Aggressive behaviour in schizophrenia: role of state versus trait factors

Ž .Psychiatry Research 72 1997 41]50

Aggressive behaviour in schizophrenia: role of state versustrait factors

Peter Cheunga,U , Isaac Schweitzerb, Kathleen Crowleyb, Virginia Tuckwellb

aAcademic Unit in Rehabilitation Psychiatry, Department of Psychiatry, Uni®ersity of Melbourne, 131 Wood Street, Preston,3072, Victoria, Australia

bProfessional Unit, Department of Psychiatry, Uni®ersity of Melbourne, Melbourne Clinic, 130 Church Street, Richmond,3121, Victoria, Australia

Received 16 July 1996; revised 9 June 1997; accepted 20 June 1997

Abstract

The objective of this article was to elucidate the relative importance of state vs. trait factors in determiningaggressive behaviour in schizophrenia. Thirty-one aggressive schizophrenia patients in rehabilitation wards werecompared with 31 matched non-aggressive patients with respect to their psychopathology, phenomenologies ofhallucinations and delusions, neuroleptic motor side effects, history of aggression and personality traits. Significantdifferences between the two groups were found in relation to psychopathology, affective responses tohallucinationsrdelusions, history of aggression and personality traits, but there were no significant differencesregarding neuroleptic motor side effects. The effects of history of aggression as well as personality traits wereindependent of and similar to the total level of psychopathology, but were much smaller when compared to those ofnegative affective responses to hallucinationsrdelusions. Q 1997 Elsevier Science Ireland Ltd.

Keywords: Aggressive behaviour; Schizophrenia; Hallucinations; Delusions; Personality; History of aggression

1. Introduction

Even though most schizophrenia patients arenot violent, it is a well-established finding that

U Corresponding author. Tel.: q61 3 94718165; fax: q61 394718174.

they do have a higher rate of aggressive be-haviour when compared to the general populationŽMonahan, 1993; Torrey, 1994; Wessely et al.,

.1994 . Among psychiatric patients, those who haveaggressive behaviour are more likely to have a

Žprimary diagnosis of schizophrenia Lee et al.,.1989; Noble and Rodger, 1989 . Many previous

studies on the correlates of aggressive behaviour

0165-1781r97r$17.00 Q 1997 Elsevier Science Ireland Ltd. All rights reserved.Ž .P I I S 0 1 6 5 - 1 7 8 1 9 7 0 0 0 9 0 - 5

( )P. Cheung et al. r Psychiatry Research 72 1997 41]5042

in schizophrenia have been done. It has beenfound that schizophrenia patients are likely to beaggressive only when they are actively sympto-

Žmatic Hafner and Boker, 1982; Taylor, 1985;.Link et al., 1992 . There is some evidence that

akathisia, a motor side effect of neuroleptics, isassociated with aggressive behaviour in

Žschizophrenia Herrera et al., 1988; Crowner et.al., 1990 . There is a growing body of evidence

that substance abuse increases the risk of aggres-Žsion among schizophrenia patients Lindqvist and

Allebeck, 1989; Swanson et al., 1990; Cuffel et al.,.1994 . A past history of aggression, as in the case

of the general population, is a good predictor offuture aggression among psychiatric patientsŽKroll and Mackenzie, 1983; Davis and Baxter,

.1988 . There is some preliminary evidence thatpersonality traits are important in determining

Žaggressive behaviour in schizophrenia Plutchik et. Ž .al., 1989 . Hare and Hart 1993 reviewed the

literature and concluded that psychopathic traitspredict violence even among those with psychosis.However, they also cautioned that there was stilla lack of solid empirical data and that the interac-tive effect of psychopathy and mental disorder oncriminal behaviour had not been studied.

