elsevier Ltd. Aldoi:10.1016/j.cpr.2011.03.002

a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 September 2010Received in revised form 24 February 2011Accepted 2 March 2011Available online 23 March 2011

Keywords:SchizophreniaViolencePersonality disordersPsychopathyPsychosesMentalizing

Studies of birth cohorts show evidence of greater risk of violence among patients with schizophreniacompared to the general population. However, the contribution of schizophrenia to violence is heavilydebated and remains unclear. This debate has spurred research whose focus can be associated with one ofthe following areas: psychotic symptoms, personality disorders (in particular psychopathy), mentalizingabilities, substance abuse and demographic factors. The aim of the current review is to evaluate the predictiverole of these risk factors in the occurrence of violence among patients with schizophrenia. We identified twodifferent trajectories for violent behavior in schizophrenia: one pertains to patients with no prior historyof violence or criminal behavior and for whom positive symptoms appear to explain violent behavior,and another where personality pathology, including psychopathy, predict violence, regardless of othersymptomatology associated with schizophrenia. Furthermore, emergent data suggest that specificmentalizing profiles can be associated with the occurrence of violence in schizophrenia, an issue thatwarrants further consideration in future research.

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7121.1. Purpose and outline for the article . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7121.2. Method: search criterion and data-bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712

2. Schizophrenia and violence — an overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7123. Methodological issues in current research on schizophrenia and violence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714

3.1. Definition of violence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7143.2. Demarcation of schizophrenia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7143.3. Study designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7143.4. Categorical versus dimensional approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7153.5. Confounding factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715

4. Risk factors for violence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7154.1. Psychoses and psychotic symptoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7154.2. Personality traits and personality pathology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7164.3. Mentalizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7174.4. Substance abuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7184.5. Demographic factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718

5. Treatment approaches to violence in schizophrenia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7196. Closing remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721

1 64 62 98.

712 S. Bo et al. / Clinical Psychology Review 31 (2011) 711–726

1. Introduction

1.1. Purpose and outline for the article

A widely accepted avowal is that schizophrenia augments the riskfor violence. This assertion spurred a plethora of clinical articles (e.g.,Bjørkly, 2002b; Bradford, 2008; De Pauw & Szulecka, 1988; Douglas,Guy, & Hart, 2009; Junginger, 1996; Monahan, 1992; Mulvey, 1994;Taylor, 2008), yielding divergent and often contradictory results.This is also reflected in a variety of reviews and meta-analyses thatintended to sort out the nature of this relationship. These reviewsmake clear the complexity of the field and the different point ofviews that one can take when investigating violence in patients withschizophrenia. A summary of the themes and conclusions of some ofthe most prominent reviews conducted on the subject over the pastdecade or so is presented in Table 1.

In light of the prevailing divergent views regarding the nature ofthe relationship between violence and schizophrenia, the presentreview is an attempt to further clarify this relationship. To this end, wefirst present an overview of the relationship between violence andschizophrenia followed by a discussion of key methodological issuesthat could impinge on the nature of this relationship.We then evaluatewhether schizophrenia enhances violence at all by addressing thefollowing key questions: 1) Do psychotic symptoms enhance violenceamong patients with schizophrenia? 2) Do certain personality traitsor specific personality pathology have bearing on the occurrence ofviolence in schizophrenia? 3) Are mentalizing abilities or disabilities aprovoker of violent behavior in schizophrenia? 4) Can substance abuseamong patients with schizophrenia be perceived as a factor contrib-uting to violence? And finally, 5) what role does sociodemographicvariables such as gender, age and socioeconomic status have in theoccurrence of violence among patients with schizophrenia? We thenreview key treatment approaches and their impact on the occurrenceof violence. In the final sectionwe summarize themain findings of thisreview and speculate about how these risk factors might interact tolead to violence.

1.2. Method: search criterion and data-bases

The current review is informed by computerized PubMed, Psycinfoand Embase searches from 1980 through December 2010, using the

Table 1Major reviews and meta-analyses assessing the relationship between schizophrenia and vi

Reference Theme

Bonta et al. (1998) Meta-analysis on factors predicting criminal recidivism,mentally disordered, including schizophrenia and non-doffenders

Douglas et al. (2009) A meta-analysis on the contribution of psychosis on viol

Fazel et al. (2009b) A systematic review and meta-analysis on studies investrelation between schizophrenia and violence, including

Hodgins (2008) A review article on schizophrenia, aggression and treatmimplications

Modestin (1998) An overview of the relation between mental disorders, scand violence,

Nielssen and Large (2010) Rate of homicide during first episode psychosis and afte

Taylor (2008) A review on the relation between psychosis and violencspecific focus on schizophrenia

Walsh et al. (2002) A review on violence and schizophrenia

Volavka and Citrome (2008) A review of the relation between schizophrenia and theheterogeneity of violence, including moderating factorspersonality disorder

terms schizophrenia, mental disorders, violence, aggression, personalitydisorders, psychopathy, mentalizing and Theory of Mind. A number of995 articles were found. In the initial screening process, the abstractsof each of these articles were read. All the relevant papers were thenhand searched for other relevant references, resulting in 258 articlesthat were considered for the purposes of the current review.

In this paper, we opted for a review of the literature rather than asystematic quantitative review for several reasons. First, numerousstudies addressing the relation between schizophrenia and violencehave been beleaguered with methodological flaws (Douglas et al.,2009), which makes it difficult to combine studies yielding valid andreliable scores with studies that do not. For example, definitions ofintrinsic terms, particularly the definition of schizophrenia, as wellas the diagnostic procedures employed vary widely across studies(see Section 3.2 for further details). Second, both dependent andindependent variables constructs vary across the different studies,making it inappropriate to calculate a general effect size. This vul-nerability raises the question whether the concepts and diagnosticcategories can reliably be quantitatively calculated without engagingin the mistake of mixing apples and oranges. Finally, the foci of themany studies, including meta-analyses, are quite diverse, with someinvestigating psychosis and violence, others studying schizophreniaper se and violence, and yet some others studying the symptomatologyassociated with schizophrenia and violence or criminality.

With this in mind, a narrative review of the literature, rather thana systematic quantitative review, seems appropriate (Bailar, 1997;George, 2001). This approach affords us the opportunity to adopt acritical stance ofmajor streams in the literature, discuss and synthesizedisparate findings, and in light of this, point out some methodologicalconsiderations that will hopefully aid future research in clarifying therelationship between schizophrenia and violence.

2. Schizophrenia and violence — an overview

Studies still diverge in their conclusions regarding the relationshipbetween violence and Schizophrenia. Until the 1980s, it was broadlyaccepted that having a major mental illness was not a risk factorfor violence (Bonta et al., 1998; Rabkin, 1979; Sheridan & Teplin,1981). For example, Teplin (1985) argued that not enough evidenceexisted to prove a connection between mental illness and violence,and Monahan (1995) claimed that the research was too scarce to

olence.

Main conclusion

comparingisordered

Same variables predict criminal recidivism in both mentallydisordered and non-disordered populations

ence Moderating factors more essential as predictors of violence thanpsychosis

igating thehomicide

Schizophrenia predicts violent offending, but the excess risk ismediated by substance abuse comorbidity

ent Schizophrenia contributes to violence, but in patients with a historyof early violent behavior, psychotic symptoms has little influence

hizophrenia Schizophrenia contributes to violence, and is enhanced withcomorbid psychoactive substances

r treatment. Rate of homicide is disproportionately high compared to aftertreatment in schizophrenia. First-episode psychosis is a major riskfactor for violence.

e with Schizophrenia contributes to violence in groups of patients with nocriminal behavior before illness onset, but not in groups with priordelinquencyThe association between schizophrenia and violence is confirmed,but mediated by substance misuse

such asSchizophrenia contributes to violence in groups of patients were nohistory of violence is found

713S. Bo et al. / Clinical Psychology Review 31 (2011) 711–726

support any unyielding conclusions. Current research still lendssupport to this view. In a meta-analysis of variables contributing torecidivism, Bonta et al. (1998) underscored that neither psychoses norpsychotic symptoms had any influence on violence, and severalstudies were not able to confirm the association between schizophreniaand violence among civil patients (Appelbaum, Robbins, & Monahan,2000), criminal offenders (Arboleda-Flórez, Crisanti, & Holley, 1995) orthe general population (Swartz & Lurigio, 2004).More recently, Elbogenand Johnson (2009)maintain thatviolence lacks any substantial relationto psychoses, or schizophrenia in general. Research even suggests thatthere is a slight negative relation between schizophrenia and violence(Appelbaum et al., 2000; Monahan et al., 2000; Steadman et al., 1998).The overall finding of this body of research is that schizophrenia andpsychoses have minor, if any, influence on violence in patients, andthat among forensic populations “the presence of schizophrenia andpsychotic symptoms exhibited around the time of the index offenseor admission to hospital were negatively related to risk. Psychosis,psychotic symptoms, and exacerbation of those symptoms have littlevalue as indicators of the risk of violence in offender populations”(Quinsey, Harris, Rice, & Cormier, 2006, pp. 113).

