The Scientific Evidence

Some mental health campaigners have claimed that the association between violence with mental illness is ‘modest’, or non-existent.

Some even claim it is a ‘myth’.

Consistent evidence from many international scientific studies shows this view is incorrect. The association between mental illness and violence is actually of the same order as that between smoking and cancer.


1. In 1981, Petursson and Gudjonsson studied all homicide offenders In Iceland between 1900 – 1979 and found a third were psychotic or mentally disordered.[1]

2. A study by Taylor & Gunn in 1984 in Greater London prisons found offenders had a high rate of psychiatric disorder. Those convicted of homicide had a substantially higher prevalence of schizophrenia than would be expected from the general population.[2]

3. In 1986 in Northern Sweden an investigation by Lindqvist found more than half the people convicted of a homicide between 1970 and 1981 had a major mental disorder.[3]

4. In Copenhagen in 1987 an in-depth study by Gottlieb, Gabrielsen and Kramp of all those convicted of homicide over a 25 year period found 23% of homicide offenders were psychotic at the time of the offence.[4]

5. In the United States in 1990 Swanson investigated a community based sample of 10,000 and asked people if they had committed any violent action over the last 12 months. Violence was reported by 2% of those with no psychiatric diagnosis, by 8% of those with pure schizophrenia, and by 13% of those whose schizophrenia was complicated by substance misuse or personality disorder.[5]

6. The same year in Sweden, Lindqvist and Allebeck followed 644 schizophrenic patients over 14 years and confirmed the violent crime rate for schizophrenics was four times higher than for non-patients. They also showed how risk was increased by drugs and alcohol.[6]

7. Two years later in another large Swedish study, Hodgins, found men with major mental health disorders were four times more likely to be registered for violent offences than those with no such disorder.[7]

8. In New York in 1992, Link, Andrews & Cullen compared arrests and reported violence for two different groups – one of patients with a mental health problem , the other never having had MH treatment. They found the psychotic patient group had higher rates on all measures of violent/illegal behavior,[8]

9. Also in 1992 this time in Canada, a study by Cote and Hodgins found some 35% of homicide offenders met lifetime criteria for a major mental disorder.[9]

10. In the United States in 1993 Lidz, Mulvey & Gardner – followed up 357 patients in a psychiatric emergency room for six months – and found 45% of all cases went on to commit violent acts.[10]

11. Finnish studies by Erohnen, Tiihonen and Hakola 1996 (a and b) of 693 homicide offenders over eight years found significant increased risk of homicidal violence by people with schizophrenia – 10 times greater risk than for the general population.[11]

12. Danish studies of 400,000 people born between 1944 and 1947 showed a distinct association between schizophrenia and violence. People with psychosis orschizophrenia were significantly more likely to be arrested for criminal violence than people who had never been hospitalized (Hodgins et al 1996, Brennan et al 2000).[12] 

13. In 1997 in Israel, a study by Stueve & Link found psychotic disorder
increased the risk of fighting and use of weapons.[13]

The risk of criminal behaviour was significantly higher among people with psychotic disorders

14. The same year a large scale study examining 12,000 people in North Finland over 26 years, Tiihonen et al 1997, found the risk of criminal behaviour was significantly higher among people with psychotic disorders, In particular they found those with alcohol-induced psychoses and schizophrenics with coexisting substances abuse had a higher risk for violent behaviour.[14]

15. In 1998 a European study, Eronen, Angemeyer & Schulze 1998, reported people with schizophrenia and other psychotic disorders were significantly more likely to commit violent acts than other members of the population.[15]

Schizophrenia was most strongly associated with personal violence

16. The same year, a British study, Taylor et al 1998, examined the association between mental disorder and violence in a survey of 1740 patients resident in a high security hospital. They found Schizophrenia was most strongly associated with personal violence. The found more than 75% of those with a psychosis were driven to offend by their delusions.[16]

17. Also in 1998 Belfrage followed up more than a thousand schizophrenic or psychotic patients in Stockholm ten years after their discharge from hospital, and found more than 40% had received a criminal convictions, mostly for violent crimes. The rate for the general population was less than 10%. [17]

18. In 1999, a British study by Shaw et al, found substantial rates of mental disorder in people convicted of homicide. They found 14% of perpetrators had symptoms of mental illness at the time of the offence.[18]

19. In 2000, the MacArthur Violence Risk Assessment study in the United States, of 951 recently released psychiatric patients found more than quarter (27%) committed an act of serious violence (battery resulting in physical injury, sexual assault, assault involving the use of a weapon, or threat made with weapon in hand) within a year of their release.[19]

20. In New Zealand in 2000, Arsenault et al studied 961 young adults in Dunedin between 1972-73, and found In the age group committing most violent incidents, people with mental disorders accounted for a considerable amount of violence in the community. They found 10% of violence risk was uniquely attributable to people with schizophrenia or similar disorders.[20]

21. In Britain, a study by Sanders et al examined 114 patients admitted to a general psychiatric ward in Middlesbrough found that almost a quarter of patients reported thoughts of violence directed at specific individuals. Nearly 1 in 10 admitted to owning weapons and one in 20 to carrying them.[21]

22. The following year a landmark investigation in Britain by Walsh et al, of 700 psychotic patients found that 22% participants physically assaulted another person within the two years of the study.[22]

It is now accepted that people with schizophrenia are significantly more likely to be violent than other members of the general population

23. A study by the same researchers in 2002 in the British Journal of Psychiatry noted “It is now accepted that people with schizophrenia are significantly more likely to be violent than other members of the general population.”[23]