The correlates of aggressive behaviour inŽ .schizophrenia can be grouped into: 1 statercon-

textual factors including psychopathology andŽ .neuroleptic motor side effects; and 2 traitrdis-

positional factors including personality traits andpremorbid history of aggression. Given that ag-gressive behaviour is often regarded as the resultof an interplay of state vs. trait factors, it wouldbe important to determine the relative impor-tance of such factors in determining aggressivebehaviour in schizophrenia. Also, whilst both stateand trait factors are relevant to risk assessment,only statercontextual factors are relevant to riskmanagement as clinicians cannot changetraitrdispositional factors, such as gender and

Ž .personality Steadman et al., 1993 . To ourknowledge, there is only one previous study whichspecifically addressed the issue of state vs. trait

Ž .factors. Krakowski et al. 1989 compared a per-Žsistently violent group those whose violence per-

sisted beyond 10 days since transfer to a special-.ized unit for aggressive patients , a transiently

Žviolent group those whose violence subsidedwithin 10 days after transfer to the specialized

.unit and a non-violent group. They found thatthe persistently violent group had significantlymore neurological abnormalities and a more dis-turbed family background than the transientlyviolent group and the non-violent group. Theysuggested that neurological abnormalities anddisturbed family background could predispose tothe more persistent type of violence, but not tothe transient type. This study had a heteroge-neous population, and patients with organic braindamage, which by itself could be associated withaggression, were not excluded. Also, the level ofpsychopathology was not described so that it wasunclear, apart from the two predisposing vari-ables mentioned, whether violence persisted be-cause of persistent psychopathology. This studyaims to clarify the relative importance ofstatersituational vs. traitrdispositional factors indetermining aggressive behaviour in schizophre-nia.

2. Methods

We used the Staff Observation Aggression ScaleŽ .SOAS; Palmstierna and Wistedt, 1987 , an in-strument with established reliability and validity,to prospectively study the prevalence and featuresof aggressive behaviour of all 220 inpatients withinthe Rehabilitation Program of North Eastern

Ž .Metropolitan Psychiatric Services NEMPS dur-Ž .ing an 8-week period Cheung et al., 1996, 1997a .

2.1. Subject Selection

Ž .Subjects were selected from patients ns220who were studied during the 8-week survey andstill remained in the Rehabilitation Program,NEMPS, at the time of this study. All those

Ž .patients who were observed using the SOAS tohave two or more physical aggressive incidentsduring the survey were screened to select subjectsmeeting the following criteria:

1. continue to have on average at least oneincident of physical aggression per month

( )P. Cheung et al. r Psychiatry Research 72 1997 41]50 43

during the time interval between the 8-weekobservation period and this study;

2. have stable medications during the previous 2months;

3. have at least one current positive symptom;4. do not have a current diagnosis of substance

abuse, a history of significant head injury, ormoderate to severe intellectual impairment;

5. have an adequate command of English;6. give informed written consent to participate

in the study; and7. have a clinical diagnosis of schizophrenia or

schizo-affective disorder confirmed using theStructured Clinical Interview for DSM-III-RŽ .SCID-P; Spitzer et al., 1990 .

Selection criteria 1]5 were assessed by reviewof the patient’s medical record and discussionwith the treating psychiatrist. Potential subjectswere administered a urine screen for illicit drugsand those who had positive results were excludedfrom the study. Thirty-one such subjects could beidentified and they formed the aggressive group.

Another 31 subjects, matched for age, gender,age at first psychiatric admission and duration ofcurrent admission with the aggressive group, were

Žselected out of patients who were observed using.the SOAS to have no aggressive incidents at all

during and subsequent to the 8-week survey.These subjects had to meet all the other selectioncriteria met by the aggressive group. They formedthe non-aggressive group.