Contrary to this view, a large body of research asserts thatschizophrenia is associated with aggressive behavior and an increasedrisk for violent and non-violent crime (Cheung, Schweitzer, Crowley,& Tuckwell, 1997a; Hodgins, 2008; Nestor, 2002; Soyka, Graz,Bottlender, Dirschedl, & Schoech, 2007; Swanson, Holzer, Ganju, &Jono, 1990), and more generally, that psychotic disorders have theclearest association with violence (Arseneault, Moffitt, Caspi, Taylor,& Silva, 2000; Bjørkly, 2002a, 2002b; Bloom, 1989; Bradford, 1983;Brennan, Mednick, & Hodgins, 2000; De Pauw & Szulecka, 1988;Junginger, 1996; Krakowski, Jaeger, & Volavka, 1988; Lindqvist &Allebeck, 1990b; Monahan, 1992; Mullen, Burgess, Wallace, Palmer, &Ruschena, 2000; Tardiff, 1984; Tiihonen, Isohanni, Räsänen, Koiranen,& Moring, 1997; Wessely, Castle, Douglas, & Taylor, 1994). This hasbeen demonstrated in various populations including the generalpopulation (Brennan et al., 2000), criminal offenders (Etherington,1993), forensic patients (Erb, Hodgins, Freese, Müller-Isberner, &Jöckel, 2001), and civil patients (Aarsland, Cummings, Yenner, &Miller, 1996). Some even claim that violence and schizophrenia arecausally related (Walsh, Buchanan, & Fahy, 2002).

Cohort-studies support this view and report significant associationbetween schizophrenia and violence. In a cohort study where 12,058people were followed for 26 years, the risk factor for violence amongpatients with schizophrenia was 7 times higher than that of peoplewithout a mental illness (Tiihonen et al., 1997). Moreover, in acomprehensive investigation of hospitalization and criminal convic-tions among patients with a mental illness that were drawn froma birth cohort of 358,180 individuals, Brennan et al. (2000) reportthat individuals who were hospitalized for schizophrenia wereassociated with increased engagement in violence compared topatients who were never hospitalized. This association was, to someextent, independent of substance abuse and demographic variables.Similarly, in a study that included 961 adults, Arseneault et al. (2000)report that schizophrenia was distinctively associated with violenceeven when controlling for demographic risk factors and comorbidconditions such as substance abuse, manic and anxiety disorders.

The link between schizophrenia and violence was also concludedin a number of retrospective studies. Using a 15-year police register,Lindqvist and Allebeck (1990b) traced violent activity of 644 patientswith schizophrenia, and found that these patients were four timesmore prone to exhibit violent behavior than the general population.Another study compared the rate of criminal convictions among 538patients with schizophrenia with a group of non-psychotic psychiatricpatients, matched for gender and age (Wessely et al., 1994). Both menand women with a diagnosis of schizophrenia exhibited increasedviolent behavior compared to the controls. Finally, Mullen et al.(2000) examined two groups of patients with schizophrenia admitted

either in 1975 or 1985, which they compared to the general popu-lation in regard to different types of criminal offenses. Except forsexual offenses, both patient groups displayed significantly morecriminal offenses on all types of criminality compared to the controls.Interestingly, the study revealed that substance abuse accounted for adisproportionate level of offending among the schizophrenic patients,an issue that we will return to later.

Cross sectional studies provide additional insights to the disputeamong researchers with respect to “if” and “howmuch” schizophreniacontributes to violence and offending. In two independent cohortstudies, Volavka et al. (1997) and Humphreys et al. (1992) show thatapproximately 20% of patients with schizophrenia were involved insome kind of violent behavior prior to contact with the health system.Assaults on social workers and other personal working withhospitalized patients with schizophrenia is well documented (Karson& Bigelow, 1987), and it is often hypothesized that many incidentsnever get reported due to work overload and complicated proceduresfor reporting violence, hence the “real” picture might be more severethan estimated in various studies (Walker & Seifert, 1994). Yet itis pivotal to emphasize that violent responses can be a reaction tothe confined setting under which the patients live, more than toschizophrenia per se. As a part of the grand MacArthur RiskAssessment Study, Appelbaum et al. (2000) estimated that amongstdischarged patients suffering from schizophrenia, around 9% showviolent behavior after 20 weeks, which is regarded as low prevalence,compared to other diagnostic groups. However, this does not meanthat schizophrenia is unrelated to violence, nor must be regarded asa shielding factor to violence.

While these studies present a positive relationship betweenschizophrenia and violence, owed to the heterogeneous nature ofthe schizophrenic population, there is a substantial heterogeneityin how much schizophrenia contributes to violence, as well as awidespread uncertainty in regards to the causes underlying thisheterogeneity. In a review on schizophrenia and violence, Hodgins(2008) highlights that schizophrenic offenders are a heterogeneouspopulation with age-differences in onset of violence, variation incriminal and offending career, and a disparity in type and seriousnessof the violence being displayed. Patients who exhibit antisocialbehavior from childhood or early adolescence and continue to offendthroughout their lifetime, they usually engage in violence prior toillness inception. In fact, Abushua'leh and Abu-Akel (2006) showthat improvement in illness condition of schizophrenic patientsmay not reduce the likelihood for violence among those with a highpsychopathic profile, as measured by the Psychopathy Checklist-Revised (PCL-R). Conversely, patients who show no sign of antisocialactivity prior to illness but then commence on an offending trajectoryafterwards, often exhibit chronic course of schizophrenia, and displayserious patterns of violence, including homicide that onsets aroundthe age of forty (Hodgins, 2008). In such population, violence ispredicted to subside with improvement in illness condition.

Moreover, variations in risk ratio of violence among patients withschizophrenia compared to control groups, fluctuates remarkably,ranging from 7-folds (Mullen et al., 2000; Tiihonen et al., 1997) toalmost no contribution (e.g., Elbogen & Johnson, 2009) and even to anegative relationship (Steadman et al., 1998). The wide disparity canbe attributed to the specific participant pool included in these studies,such as homicide offenders, and to overlooking the heterogeneitypresent among patients with schizophrenia (Fazel, Gulati, Linsell,Geddes, & Grann, 2009). Another important factor that mightattribute to this is the time during which patients of schizophreniamight commit violent acts during the course of the disease. A numberof important studies report that the majority of the offendingdisplayed by patients with schizophrenia occurs in first-episodepsychosis (Large & Nielssen, 2011; Nielssen & Large, 2010) and priorto contact with the mental health system (Munkner, Haastrup,Joergensen, & Kramp, 2003; Wallace, Mullen, & Burgees, 2004).

714 S. Bo et al. / Clinical Psychology Review 31 (2011) 711–726

These findings underscore untreated psychosis as a major risk factorfor both violence and homicide in schizophrenia (Appleby & Shaw,2006; Large & Nielssen, 2008; Meehan et al., 2006; Nielssen,Westmore, Large, & Hayes, 2007) and delineate early interventionas vital to impede future violence (Nielssen et al., 2009).

In all, these studies leave us with a somewhat fragmented and notvery clear picture regarding the association between schizophreniaand violence. Research points at diverse directions as to whetherviolence can be accounted for by schizophrenia. This calls for the needto elucidate the underlying causes leading to such grave divisionwithin the field, and ponder whether base-line conclusions, if any, canbe drawn regarding the association between schizophrenia andviolence. In the following sections we address the primary reasonsthat could account for these major discrepancies, and then discussmajor factors that could be associated with the occurrence of violencein schizophrenia.

3. Methodological issues in current research on schizophrenia andviolence

As presented above, results and conclusions regarding the asso-ciation between schizophrenia and violence vary widely acrossstudies, ranging from a causal positive relationship to the lack thereof.However, the methodological weaknesses inherit in many studiesare often overlooked. In this regard, Arboleda-Florez et al. (1998)point out several design flaws such as selection bias, inadequatelycontrolled comparison groups, confounding variables, and poormeasurements of violence, as candidate explanations for theseinconsistencies. Indeed, there is an obvious need to evaluate thesemethodologies in light of the limitations intrinsic to research of thiscomplexity, by which, we hope to elucidate some of the contradictingresults often reported in the literature.

3.1. Definition of violence

One of the most striking observations is that it is virtuallyimpossible to find violence defined in the same way by differentresearch groups (e.g., Douglas & Ogloff, 2003; Monahan & Robbins,2001; Monahan & Steadman, 1994; Mulvey, 1994). Inherit to the firststudies on violence and schizophrenia, was the tendency toconceptualize violence in dichotomous terms—either present orabsent. While more recent studies have elaborated on the nature ofthe violence committed (Kockler, Stanford, Nelson, Meloy, & Sanford,2006; Meloy, 2006), few researchers actually define violence in theirstudies (Alexander, Crouch, Halstead, & Piachaud, 2006).

In defining violence, some include threats and verbal assault (seeDouglas et al., 2009), whereas others only take account of physicalviolence (Monahan & Robbins, 2001; Schanda et al., 2004; Troisi,Kustermann, Di Genio, & Siracusano, 2003). Nonviolent acts such asdamaging property (Cooper, Browne, McClean, & King, 1983; Grassi,Peron, Marangoni, Zanchi, & Vanni, 2001) or self-harming behavior(Barlow, Grenyer, & Ilkiw-Lavalle, 2000; Barnard, Robbins, Newman,& Carrera, 1984) is also included in some studies. Mulvey et al. (1994)showed that substantial differences inwhat constitutes violence couldemerge depending on the source and type of information used. Thissuggests that getting accurate empirical data necessitates employingself-reports in conjunction with collateral information. When relyingon multiple measures for violence, it is important to agree upon whatconstitutes a violent episode in order to mitigate the inconsistenciesthat could transpire from the use of different forms of reports. Howeverin recent years, there has been progress in unifying the definition ofviolence across various studies, where definitions from the Macarthurviolent risk assessment study (Steadman et al., 1998) are being adoptedin recent studies, meta-analyses and systematic reviews (see Large &Nielssen, 2011). Further progress in adopting a unified definition ofviolence would be a significant contribution to the field.

3.2. Demarcation of schizophrenia

Another important methodological issue in studies investigatingthe relationship between schizophrenia and violence relates to howschizophrenia is diagnosed and which assessments and proceduresare followed. Schizophrenia is rarely studied as a single concept(Lindqvist & Allebeck, 1990b; Wessely et al., 1994) but often includedas part of a more heterogeneous group of mental illnesses (Côté &Hodgins, 1992; Hodgins, 1992; Steadman et al., 1998). Assessmentprocedures vary and diagnoses derived from different sources ofinformation such as case-notes, psychiatric registers, and researchinterviews are common. Terms such as schizophrenia, psychoses andmental illness are often intertwined, leaving comparisons studieslimited in generating solid conclusions regarding the relationshipbetween schizophrenia and violence. For a long period, mental illnesshas been conceptualized as a unitary concept in research, probablydue to lack of standardized assessment procedures and a failure toemploy validated and research-based interview measures (Crockeret al., 2005). In reference to the problems associated with the grosscategorization of mental illness, Monahan (1988), in what he refers toas the “impoverished predictor variables” problem, underscores thatin order to predict specific risk-factors for future violence, we mustengage in more fine-grained analysis at the level of symptoms insteadof the broad categories used in many studies. This will allow us to linkspecific aspects of the schizophrenia syndromewith the probability offuture engagement in violent behavior (Junginger, 1996).

Moreover, in the diagnostically reference-systemused inEurope, theICD-10, personality and personality disorders are rarely taken intoconsideration in individuals with a mental disorder as a factor affectingoutcome. The ICD-system is hierarchical, and if a mental disorder isdetected, including schizophrenia, personality disorders are omittedfrom the diagnostic evaluation of the patient. In contrast, themulti-axialstructure of the DSM-system facilitates an inclusion of personalitypathology in the group with mental disorders, and defined as acategorical entity (APA, 2000) rendering it sufficiently distinguishableto warrant an independent identification. Although some researchershave suggested that personality disorders is not truly discernable inpatients with schizophrenia (e.g., Docherty et al., 1986) and thereforeshould be excludedwhenevaluating individualswith schizophrenia,wecontend, as we will show in Section 4.2, that the consideration of theeffect of personality disorders, as a singular construct, on the occurrenceof violence among patients with schizophrenia is warranted.

3.3. Study designs

Studies investigating violence in schizophrenia can be classified intothree man study designs: (1) retrospective studies, (2) prospective/cohort studies, and (3) cross-sectional/survey studies. The majorityof studies conducted in the field of schizophrenia and violence areretrospective studies. These study-designs generally fail to displaycausal or even temporal association between psychopathology andviolent acts (Nolan et al., 2003). This has primarily been attributed tothe temporal gaps between the violent act committed and the rating ofthe psychotic symptoms displayed by the person (Douglas et al. 2009).Even though retrospective studies can approximate the psychoticsymptoms present before or at the time of the violent behavior,inaccuracies could abound due to biases inherent with the recall ofremote violent acts, and as a result, caution has to be exercised whenmaking conclusions about violence in schizophrenia. Nonetheless,retrospective studies can be valuable in framing hypotheses aboutviolence in schizophrenia, which can be evaluated prospectively.

Such prospective studies can in-situ measure and rate the effectand/or association of a number of psychopathological, demographic,personality and behavioral factors on the occurrence of violence. Inaddition to avoiding a number of methodological limitations inherentin any retrospective attempt at defining the condition of the patient

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(Fraguas, 2009), prospective studies allow researchers to drawconclusions of a rather causal nature as opposed to correlationalexplanations often offered in retrospective studies.

Prospective studies can be complemented with cross-sectionalstudies, which are especially relevant for prevalence-rates andfrequencies of certain characteristics in a population at a particularpoint in time. Cross-sectional studies investigating schizophreniaand violence have proven to be valuable regarding the size of therelation between schizophrenia and violence (Humphreys et al.,1992; Volavka et al., 1997). However, since in such studies symptomsand violence are measured at the same point in time, it may notalways be possible to distinguish whether symptoms proceeded orfollowed violent acts. Nonetheless, a cross-sectional study designcan evaluate the interaction of certain variables at a particular pointin time.

In all, while these different study designs have variably contributedto the state of our knowledge regarding the occurrence of violencein schizophrenia, in the present review we find it appropriate toprioritize prospective studieswhen concluding on factors contributingto violence in schizophrenia.

3.4. Categorical versus dimensional approaches

One substantial factor that could explain the inconsistenciesamongst studies pertains to the categorical approach applied whenanalyzing the association between schizophrenia and violence.A common aspect to these studies is their point of departureregarding how the relationship between schizophrenia and violenceis investigated—schizophrenia is considered the independent factorand violence the dependent factor. With schizophrenia being aheterogonous concept with varying phenotypic expressions, investi-gating the contribution of schizophrenia to violence would need toembrace a dimensional approach, where both the specific symptomsconstituting schizophrenia and their magnitude are highlighted inevery single study instead of the currently held broad and somehowdiffuse categorical approach of schizophrenia. Relating aspects andintensity of the symptomatology associated with schizophrenia toviolence, such as demand hallucinations or other clusters of delusions,might be a profitable approach through which we can single outwhich aspects (symptoms) of schizophrenia contribute to violence.An analysis that is based on a dimensional approach rather than acategorical perspective should offer better predictive measurementsfor the occurrence of violence in schizophrenia. The risk of such anapproach, however, would be to lose the broader perspective of thelink between schizophrenia, as a distinct diagnosis, and violence.

3.5. Confounding factors

In this context, a confounding factor is a risk factor for violence thatis associatedwith, but independent of schizophrenia. In a recent study,Tengström, Hodgins, Grann, Langström, and Kullgren (2004) haveshown that the relative association between schizophrenia andviolence is decreased, when controlling for competing risk factorssuch as the presence of psychopathic traits. Moreover, Quinsey et al.(2006) reports that schizophrenia has an inverse relative risk forviolence compared with the risk posed by patients with personalitydisorders or substance abuse. Though research has underlined thatboth substance abuse (especially alcohol) and certain personalitydisorders (Cluster B and psychopathic traits) are evident risk factorsfor engagement in violence, it remains unclear what specific variablesshould be considered as confounders (Arboleda-Florez et al., 1998),especially when taking situational aspects into consideration (Mon-ahan & Robbins, 2001; Mulvey et al., 2006; Skeem & Mulvey, 2001).The causal pathway between schizophrenia and violence thuscontinues to be unclear. However, research addressing the role ofmediating factors holds promise in clarifying the nature of this

relationship. Therefore, future studies should work towards inclusionand not exclusion of these factors.