2.2. Procedure

The background information of age, gender,age at onset of schizophrenia, age at the firstpsychiatric hospital admission, duration of cur-

Žrent admission, history of aggression threats ofviolence, destruction of property, suicide attempt

.and physical assault before onset of schizophre-nia, during and in between previous admissions,was collected at a structured interview. Additio-nal information was sought from the subject’smedical record, family membersrcarers and treat-ing psychiatrist whenever necessary. History ofaggression was rated using the Modified Overt

Ž .Aggression Scale MOAS; Kay et al., 1988 . The

current dose of neuroleptic was calculated interms of chlorpromazine equivalents. The typesand doses of all current psychotropic medicationswere also recorded. The following were assessedfor each subject:

2.2.1. PsychopathologyThe Positive and Negative Syndrome Scale

Ž .PANSS; Kay et al., 1987 was used to assesspositive symptoms, negative symptoms and theassociated mood and behavioural disturbances.

Those who were found by the PANSS to expe-rience auditory hallucinations in the previousmonth were administered a series of phenomeno-logical items including the tone, volume, fre-quency, degree of reality, emotional responsesand coping mechanisms associated with the hallu-cinations, taken from the MHRI Unusual Percep-

Žtions Schedule MUPS; Carter and Copolov,.1993 . It is a semi-structured interview having

high levels of inter-rater reliability with meanŽkappa ranging from 0.81 to 0.98 Carter et al.,

.1995 .Those who are found by the PANSS to have

delusions in the previous month were asked aseries of questions relating to the phenomenologyof the principal belief } the delusion subjectivelyregarded as the most important. These questionswere contained in the Maudsley Assessment of

Ž .Delusions Schedule MADS; Taylor et al., 1994Ž .and were used by Buchanan et al. 1993 in their

study of the phenomenological characteristics ofthose delusions associated with action. Thesequestions included the degrees of conviction, in-sight, preoccupation and systematisation of, theemotional responses to and factors maintainingthe principal delusional belief.

2.2.2. Motor side effects of neurolepticsAkathisia was rated using the Barnes Akathisia

Ž .Scale Barnes, 1989 , drug-induced Parkinsonismwas assessed on the 10-item scale of Simpson and

Ž .Angus 1970 and tardive dyskinesia was assessedusing the Abnormal Involuntary Movement ScaleŽ .Lane et al., 1985 .

2.2.3. PersonalityAll subjects completed the following self-report


Žtests: the Impulsivity Scale Plutchik and van.Praag, 1989 which assesses the tendency to en-

gage in impulsive, spur of the moment behaviour.The Hostility and Direction of Hostility Ques-

Ž .tionnaire Caine et al., 1967 was used to assessboth the states and the traits of irritability andhostility. It has five subscales: the urge to act out

Ž . Ž .hostility AH , criticism of others CO , projectedŽ . Ž .delusional i.e. paranoid hostility PH , self criti-

Ž . Ž .cism SC and guilt G . AH, CO and PH weretests of extrapunitiveness whilst SC and G weretests of intropunitiveness. Hostility is the simplesum of all five tests. Direction of Hostility is the

Žsum of the intropunitive tests with SC counted.twice over less the sum of the extrapunitive tests.

The Minnesota Multiphasic Personality InventoryŽ .MMPI; Hathaway and McKinley, 1967 Psycho-

Ž .pathic Deviance PD subscale was used to assessantisocial traits. The research nurse was presentwith each subject during these tests and, if re-quested, would read the questions and record thesubject’s answers. A random sample of 20 sub-jects were requested to complete the inventories

Ž .twice with a 2-week interval to check theirtest]retest reliabilities.

2.3. Data analysis

The aggressive and non-aggressive groups werecompared using Student’s t-tests for continuousvariables and x 2 tests with Yates’ Correction as

Žwell as Fisher’s exact tests when the cell numbers.became too small for x statistic to be accurate

for categorical variables. Non-parametric testswere used, where the data were not normallydistributed. Data analysis was performed usingSPSS for Windows, Release 6.1.