4. Risk factors for violence

The risk for violence and delinquent behavior among patients withschizophrenia is dynamic and varies as a function of the extent towhichcertain variables such as personality dimensions, substance abuse, andmentalizing abilities are present, and the degree to which environmen-tal events moderate or intensify their expression. Regression-analysesdisplay that comorbid factors other than the symptomatology definingschizophrenia, i.e. positive and negative symptoms, can explain theenhanced engagement in offending and delinquent behavior of patientswith schizophrenia (Douglas et al., 2009). The high prevalence ofcomorbid conditions in schizophrenia underscores that other factorsand diagnoses have a prevailing effect on violence, which should beincluded in risk-assessment research (Douglas et al., 2009). In thecoming sections, we discuss the role of symptomatology, personalitytraits and pathology, substance abuse, mentalizing abilities anddemographic factors as predictors of violence in schizophrenia.

4.1. Psychoses and psychotic symptoms

The preponderance of studies discussing the role of psychoses andpsychotic symptoms in the occurrence of violence, point out that thereis a significant positive correlation between psychoses/psychoticsymptoms and violence among individuals with schizophrenia(Amore et al., 2008; Arango, Calcedo Barba, González-Salvador, &Calcedo Ordóñez, 1999; Cheung et al., 1997a; Cheung, Schweitzer,Crowley, & Tuckwell, 1997b; Douglas et al., 2009; Fazel, Gulati, et al.,2009; Fresán et al., 2005; Hodgins, 2007; Krakowski, Czobor, & Chou,1999; Steinert, Wölfle, & Gebhardt, 2000; Taylor, 2008; Volavka &Citrome, 2008). This association between violence and psychosesappears most prominent during first-episode psychosis, comparedto later stages of the illness (Foley et al., 2007; Milton et al., 2001;Nielssen, 2009; Steinert, Wiebe, & Gebhardt, 1999). In fact, dispropor-tionate levels of violence and severity during first-episode psychosishave been reported for self mutilation (Larger, Babidge, Andrews,Storey, & Nielssen, 2009), suicide attempts (Nielssen, 2009), harmingfamily members (Nielssen et al., 2007), including children (Nielssenet al., 2009), and homicide (Nielssen et al., 2007). Although homicideoccurs very seldom in patients with schizophrenia, and particularlyhomicide of strangers (Nielssen, 2009), it is considered the most sig-nificant complication of psychosis per se.

This association has been confirmed in a recent systematic reviewand a meta-analysis and emphasize that untreated psychosis is amajor contributor to violence and homicide in schizophrenia (Large &Nielssen, 2011; Nielssen & Large, 2010). More specifically, Nielssenand Large (2010) report that there is a 15-fold increase in homiciderates in patients with untreated psychosis compared to patientsreceiving adequate anti-psychotic treatment, and Large and Nielssen(2011) report that prior to anti-psychotic treatment, 1 out of 3patients engaged in some kind of violent behavior, 1 out of 6 in moresevere violence and 1 out of 100 patients commit violence resulting inserious injury. The presence of high rates violence, and especiallysevere forms of violence, during first-episode psychosis and prior toinitial treatment underscore that first-episode psychosis representsa serious risk factor for violence, and that early intervention in themental health system is paramount to curb the occurrence of violence(Large & Nielssen, 2011).

While research strongly support the association between theoccurrence of violence and psychoses per se, there is considerableevidence suggesting that the relation between symptomatology,violence and schizophrenia is not random, but motivated and directedby specific constellations of psychotic symptoms, which primarilybelong to the class of positive symptoms (Angermeyer, 2000; Bentall &

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Taylor, 2006; Hodgins, 2008; Junginger, 1996; McNiel, 1994; McNiel,Eisner, & Binder, 2003; Swanson et al., 2006; Taylor, 2006; Tayloret al., 1998). Delusional symptoms such as persecutory ideations(Swanson et al., 2006), persecutory delusions in combination withemotional distress (Bjørkly, 2002a; Freeman, Garety, & Kuipers, 2001;Nestor, Haycock, Doiron, Kelly, & Kelly, 1995), threat/control-overridesymptoms (TCO) (Arboleda-Flórez, 1998; Bjørkly, 2002a; Hodgins,Hiscoke, & Freese, 2003; Link et al., 1999), command hallucinationsand hallucinations of threatening content (McNiel, Eisner, & Binder,2000; Nolan et al., 2003) have all been found to be significant predictorsof violence and aggression among patients.

In a 12-month follow up study of 128 men with schizophrenia orschizoaffective disorder, Hodgins et al. (2003) found that, whencontrolling for the presence of antisocial personality disorder, thepresence of severe psychotic symptoms, and particularly, the develop-ment of TCO symptoms, was a significant predictor of future violence, insuch a magnitude that neither obligatory community treatment nordepot medications reduced the risk for violence. In addition, Swansonet al. (2006) report, based on a survey of 1410 individuals withschizophrenia living in the community, that positive symptoms, andparticularly those underlying persecutory ideations, as assessed withthe Positive and Negative Syndrome Scale (PANSS), were associatedwith increased tendency to engage in minor or severe violence. Incontradistinction, individuals with high negative psychotic symptomswere significantly associated with reduced risk of serious violence,suggesting that negative symptoms might have a mitigating effect onthe link between positive symptoms and the occurrence of violence, insuch a way that positive symptoms accounted for a significant increasein violence only when negative symptoms were low. A somewhatattenuated association between TCO symptoms and violence, wasreported by Stompe, Ortwein-Swoboda, and Schanda (2004) whereTCO, and particularly those pertaining to unspecified threat symptoms,were only found to be associated with severe violence.

In an attempt to disentangle whether symptomatology contributedto the assessment of patient's violence risk state, as opposed to theviolent risk status, Nolan et al. (2003) examined whether there wasa temporal and causal relationship between psychotic symptomsand assaults of patients with schizophrenia. A direct association wasfound for about 20% of all assaults, which appear to be more frequentlydriven by delusions and hallucinations with threatening content thanby command hallucinations. Interestingly, delusions and commandhallucinations have been linked to both reactive (i.e. impulsive andingenuous) and instrumental (i.e. planned and premeditated) patternsof violence (Felthous, 2008). The occurrence of instrumental violence insome patients with schizophrenia (Barratt, 1991; Houston, Standford,Villemarette-Pittman, Conklin, & Helfritz, 2003), suggest that funda-mental executive functioning associated with planning and structuringare, to some degree, intact in these patients. There is some evidence thatpatients exhibiting instrumental violence generally do not respondto pharmacotherapy (Barratt, Standford, Felthous, & Kent, 1997). Thissuggests that abnormalities precipitating such type of violence arefundamentally different from those underlying impulsive violence(Houston et al., 2003), even though both types of violence could occurunder the same symptomatologic conditions, i.e., under the influenceof delusions and commands hallucinations.

It should be noted that some researchers questioned the associationof the presence of delusions and the occurrence of imminent violenceamong patients with schizophrenia. For example, Appelbaum et al.(2000) report no association between delusions or TCO symptomsand the co-occurrence of violence among recently discharged psychi-atric patients. Similarly, Skeem et al. (2006) report that elevations inTCO symptoms did not increase the propensity to engage in proximateviolence. Rather, the occurrence of violence in the following weekwas subsequent to the previous week in which patients exhibitedincreased anger. However, both of these studies do not rule outthat delusions should never be considered as a risk factor for violence,

but that presence of delusions alone should not be a basis to determineassessment, treatment or management of these patients. Moreimportantly, these studies suggest that the amelioration of symptomsmay not necessarily reduce the risk for violence.

Notwithstanding that psychosis and psychotic symptoms are not theonly risk factors for violence among individuals with schizophrenia,findings clearly underscore the need to structure a thorough treatmenttargeted at psychotic symptoms related to schizophrenia whenpreventing violence. This includes an extensive monitoring of thecourse of illness and symptomatology, particularly during first episodepsychosis, with an explicit treatment program aimed at minimizing theseverity of positive symptoms in these patients. Specifically, threat/control-override symptoms, persecutory ideation, command hallucinationsand delusions and hallucinations with threatening content shouldcarefully be monitored and treated due to their likely direct associationwith the occurrence of aggression and violence.

4.2. Personality traits and personality pathology

Personality disorders (PD) are characterized by “anenduringpatternof inner experience and behavior that deviates markedly from theexpectations of the individual's culture” that is “inflexible and pervasiveacross a broad range of personal and social situations”, andwhich “leadsto clinically significant distress or impairment in social, occupational,or other important areas of functioning” (DSM-IV-TR, 2000, p. 689).Research to-date underscores the importance of accounting for PD inthe understanding of general psychopathology (Kernberg & Caligor,2005; Simonsen, Ronningstam, & Millon, 2008; Strack & Millon,2007) and in explaining the variance observed in individual behavior(Fischer et al., 1997; Magnavita, 2005; Mischel & Shoda, 1998; Shoda &Mischel, 2006). This assertion is bolstered by findings from epidemio-logical studies which show that the prevalence rate for PD in a normalpopulation is approximately 10–12% (Grant et al., 2004; Johnson, Cohen,Kasen, Skodol, & Oldham, 2008; Samuels, et al., 2002; Torgersen et al.,2001), its association with social dysfunction (Livesley, 2008), and thetendency to engage in inappropriate behavior, including violence(Fountoulakis, Leucht, & Kaprinis, 2008; Reid & Thorne, 2007).

With respect to its association with violence, data indicate thatpersonality disorders provide significant incremental validity in theprediction of violence and recidivism (Hart, Kropp, & Hare, 1988). Forexample, psychopathy has been consistently found to be a reliablepredictor of violent behavior among various populations such asforensic psychiatric patients (Heilbrun et al., 1998) and sexualoffenders (Furr, 1993), as well as in various settings such forensichospitals (Hare, Clark, Grann, & Thornton, 2000; Kroner &Mills, 2001;Pham, Rémy, Dailliet, & Lienard, 1998; Shine & Hobson, 2000;Walters,2003) and after institutional release (Glover, Nicholson, Hemmati,Bernfeld, & Quinsey, 2002; Hemphill, Hare, & Wong, 1998; Kroner &Mills, 2001; Serin, 1996; Serin & Amos, 1995). In fact, a generalconsensus exists that psychopathy is an essential predictive factorwhen conducting risk assessments for institutional problems, violenceand recidivism (Dolan & Doyle, 2000; Gendreau, Goggin, & Smith,2002; Porter, Birt, & Boer, 2001; Salekin, Rogers, & Sewell, 1996).

Nonetheless, controversy surrounded the concept of personalityand personality stability in relation to schizophrenia, and researchershave questioned whether personality, as a structural and functionalentity, is adequate to include in research involving patients withschizophrenia (Camisa et al., 2005). This controversy aside, themajority of research on the relation between personality dimensions,violence and schizophrenia has focused on psychopathy and antisocialpersonality disorders (APD). While these disorders are distinct (Hare& Neumann, 2008) research has often used these terms interchange-ably (e.g., Blackburn & Coid, 1998). Themain difference between thesedisorders is that APD is characterized by the presence of criminalbehavior, and psychopathy is characterized by the presence of a set ofpersonality traits that can lead to criminal behavior (Hare, 1996; Hare

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& Neumann, 2010). With this in mind, and for the purposes of ourreview, studies including APD and psychopathy will both beconsidered in order to evaluate the general role of severe personalitypathology in patients with schizophrenia.

Several studies have shown that personality abnormalities,including personality pathology, are detectable among schizophrenicpatients (Donat, Geczy, & Helmrich, 1992; Newton-Howes, Tyrer,North, & Yang, 2008), present before the onset of the illness (Baum &Walker, 1995; Cuesta, Peralta, & Caro, 1999; Peralta, Cuesta, & Leon,1991), remains relatively stable after illness onset (Kentros et al.,1997), and affects behavioral outcome (Lysaker, Bell, Kaplan, Greig, &Bryson, 1999; Lysaker, Wilt, Plascak-Hallberg, Brenner, & Clements,2003). Prevalence and rate of personality disorders among patientswith schizophrenia are quite robust. For example, in a systematicreview of 20 studies constituting 6345 patients with psychoticdisorders, including schizophrenia, Newton-Howes et al. (2008)found that the comorbidity rate of personality disorders was 39.5%(95%, CI 25.2–55.8%). Moreover, Hodgins, Toupin, and Côté (1996)found that antisocial personality disorders were 5 to 11 times morepresent among patients with schizophrenia compared with age- andgender-matched individuals from the general population, and twoindependent studies have reported elevatedmeasures of psychopathyamong male offenders with schizophrenia (Nolan, Volavka, Mohr, &Czobor, 1999; Rice & Harris, 1995).

Although only few individuals with schizophrenia, among thesegment of offenders qualify as psychopaths (Hodgins et al., 1996), arange of studies converge on the conclusion that psychopathy is anessential predictor of future violence in individualswith schizophrenia(Abushua'leh & Abu-Akel, 2006; Bonta et al., 1998; Dolan & Davies,2006; Fullam & Dolan, 2008; Harris, Rice, & Cormier, 1991; Majoreket al., 2009; Nolan et al., 1999, 2003; Rasmussen, Levander, & Sletvold,1995; Rice & Harris, 1992; Tengström, 2001; Tengström et al., 2004;Tengström, Grann, Långström, & Kullgren, 2000). For example,Tengström and Hodgins (2002) assessed the link between thepsychopathic tendencies of 202 male offenders with a diagnosis ofschizophrenia (81%), schizoaffective or other psychotic disorders andthe risk for violence recidivism. Based on scores obtained on the HarePsychopathy Checklist-Revised (PCL-R), the sample was divided into apsychopathic (score of N26) and a non-psychopathic groups. Theadjusted risk ratio calculated from a Cox regressionwas 4.12, meaningthat psychopaths had four times higher risk for recidivating comparedto the group without psychopathy. In a follow-up study, Tengström etal. (2004) reviewed the files of schizophrenic patientswho underwentpretrial psychiatric assessment in Sweden between 1988 and 1993, asa result of charges involving violent offending. Of the 202 patientsreviewed, 78 met the PCL-R criteria for psychopathy. When looking atthe relationshipbetween convictions and level of psychopathy in thesepatients, the total PCL-R psychopathy scores were highly correlatedwith the number of convictions per year (r=0.62), and moderately,but significantly correlated with the number of convictions for violentcrimes per year (r=0.38). The results also indicate that schizophrenicoffenders with high scores on PCL-R are linked to histories with moresevere violent offending, display more violent offending and engagein violence more often compared to low PCL-R scoring patients withschizophrenia. The study further suggests that the schizophrenicoffenders with psychopathic traits, and early-onset antisocial behavior,appear similar to non-schizophrenic men with psychopathy. Someauthors, however, have expressed concern that PCL-R predictivevalue of future violence is overstated by the inclusion of informationpertaining to past aggressive and criminal behavior (e.g., Ellard, 1988).While it has been argued that removing these items from the PCL-Rwould decreases its predictive value of violence (Hare & Neumann,2005), there is evidence showing that psychopathy based on a checklistexcluding such confounds would continue to have a predictive utility offuture violence and aggression (e.g., Abushua'leh & Abu-Akel, 2006;Cooke, Michie, & Skeem, 2007).

The importance of including personality traits in risk-assessmentof individuals with schizophrenia is further enhanced by the absenceof significant differences in symptoms between violent and non-violent groups (e.g., Fullam & Dolan, 2008; Rasmussen et al., 1995).For example, Rasmussen et al. (1995) found that high scores onpsychopathy contributed most to the discrimination between violentand non-violent individuals with schizophrenia in a maximumsecurity unit. In fact, the authors report thatmore psychotic symptomswere found in the non-violent group than in the violent group.In a later study, Fullam and Dolan (2008) investigated executivefunctioning and violence in a sample of 33 violent and 49 non-violentmale forensic patientswith schizophrenia, and assessed the severity ofsymptoms using the PANSS and psychopathy using the PsychopathyChecklist-Screening Version (PCL-SV). Here, too, there were no sig-nificant differences between the violent and non-violent group on anyof the PANSS symptom scales, except for a positive correlationbetween PANSS excitement scale and rate of violent incidents. Onthe other hand, violent incidents correlated significantly with PCL-SVtotal score, Factor 1, which relates to the emotional and interpersonalaspects of psychopathy, and Factor 2 which relates to the behavioralaspect of psychopathy. Regression analysis revealed that the inter-personal aspect was the most significant predictor of violence, whichsuggests that violent and non-violent forensic patients with schizo-phrenia are best distinguished by their psychopathic profile ratherthan by specific neuropsychological dysfunctions. Thesefindings are inline with the observation that the severe neurocognitive impairmentsfound in disorganized psychotic states contradicts criminal versatility,in that a certain degree of functioning is required to plan and executeviolent offending (Krakowski, Volavka, & Brizer, 1986).