3. Results

3.1. Characteristics of subjects

There were 29 males and 11 females in eachŽ .group. The mean "S.D. age of the aggressive

Ž .group was 37.7 "7.5 years whilst that of theŽ .non-aggressive group was 37.4 "4.8 years. The

Ž .mean "S.D. age at first psychiatric admission ofŽ .the aggressive group was 18.3 "3 years whilst

Ž .that of the non-aggressive group was 20.0 "4.4

Ž .years. The mean "S.D. length of current admis-Ž .sion was 9.8 "8.7 years whilst that of the non-

Ž .aggressive group was 6.3 "9.4 years. The twogroups did not differ significantly in any of theseparameters.

3.2. Psychopathology

The detailed results are published elsewhereŽ .Cheung et al., 1997b . Briefly, the aggressivegroup had significantly higher positive symptom,negative symptom, general psychopathology andtotal PANSS scores than the non-aggressivegroup. Factor analyses showed that the two groupscould be distinguished by three sets of symptoms:Ž .1 symptoms with verbal andror physical aggres-

Ž .sion as part of their definition; 2 symptomsŽ .suggesting frontal lobe impairment; and 3 ex-

citement.

3.3. Phenomenologies of hallucinations anddelusions

The detailed results will be published else-where. The aggressive group were significantlymore likely to experience negative emotions, toneand content related to their voices than the non-aggressive group, whilst the non-aggressive groupwere more likely to experience positive emotions,tone and content related to their voices. Thenon-aggressive group were significantly morelikely to report success in coping with their voices.There was no association between command hal-lucinations and aggressive behaviour. The aggres-sive group were more likely to hold persecutorydelusional beliefs than the non-aggressive group,while the non-aggressive group were more likelyto hold grandiose delusions than the aggressivegroup. The aggressive group were also more likelyto report that the delusions made them feel an-gry, while the non-aggressive group were morelikely to report that the delusion made them feelelated.

3.4. Neuroleptic motor side effects

The detailed results are published elsewhereŽ .Cheung et al., 1997c . Briefly, the aggressivegroup had significantly more severe extrapyrami-


dal side effects than the non-aggressive group,but this association disappeared when psy-chopathology was controlled for. The aggressivegroup had a non-significant increase in akathisiawhen compared to the non-aggressive group. Thetwo groups did not differ in the severity of tardivedyskinesia.

3.5. Medications

The aggressive group had a higher mean dailydose of neuroleptic in chlorpromazine equivalentsŽ .1150"845 mg than the non-aggressive groupŽ .890"553 mg , but the difference was not statis-tically significant. There were no significant dif-ferences between the two groups regarding theproportion of patients who were on anticholiner-gic medications and atypical neuroleptics.

3.6. Personality traits

The test]retest reliability of the ICS was rsŽ . Ž .0.56 P-0.05 , HDHQ was rs0.92 P-0.001

Ž .and MMPI PD was rs0.60 P-0.05 . The inter-nal consistency of ICS was as0.7, HDHQ wasas0.91 and MMPI PD was as0.74.

Table 1 shows that the aggressive group hadsignificantly higher mean HDHQ and MMPI PDscores than the non-aggressive group. The formeralso had significantly higher mean HDHQ sub-scale scores and Direction of Hostility scores.However, the two groups were similar in theirICS scores. The ICS scores correlated signifi-

Žcantly with both the HDHQ scores rs0.58, P-. Ž0.001 and the MMPI PD scores rs0.38, P-.0.01 . The HDHQ and MMPI PD scores were

Žalso significantly correlated with each other rs.0.67, P-0.001 .

3.7. History of aggression

Table 2 shows the aggressive group, when com-pared to the non-aggressive group, had signifi-cantly higher MOAS scores across all three peri-ods studied } before onset of schizophrenia,during previous admissions and in betweenadmissions. They also had significantly higherMOAS subscale scores across all three periods,except for aggression towards self which was simi-lar between the two groups across all three peri-ods.