Overall, these findings underscore the relevance of includingpersonality features when assessing risk for future violence amongpatients with schizophrenia. That is not to say that the symptomatol-ogy of patients with schizophrenia do not predict or influence thetendency to engage in delinquent behavior (as we have shown inSection 4.1 above), but rather that among a specific group of patientswith schizophrenia (i.e. psychopathic traits or severe personalitypathology), evidence suggests, that personality features or traits havea higher predictive value in risk assessment evaluations, than dosymptoms or states related to schizophrenia. Consequently, etiolog-ical research must consider the distinctive violent antecedents foundin the heterogeneous group of patients with schizophrenia wheninvestigating factors contributing to violence. In cases where it ispossible, identifying factors, such as personality features, that underlieviolence among patients with schizophrenia and that are unrelatedto psychoses could help debunk the myth that schizophrenia per seinduces violence and consequently attenuate the tendency for socialrejection of that group (Angermeyer & Matschinger, 1996; Link,Phelan, Bresnahan, Stueve, & Pescosolido, 1999; Van Dorn, Swanson,Elbogen, & Swartz, 2005).

4.3. Mentalizing

The ability to infer and comprehend the mental states of self andother, often referred to as mentalizing or Theory of Mind (ToM), hasbeen proposed as an important construct in the understanding ofviolence and delinquent behavior in general (Addy, Shannon, &Brookfield, 2007; Blair et al., 2004, 2006; Covell & Scalora, 2002; Hare,2006; Levinson& Fonagy, 2004). This ability, which is comprised of bothcognitive (i.e., reasoning about beliefs) and affective (i.e., reasoningabout emotions) dimensions, (Abu-Akel, 2003; Baron-Cohen, 1997;Blair, 2005; Brothers & Ring, 1992; Mitchell, 1998) is considered aprerequisite for inter- and intra-relational adjustment, including affectregulatory processes and impulse control (Allen, Fonagy, & Bateman,2008; Baumeister & Heatherton, 1996;Weiss et al., 2006), aswell as theability to empathize and feel guilt (Blair, 2005). More specifically, itis suggested that emotional mental states understanding can reduce

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the propensity to engage in violence (e.g. Eisenberg & Fabes, 1990;Miller & Eisenberg, 1988; Tangney, 1991), function as a potent inhibitorof aggression (Fullam & Dolan, 2006), and that the lack thereof can bea risk factor for violence (Hare, 1991; Murphy, 1998; Shamay-Tsoory,Harari, Aharon-Peretz, & Levkovitz, 2010; Ward, Keenan, & Hudson,2000).

A large body of research now confirms thatmentalizing abilities arecompromised in schizophrenia (Abu-Akel & Abushua'leh, 2004; Allenet al., 2008; Ang & Pridmore, 2009; Bora, Yücel, & Pantelis, 2009a,2009b; Brune, 2005; Fonagy, 2003; Frith, 2004; Harrington, Siegert, &McClure, 2005; Lysaker et al., 2008;Murphy, 2006; Sprong, Schothorst,Vos, Hox, & van Engeland, 2007). More specifically, it has beensuggested that schizophrenia can be understood as a disorder of therepresentation of mental states where, for example, delusions ofpersecution and ideas of reference can be understood in terms of abreakdown in the ability to monitor the thoughts and intentionsof others (Corcoran, Mercer, & Frith, 1995; Frith, 2004; Pickup &Frith, 2001). Based on these findings and the suggested associationbetween mentalizing and violence, Abu-Akel and Abushua'leh (2004)investigated the association between violence and mentalizing abilitiesin patients with schizophrenia, and showed that while the ability tomake empathic inferences (i.e., affective ToM) decreased the likelihoodof violence engagement, demonstrating comprehension of cognitivemental states (i.e., cognitive ToM) increased the possibility for violence.In a more recent study, Majorek et al. (2009) compared a forensic andnon-forensic sample of patients with schizophrenia with a healthycontrol group, in relation to symptomatology, mentalizing abilities andexecutive functioning. Mentalizing skills in this study were assessedusing a picture story sequencing task followed by a questionnairethat addressed the mental states of the cartoon characters. Whilethe forensic and non-forensic groups did not differ in their overallperformance, the forensic outperformed the non-forensic group in thequestionnaire part of the task. This differencewas not due to differencesin premorbid intelligence or executive functioning between thetwo groups. However, when taking into account differences in thepsychopathological profile of the two patients groups, the overallperformance of the forensic groupwas significantly better than the non-forensic group.

Interestingly, both studies report better cognitive mentalizingabilities in the violent than the non-violent group. The association ofintact cognitive mentalizing abilities with increased risk of violencemay appear paradoxical, however. In one respect, this seemingcontradiction is not illogical, given that mentalizing abilities arenecessary for manipulative and deceptive purposes. For example, it ispossible that violence observed among patients with paranoidschizophrenia (Abu-Akel & Abushua'leh, 2004) can be attributed, inaddition to deficits in empathic abilities, to the ability to usementalizingabilities to manipulate and deceive their victims. This is in keepingwithstudies reporting that schizophrenic patients can commit premeditatedviolent crimes (Rice, 1997), which inherently require mentalizingabilities, as well as with reports indicating that lethal or near lethalacts of violence can be associated with intellectually intact psychoticindividuals (Nestor et al., 1995).

To date, research addressing the relation between schizophrenia,violence and mentalization remains sparse. However, available evi-dence suggests that future research may provide valuable insightinto the nature of the psychological processes characterizing violentindividuals with schizophrenia, and research paradigms that incorpo-rate cognitive and affective aspects of mentalizing can be especiallyinformative.

4.4. Substance abuse

The general association of substance abuse with violence has beenwell documented (Fazel, Långström, Hjern, Grann, & Lichtenstein,2009; Grann, Danesh, & Fazel, 2008; Grann & Fazel, 2004; Pernanen &

Heath, 1991), and numerous studies report that substance abuseplays a major role in the occurrence of violence among patients withschizophrenia (Elbogen & Johnson, 2009; Mullen, 1997; Scott et al.,1998; Smith & Hucker, 1994; Soyka et al., 1993; Steadman et al., 1998;Swartz et al., 1998a; Wessely, 1997).

However, considerable uncertainty remains as to whether schizo-phrenia without substance abuse comorbidity is actually associatedwith violence (Brennan et al., 2000; Mullen et al., 2000; Räsänen et al.,1998; Swanson et al., 2000). This association is presumed to beprecipitated by the high prevalence of comorbid substance abuseamong patients with schizophrenia, where rates ranging from 20 to50% have been found in both general and forensic settings (Allebeck,Adamsson, Engström, & Rydberg, 1993; Arndt, Tyrrell, Flaum, &Andreasen, 1992; Blanchard, Brown, Horan, & Sherwood, 2000;Mueser et al., 1990; Rice & Harris, 1995; Soyka et al., 1993; Tengströmet al., 2000). Indeed, high prevalence of violence in patients withcomorbid substance abuse and schizophrenia has been reported acrossvarious epidemiological (Lindqvist & Allebeck, 1990a; Regier et al.,1990) as well as longitudinal prospective studies (Appelbaum et al.,2000; Fazel, Långström, et al., 2009; Hodgins, 1992; Hodgins et al.,1996; Modestin & Ammann, 1995; Monahan et al., 2000; Tengströmet al., 2000).

For example, data suggest that schizophrenic patients withsubstance abuse comorbidity are twice as likely to engage in violentacts (Eronen, Hakola, & Tiihonen, 1996; Lindqvist & Allebeck, 1990a;Swanson et al., 1990) and have higher convictions rates of almostthree to one (40.1% vs. 13.7%) when compared to patients withoutsubstance abuse (Soyka, 1994; Soyka et al., 1993). Moreover, inforensic settings, Rice and Harris (1995) found that 26% of patientswith schizophrenia and comorbid substance abuse where violentoffenders compared to only 7% among patients without substanceabuse. A similar finding was recently reported in a longitudinal studyby Fazel et al. (2009a) where the rates for violent crime amongpatients with schizophrenia with comorbid substance abuse were 3times higher than for patients with schizophrenia, without substanceabuse. Finally, and perhaps one of the most convincing findingspertaining to the effect of substance abuse in patients withschizophrenia is a 26-year follow-up study from an unselected birthcohort in Finland (N=11,017), where individuals with both schizo-phrenia and substance misuse were 25.2 times more likely to commitviolent crimes than healthy individuals (Räsänen et al., 1998).

In all, these findings strongly suggest that the association betweenschizophrenia per se and violence is radically exacerbated in thesepatients in the presence of substance abuse. Thus, risk assessments inforensic settings must consider substance abuse comorbidity inpatients with schizophrenia, and consequently programs designed tolessen the occurrence of future violence should target substance abuse,and not only the symptomatology associated with schizophrenia.

4.5. Demographic factors

Many studies investigating the role of sociodemographic riskfactors for violence in general psychiatric populations (Amore et al.,2008; Modestin, 1998; Rossi et al., 1986; Tardiff & Koenigsberg, 1985)and in patients with schizophrenia (Bonta et al., 1998; Hodgins, 1992;Swanson et al., 1990) reveal that violence is associated with economicdeprivation (Modestin & Ammann, 1996; Monahan, 1993; Swansonet al., 1990; Swanson, Van Dorn, et al., 2008), social living status (e.g.,living with others rather than living alone) (Swanson, Van Dorn, et al.,2008), age where younger individuals are more likely to commitviolent acts (Andrews & Bonta, 1998; Modestin & Ammann, 1996;Monahan, 1997; Swanson et al., 1990), and gender where men aremore likely than women to engage in violence. When compared toage, gender and socioeconomic matched populations, patients withschizophrenia engage in violence earlier (Modestin, 1998; Modestin& Ammann, 1996), and significantly more often than individuals

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without schizophrenia (Hodgins, 1992; Tiihonen et al., 1997). Thesetrends are also evident among women (Hodgins, 1992; Lindqvist &Allebeck, 1990b; Modestin & Ammann, 1995).

5. Treatment approaches to violence in schizophrenia

Introducing the term “treatment” in relation to schizophreniacould very easily bemisunderstood, as it refers to the process of curingschizophrenia. It is not the purpose here to evaluate general treatmentof schizophrenia, but rather to review treatment targeted at amelio-rating risk factors that are thought to induce violence in schizophre-nia. An essential point in this context is that treatment initiativestargeted at reducing aggression and violence should not be inter-twined. Inhibiting and treating aggression do not automaticallyreduce violence and vice versa. Cognitive–behavioral therapy (CBT),as an example, has shown to be effective in reducing anger andaggression in patients suffering from severe mental illness (Chemtob,Novaco, Hamada, & Gross, 1997; Haddock et al., 2009; Haddock,Lowens, Brosnan, Barrowclough, & Novaco, 2004; Renwick, Black,Ramm, & Novaco, 1997) but these studies have not displayed reducedrisk for violence. Albeit aggression and violence are related, andthat the former is probably a precursor of the latter, we would like tounderscore that treatment initiatives targeted at aggression will notbe addressed here.

It has been proposed that risk factors related to gender, age, pasthistory of violence and, to a certain extent, stable traits such aspsychopathy, are less amenable to change and therefore conceived asless applicable for reducing violence risk (Douglas et al., 2009; Skeem&Mulvey, 2001; Steadman et al., 2000). Conversely, other risk factors,such as TCO-symptoms, command hallucinations, mentalizing abili-ties, substance misuse and some personality features, are malleableand therefore pertinent for riskmanagement (Douglas & Skeem, 2005;Heilbrun, 1997; Monahan et al., 2000; Strand, Belfrage, Fransson, &Levander, 1999). Indeed, studies report that neuroleptic treatment hasgenerally resulted in a marked decline in violent incidents (Arango &Bernardo, 2005; Chengappa, Goldstein, Greenwood, John, & Levine,2003; Citrome et al., 2006; Dorevitch, Katz, Zemishlany, Aizenberg, &Weizman, 1999; Garmendia, Sánchez, Azpiroz, Brain, & Simón, 1992;Steinert et al., 2000a; Wilson & Claussen, 1995), and even appearseffective in preventing the occurrence of future violence in schizo-phrenia (Swanson, Swartz, Elbogen, & Van Dorn, 2004; Taylor et al.,1996). Specifically, psychopathological causes related to violenceamong patients with schizophrenia have proved to be amenable toeffective antipsychotic treatment (Buckley et al., 1995; Steinert,Sippach, & Gebhardt, 2000), especially to second-generation antipsy-chotics such as olanzapine, clozapine, risperidone, quetiapine, andziprasidone (Buckley, 1999; Buckley et al., 1995; Citrome, Krakowski,Greenberg, Andrade, & Volavka, 2001; Swanson et al., 2004; Tayloret al., 1996; Volavka, 1999; Volavka et al., 2002), although somecontroversy exists as to the superiority of clozapine compared to theeffects of olanzapine and risperidone on reducing violence (Bitter,Czobor, Dossenbach, & Volavka, 2005; Citrome, Valovka, et al., 2001;Krakowski, Czobor, Citrome, Bark, & Cooper, 2006; Krakowski, Czobor,& Nolan, 2008; Volavka & Citrome, 2008). However, owing to theuncertainty regarding the interaction of the multiple risk factors forviolence in individuals with schizophrenia, some controversy existsas to whether antipsychotic medications can reduce violence ingeneral or only when such behavior is related directly to psychosis(Swanson, Swartz, et al., 2008). More specifically, Swanson, Swartz,et al. (2008) contend that antipsychotic treatment applied as generalviolence risk management, only seemed effective in patients were arelation between violence and symptomatology existed—no reductionin violence was observed in the absence of such relationship.

Given the relative success of medication in abating the occurrenceof violence in schizophrenia, several studies emphasize the importanceof medication adherence to violence risk management (Swanson,

Swartz, et al., 2008; Swartz, Van Dorn, et al., 1998b), and there arereports linking higher violence rates and arrest (Ascher-Svanum, Zhu,Faries, Lacro, & Dolder, 2006) as well as an increase in violence severity(Alia-Klein, O'Rourke, Goldstein, & Malaspina, 2007) with non-adherence to medical treatment. Moreover, specialized forensiccommunity treatment programs, which incorporate both medical andpsychosocial interventions, haveproved effective inpreventingviolenceamong patients with schizophrenia in the United States (Heilbrun &Peters, 2000; Wiederanders, 1992; Wiederanders, Bromley, & Choate,1997;Wiederanders & Choate, 1994)Germany (Muller-Isberner, 1996),and Canada (Hodgins, Lapalme, & Toupin, 1999; Wilson, Tien, & Eaves,1995).

Notwithstanding the promise these therapeutic interventions holdfor the abatement of violence, the development of psychotherapeuticinterventions for patients with psychotic symptoms displaying violenceremains sparse (Haddock et al., 2009), and the effect of suchinterventions on psychosis and violence are often studied separately.Moreover, current risk assessment tools often lead tomiscategorizationof patients as being at high risk for violence when in fact they are not(Large, Ryan, Singh, Paton, & Nielssen, 2011).

In order to treat and prevent violence in individuals withschizophrenia, it is essential to adopt a developmental framework,where continual interaction of biological, psychological and socialfactors are acknowledged as interdependent aspects of whatconstitutes violence in schizophrenia. As presented in this review,violent patients with schizophrenia are a heterogeneous group, withrather different etiological and developmental trajectories whereparticular individual characteristics interact with both the immediateand the larger social environments to determine emotions, cognitionsand behavior, including violence. Hence, what seems to be similaroutcome in patients with schizophrenia (i.e. violence), is probablycaused by the distinct idiosyncratic developmental trajectories, andtherefore required as a referential background, when structuringintervention targeted at preventing violence. Moreover, a majorchallenge facing the success of these interventions, however, is thelimitations inherent in the mental health system to detect and treatindividuals with first-episode psychosis amongst whom the riskfor violence is exceptionally high (Large & Nielsen, 2011). Thisproposition introduces new perspectives into the realm of treatmentof violence in schizophrenia, since it delineates a prevention-model,as opposed to the current post-hoc interventions targeted at reducingviolence in schizophrenia.

Thus, any intervention (medical or psychosocial) aiming atdecreasing violence in patients with schizophrenia, must consider thefollowing: 1) Symptomatology, i.e. the interaction of positive andnegative symptoms, and presence of specific constellations of symp-toms such as TCO symptoms, persecutory ideation and commandhallucinations. In this context, detection and treatment of individualsduring the first-episode psychosis phase is paramount; 2) trait-relatedpathology such as personality disorders and psychopathic traits;3) functionality of social cognitive skills such as mentalizing; 4) sub-stance abuse, including substancemisuse onset, and other axis-I relatedillnesses; 5) patient's environment, that is whether the patient intreatment is incarcerated, inpatient in a hospital or living in thecommunity; 6) history of delinquent behavior as well as the occurrenceof violent behavior before and/or after illness onset; and finally7) demographic information such as age and gender.