Repeated measures ANOVA showed that,

Table 1Comparison of personality inventory scores between aggressive and non-aggressive groups

Aggressive group Non-aggressive tŽ . Ž .ns31 group ns31

Mean S.D. Mean S.D.

UUUHDHQ 29.0 8.9 19.7 9.3 4.1UUUAH 6.5 2.4 4.2 2.5 3.8UUCO 6.9 2.5 5.0 2.9 2.7UUPH 5.1 2.5 2.9 2.3 3.6USC 6.4 2.5 4.8 2.7 2.4UUG 4.0 2.0 2.5 2.3 2.8UDirection of hostility 8.0 5.1 4.8 5.6 2.3UUMMPI PD 26.3 6.4 20.9 5.7 3.4

ICS 33.2 6.9 31.5 6.3 1.0 N.S.U P-values-0.05.UU P-values-0.001.UUU P-values-0.0001.


Table 2Ž .Comparison of history of aggression MOAS scores between aggressive and non-aggressive groups

Aggressive group Non-aggressive group tŽ . Ž .ns31 ns31

Mean S.D. Mean S.D.

Before onset of schizophreniaUUVerbal aggression 1.0 1.2 0.3 0.4 3.4

UUAggression against property 0.9 1.2 0.2 0.5 3.3Aggression against self 0.1 0.5 0.4 1.2 1.2 NS

UUAggression against people 0.9 1.1 0.2 0.6 3.1UTotal aggression 6.7 7.7 2.4 5.6 2.5

Ž .During previous admissions inpatientUUUVerbal aggression 3.2 0.9 1.2 1.1 7.7UUUAggression against property 2.5 1.2 1.1 1.4 4.4

Aggression against self 1.6 1.5 1.0 1.7 1.4 NSUUUAggression against people 2.8 0.7 0.7 1.0 9.3UUUTotal aggression 24.1 7.3 9.1 7.4 8.1

Ž .Between previous admissions outpatientUUUVerbal aggression 3.0 0.9 1.5 1.3 5.0UAggression against property 2.3 1.5 1.4 1.6 2.3

Aggression against self 1.8 1.8 1.4 1.9 0.7 NSUUAggression against people 2.8 1.0 1.5 1.5 3.6

Total aggression 24.2 8.5 14.8 10.5 3.7UU

U P-values-0.05.UU P-values-0.01.UUU P-values-0.001.

within the aggressive group, the levels of aggres-sion during and between previous admissions weresimilar, but both were significantly higher than

Žthose before the onset of schizophrenia Fs60.9,.d.f.s60, P-0.001 .

3.8. Personality traitsrhistory of aggression ®s.PANSS

The effects of hostility, antisocial traits, historyŽ .of aggression MOAS scores after controlling for

Ž .schizophrenia symptom PANSS scores were cal-culated using logistic regression analyses with ag-gressive grouping as the dependent variable andHDHQ, MMPI PD, MOAS and total PANSSscores as independent variables. The results areshown in Table 3. The effects of HDHQ, MMPI

ŽPD and MOAS remained significant except for.history of premorbid aggression where Ps0.90 ,

after controlling for total PANSS scores and weresimilar in size to the latter.

3.9. Personality traitsrhistory of aggression ®s.negati®e affect associated with hallucinationsrdelusions

Among those who experienced auditory halluci-nations, the effects of hostility, antisocial traits,and history of aggression scores controlling for

Ž .sad affect in response to auditory hallucinationswere calculated using logistic regression analyseswith aggressive grouping as the dependent vari-able and HDHQ, MMPI PD and MOAS scoresand sad affect as independent variables. The re-sults are shown in Table 4. The effects of HDHQ,MMPI PD and MOAS all remained significantŽexcept for history of premorbid aggression where

.Ps0.09 after controlling for sad affect, but weremuch smaller in size when compared to the latter.Among those who held delusional beliefs, similarlogistic regression analyses were performed con-

Žtrolling for angry affect in response to delusional


Table 3The effects of hostility and antisocial traits and history of

Ž .aggression MOAS scores after controlling for schizophreniaŽ .symptom PANSS scores

Odds ratio 95% C.I.Ž .ns62

UHDHQ 1.09 0.85]1.10UUPANSS 1.15 1.05]1.23UMMPI PD 1.12 0.79]1.14UUPANSS 1.24 1.11]1.43Ž .MOAS score before 1.11 Ps0.09 1.02]1.25

onset of schizophreniaUUPANSS 1.14 1.04]1.23UUMOAS during 1.25 1.09]1.43

previous admissionUPANSS 1.14 1.03]1.25UMOAS between 1.10 1.01]1.19

previous admissionsUUPANSS 1.24 1.09]1.43

U P-0.05, UU P-0.01.

.beliefs . The results are shown in Table 5. Theeffects of HDHQ, MMPI PD and MOAS all

Žremained significant except for history of pre-.morbid aggression where Ps0.73 after con-

trolling for angry affect, but were much smaller insize when compared to the latter.

4. Discussion

Even though both the HDHQ and MMPI PDhave been used in patients with schizophrenia in

Žprevious studies e.g. Rangaswami, 1982; Plutchik.et al., 1989 , concern has been expressed about

the use of self-report instruments in determiningpersonality traits among schizophrenia patients,in particular those with active positive symptoma-tology. However, our results show that these twoinstruments have satisfactory internal consistencyand test]retest reliability when used among oursubjects who all had active positive symptoma-tology. Another methodological concern is thatthe nature of abnormal personality traits found inschizophrenia remains unclear. It may reflect theimpact of schizophrenia on normal premorbid

Ž .personality DiLalla and Gottesman, 1995 , but itmay also be genuine premorbid personality traits.

Table 4The effects of hostility and antisocial traits and history ofaggression scores after controlling for sad affect in response tohallucinations

Odds ratio 95% C.I.Ž .ns38

UHDHQ 1.14 1.01]1.28Ž .Sad affect 2.71 Ps0.07 0.82]8.94

UMMPI PD 1.18 1.02]1.35USad affect 3.35 0.94]11.94Ž .MOAS before 1.19 Ps0.09 0.97]1.44

onset schiz.USad affect 3.05 0.91]9.50UUMOAS during 1.33 1.11]1.60

previous adm.UUSad affect 3.70 2.69]6.96UUMOAS between 1.22 0.95]1.39

previous admissionsUSad affect 4.85 1.19]19.89

U P-0.05, UU P-0.01.

Both the mean HDHQ and MMPI PD scoreswere significantly higher among the aggressivegroup than the non-aggressive group, supportingour hypothesis that hostility and antisocial traitsplay a part in determining aggressive behaviour inschizophrenia. Since it has been suggested that

Table 5The effects of hostility and antisocial traits and history ofaggression scores after controlling for angry affect in responseto delusions

Odds ratio 95% C.I.

UHDHQ 1.14 1.01]1.19UUAngry affect 3.60 1.62]8.00UMMPI PD 1.14 0.98]1.30UUAngry affect 4.14 1.85]9.21Ž .MOAS before 1.02 Ps0.73 0.92]1.13

onset schiz.UUUAngry affect 4.58 2.05]10.18UUMOAS during 1.35 1.11]1.49

prev. adm.UUAngry affect 5.24 1.55]17.8UMOAS between 1.12 1.14]3.35

prev. adm.UUAngry affect 3.73 1.65]8.50

U P-0.05, UU P-0.01, UUU P-0.001.


even though intropunitiveness and extrapunitive-ness scores are related, they should be treated as

Ž .distinct concepts Arrindell et al., 1984 , the subs-cale scores of the HDHQ were compared betweenthe aggressive and non-aggressive groups. In bothgroups, the mean extrapunitiveness scores werehigher than intropunitiveness scores in keepingwith the findings in schizophrenia in generalŽ .Tsiantis et al., 1981 . There was thus also asignificant difference between the two groups inthe direction of hostility scores.