6. Closing remarks

The main objective of this review was to evaluate whetherschizophrenia enhances violence compared to people without schizo-phrenia. However, schizophrenia exhibits a heterogenic group withdifferences in illness trajectories and symptomatology which, in turn,makes it very difficult to conclude if schizophrenia per se contributesto violence, and further questions the straightforward relationship

720 S. Bo et al. / Clinical Psychology Review 31 (2011) 711–726

between schizophrenia and violence.What is probablymore adequateis to investigate which specific constellations of symptoms and/orfactors that are related to or comorbid with schizophrenia areassociated with risk for violence.

Our state of knowledge suggests that the occurrence of violence inschizophrenia is associated with a number of sociodemographicvariables that include, but not limited to, age, gender and economicand social living status. Similar to offenders and violent individualsin the general public, violence in schizophrenia is predominantlyperpetrated by young, male individuals of disadvantageous socioeco-nomic status. Within this context, and as illustrated in Fig. 1, weidentify several additional key factors, which contribute to theoccurrence of violence in schizophrenia. These include psychoticsymptoms, particularly during first-episode psychosis, psychopathyand personality disorders, mentalizing abilities, and substance abuse.

At the level of psychotic symptoms studies suggest that positivesymptoms are significantly more strongly related to violence thannegative symptoms. Hallucinations, delusions and threat/control-override symptoms are all associated with violence, but their relativecontribution to violence is still under debate. This association appearsstrongest in untreated individuals during first-episode psychosis. Byinvestigating the link between violence and specific constellations ofsymptoms, particularly during first episode psychosis, instead of thebroad diagnosis of schizophrenia, however, potential causal explana-tions can emerge. Albeit related to schizophrenia, hallucinations,delusions and disorganization symptoms, are symptoms that consti-tute other illnesses as well and can be experienced by members of thegeneral population (Mojtabai, 2006). Hence specifying a relationshipbetween these symptoms and violence, is not to say that schizophre-nia contributes to violence, rather, that a specific constellation ofsymptoms that are also present in schizophrenia are associated withviolence. However, a methodological weakness that is apparent inmost studies addressing the relationship between psychosis andviolence (particularly those of retrospective design) is the inability tospecify the symptomatic profiles present at the time of committing aviolent act. This is vital for evaluating formulations that posits a causalexplanation between the presence of psychoses and the occurrenceof violence and should be addressed in future research.

Moreover, given that untreated psychotic conditions representan increased risk for committing violent acts, earlier detection andtreatment of psychosis is paramount.

Fig. 1. Main factors contributing to the occurrence of violence in schizophrenia.

With respect to the relationship between psychopathy and per-sonality disorders and violence in schizophrenia two importantimplications can be observed. First, it is possible to detect andmeasure personality features, i.e. personality pathology, in patientswith schizophrenia, and second, it is necessary to include personalitymeasurements when assessing risk for violence among patients withschizophrenia. This is particularly important when assessing therisk for violent recidivism. A combination of various measurementswhen conducting risk assessment could improve the accuracy ofrisk assessment in patients with schizophrenia, and help constructactuarial risk scales that can be validated. Furthermore, a commonfinding is that psychopaths demand specific treatment-programs,and that inappropriate treatment approaches is contraindicative to re-socialization of offenders, and in extreme cases deteriorates theircondition. Obtaining information about potential psychopathy traitsin patients is thus crucial for treatment-planning.

Another important factor, independent of the diagnosis of schizo-phrenia, is substance abuse. It is clear that substance abuse in patientswith schizophrenia elevates the risk rate for violence significantly. Thisrelationship underscores the necessity of addressing substance misusein research as well as in clinical practice targeting the prevention ofviolence in patientswith schizophrenia. This is furtherwarranted by thefact that a significant number of patients suffering from schizophreniaare also struggling with substance misuse comorbidity.

Recent studies also suggest that impairments in the ability tounderstand and infer the intention of oneself and others (i.e.,mentalizing), which is a frequent consequence of schizophrenia,appears to impinge on one's tendency to commit violent acts. Althoughthe number of studies conducted on this subject in relation toschizophrenia is limited, the findings reported here indicate thatviolence committed by individuals with schizophrenia is associatedwith intact “cognitive” mentalizing abilities in combination withdeficient “affective” mentalizing abilities. While it is premature toassess the reliability of this relationship, it is a profitable direction topursue in that such research has the potential to point out psychologicalmechanisms that could explain violence in schizophrenia, and in doingso complement research that relies on behavioral observations.

However, as noted above, violent patients with schizophreniaconstitute a heterogeneous population with multiple etiologies anddissimilar developmental trajectories, exhibiting diverse patternsof violence. It is therefore necessary to develop a typology wherespecific casual mechanisms and treatment programs are specificallytailored to each offender type. An emergent finding is that positivepsychotic symptoms appear not to influence the level of adult violentoffending with early-onset antisocial behavior but, in contrast, havean effect on those with no reported history of childhood antisocialbehavior. This suggests that violence associated with schizophreniahas at least two different developmental trajectories: one associatedwith premorbid antisocial conduct problems, and another relatedwith psychotic symptoms. Fig. 2 presents a schematic representationof the occurrence of violence in schizophrenia as precipitated by thesetwo developmental trajectories.

In the first group, both psychopathy and antisocial personalitytraits represent essential predictive variables that explain the relationbetween schizophrenia and violence over and above psychoticsymptoms and substance abuse. Individuals subscribing to thisgroup appear to be capable of instrumental (i.e., premeditated,planned) violence which is characterized by the presence of relativelyintact cognitive mentalizing and largely compromised emotionalmentalizing. Psychotic symptoms may be present in this group,but the amelioration of these symptoms may have little effect onattenuating the likelihood for violence. In the second group, theoccurrence of violence seems to be associated with the presence ofpositive psychotic symptoms and overall compromised mentalizingabilities. Violent acts committed by members of this group are oftenreactive, and can be exacerbated with substance-abuse comorbidity

Secondary concernsSubstance abuseDelinquent personality featuresMentalizing disabilities

Primary explanationPsychopathic traitsAntisocial personality disorder

No antisocial behavior prior to illness onset

Antisocial behavior prior to illness onset

Violence in Schizophrenia

Secondary concernsPositive psychotic symptomsSubstance abuseMentalizing disabilities

Target interventionPersonality features related to psychopathy

Treatment methodNot availible

Primary explanationPositive psychotic symptoms:

- TCO- Command hallucinations- Persecutory ideation- Delusions/hallucinations with

threatening content

Target interventionPositive psychotic symptomsSubstance abuse

Treatment methodCognitive behavioral therapy (CBT)

Fig. 2. The occurrence of violence in schizophrenia as a consequence of two developmental trajectories.

721S. Bo et al. / Clinical Psychology Review 31 (2011) 711–726

(Walsh et al., 2002). Phramacotherapeutic and behavioral interven-tions may be effective in curbing the occurrence of violence in thisgroup.

In all, a number of factors which include specific constellationsof psychotic symptoms, particularly during first episode psychosis,personality features, mentalizing abilities, substance abuse andvarious demographic variables appear to affect the direction and/orstrength of the association between schizophrenia and violence. Thesefactors should be considered in research, clinical practice and riskassessment of potentially dangerous individuals with schizophrenia.It should be noted that while many epidemiological, cohort andprospective studies lead to believe that there is a significantrelationship between schizophrenia and violence, only a smallproportion of societal violence is accounted for by patients withschizophrenia. In fact, results indicate that 99.97% of those withschizophrenia would not commit serious violence in a given year(Walsh et al., 2002). Furthermore, these studies have “only” been ableto detect a relation, but not conclude on the causal direction of therelationship. Probably the most important finding that emerges fromthis review is the extent to which the strength of the associationbetween violence and schizophrenia differ as a function of thesevariables. Indeed, if generalizing from one group of research, theconclusion would be that schizophrenia is inversely related toviolence, and from another set, that schizophrenia is a very strong

correlate of violence. This variation in strength of association, asdisplayed throughout this paper, suggest that research needs to payconsiderable attention to study-design and methodologies employedin investigating hypotheses about the association between schizo-phrenia and violence.

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