The explanation for our unexpected failure tofind a difference on the measure of impulsivityŽ .ICS between the aggressive and non-aggressivegroups is unclear at this stage. The ICS, similar tothe HDHQ and MMPI PD, has satisfactory inter-nal and test]retest reliabilities when used amongour subjects. It was also found to have significantcorrelations with both the HDHQ and MMPIPD, suggesting that the ICS was assessing person-ality constructs related to HDHQ and MMPI PD.The ICS is a relatively new instrument and eventhough it has been used among patients with

Žschizophrenia Apter et al., 1990; Kotler et al.,.1993 , the validity of the instrument when used

among the latter in comparison to other diagnos-tic groups has not been clarified. Further researchon the use of the ICS in schizophrenia appearswarranted.

We used the MOAS to produce historical rat-ings of aggression. Even though itsuse has beenfound to be both reliable and valid for short-termobservation, i.e. 1]2 weeks, its psychometricproperties in assessing life-time history of aggres-sion were unknown. Our findings suggest thismeasure has criterion validity as there were sig-nificant differences between the aggressive andnon-aggressive subjects in relation to all indicesof history of aggression except for history of ag-

Ž .gression towards self. Kay et al. 1988 , using asimilar method to assess historical ratings of ag-gression, also found history of aggression with theexception of suicide attempt, clearly distinguishedbetween aggressive patients and control subjects.The authors suggested that suicidal behaviour,being generally less common, may not be a hall-mark of the aggressive patient.

The aggressive group had significantly higherpremorbid history of aggression scores than thenon-aggressive group, supporting the importanceof trait factors in determining aggression. How-ever, repeated measures ANOVA showed that,for the aggressive group, the subjects becamesignificantly more aggressive after the onset ofschizophrenia, suggesting the joint effects of traitfactors and schizophrenia symptomatology in de-termining aggression.

We unexpectedly failed to find any significantdifferences between the aggressive and non-ag-gressive groups in relation to neuroleptic motorside effects and thus did not consider them incomparing the importance of state vs. trait fac-tors. The probable reasons for the lack of signifi-

Žcant results are discussed elsewhere Cheung et.al., 1997c .

The effects of HDHQ and MMPI PD scores aswell as MOAS scores on aggressive grouping re-mained significant after controlling for the overalllevel of schizophrenia symptomatology, suggestingthat their effects were independent of the latter.The effect sizes of the former were similar to thelatter, suggesting that they would be of similarimportance in determining aggression. Eventhough the effect of HDHQ, MMPI PD andMOAS scores remained significant after con-trolling for negative affect in response to halluci-nationsrdelusions, the effect sizes of the formerwere much smaller than the latter, suggesting thatnegative affect would be much more important indetermining aggression than the dispositionalvariables.

In summary, we have found independent ef-fects of hostility and antisocial traits in determin-ing aggressive behaviour in schizophrenia patientsin rehabilitation wards. This is supported by ourdata on historical ratings of aggression. Our find-ings thus support the conventional clinical wis-dom of taking into account personality traits andpast history of aggression in determining the like-lihood of aggressive behaviour in schizophrenia.However, their effects were modest and similar tothe total PANSS score, but were much smaller incomparison to those of negative affects associatedwith hallucinations and delusions. Our patientsample comprised mainly long-stay psychiatric


patients with a relatively long duration of illness.The study needs to be replicated in other settingssuch as acute wards and the community to de-termine how applicable our findings would be toschizophrenia in general. Our study has only ex-amined several key correlates of aggression inschizophrenia as we intended to study them indepth. However, there is also a need to examine alarge number of risk factors in the same study tocompare predictive significances and examine in-

Ž .teractions Steadman et al., 1993 .

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Aggressive behaviour in schizophrenia: role of state versus trait factors

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