24. That same year a landmark study of more than 15,000 people in Stockholm, Hodgins & Janson, found a distinct association between mental illness and crimes of violence. They found in countries with relatively low crime rates, the crimes committed by the mentally ill, particularly violent crimes, represent a significant proportion of all crimes.[24]

25. In 2004 in Austria a major 25 year study of 1087 homicide perpetrators by Schanda et al. found Major Mental Disorders were associated with an increased likelihood of homicide (two-fold in men and six-fold in women). They confirmed the risk was increased if the patients also abused drugs and or alcohol.[25]

26. Also in 2004 a major Swedish study by Fazel & Grann of more than 2000 people convicted of homicide or attempted homicide between 1988 and 2001, found 90% of people convicted for homicide had a psychiatric diagnosis, with nearly 20% having a psychotic illness.[26]

27. The same year a study by Soyka et al, in Germany found significant levels of violence (particularly physical assault) in 1700 schizophrenic patients following their release from hospital.[27]

28. Also that year a landmark study by Wallace, Mullen & Burgess in Victoria, Australia following 2861 patients with schizophrenia over a 25 year period found a significant association between schizophrenia and a higher rate of criminal convictions, particularly for violent offences.[28]

9. In 2006 a nationwide study of 1410 schizophrenic patients across the United States by Swanson et al found 19% were involved with some form of violent behaviour with nearly 4% committing acts serious violence over a six month period. Serious violence was associated with psychotic and depressive symptoms, childhood conduct problems, and victimization.[29]

People with schizophrenia make a significant contribution to violence in our communities. There is a substantial and clinically relevant association between schizophrenia and violence.

30. Also in 2006, another major study by Paul Mullen in Australia wrote that “People with schizophrenia make a significant contribution to violence in our communities” He said there is “a substantial and clinically relevant association” between schizophrenia and violence and that “the 10% or so from which will emerge the perpetrators of most of the serious violence are identifiable in advance”.[30]

“In scientific terms the existence of a link between mental disorder and violence is no longer controversial, [it is] of a similar order of magnitude to the association between smoking and lung cancer.”

31. In 2007 in his book ‘Treating Violence’ Professor Tony Maden, Professor of Forensic Psychiatry at Imperial College and Consultant Psychiatrist at Broadmoor High security hospital wrote – “In scientific terms the existence of a link between mental disorder and violence is no longer controversial… There is a highly significant association between psychotic mental illness and violence in the community, of a similar order of magnitude to the association between smoking and lung cancer.”[31]

This association between schizophrenia and violent offending is robust

32. Finally in 2008, Sheilagh Hodgins summed up the level of research on schizophrenia and violence when she wrote

“This association between schizophrenia and violent offending is robust: it has been observed by different research teams who recruited samples from countries with different cultures and health and justice systems, and who measured the association of schizophrenia and offending using different experimental designs including longitudinal investigations of birth and population cohorts, comparisons of people with schizophrenia and their neighbours, and diagnostic studies of random samples of convicted offenders.”[32]


Previous claims

Prof Pamela Taylor calls the association between mental illness and violence “modest” NHS National Programme on Forensic Mental Health Research. Mental Illness and Serious Harm to others. (nd) Page 8

“Myth” quote is from Time to Change campaign


1. H. Petursson & G.H. Gudjonsson, Psychiatric aspects of homicide. Acta Psychiatrica Scandinavica, 64, (1981) 363-372.


2. P J Taylor, J Gunn. Violence and psychosis. I. Risk of violence among psychotic men. British Medical Journal (Clin Res Ed) 1984;288:1945-1949


3. P Lindqvist. Criminal Homicide in North Sweden. : Alcohol intoxication, alcohol abuse and mental disease. International Journal of Law and Psychiatry, 8, (1986) 19 -37


4. P. Gottlieb, G. Gabrielsen, & P. Kramp. Psychotic homicides in Copenhagen from 1959 to 1983. Acta Psychiatrica Scandinavica, 76, (1987) 285-292.


5. JW Swanson, CF Holzer, VK Gangu, RT Jano. Violence and psychiatric disorder in the community: evidence from the epidemiological catchment area surveys. Hosp Community Psychiatry 41:761-770, July 1990


6. P Lindqvist and P Allebeck: Schizophrenia and crime. A longitudinal follow-up of 644 schizophrenics in Stockholm. British Journal of Psychiatry 157: 345-350 (1990)


7.S Hodgins. Mental disorder, intellectual deficiency and crime. Evidence From a Birth Cohort. Arch Gen Psychiatry 1992; 49: 476-483


8. B Link, H Andrews, F Cullen. The Violent and Illegal Behavior of Mental Patients Reconsidered, American Sociological Review. Vol 57(3), Jun 1992, 275-292.

9. G Cote and S Hodgins. The prevalence of major mental disorders among homicide offenders. International Journal of Law and Psychiatry, 15,(1992) 89 – 99

10. C Lidz, E Mulvey, W Gardner, The Accuracy of Predictions of Violence to Others Journal of the American Medical Association. 1993 ; 269 (8) : 1007-1011.

11. a. M Eronen.; P Hakola ; J Tiihonen; Mental disorders and homicidal behavior in Finland Arch Gen Psychiatry 1996, vol. 53, no6, pp. 497-504
b. Markku Eronen, Jari Tiihonen and Panu Hakola Schizophrenia and Homicidal Behavior Schizophrenia Bulletin 1996 22(1):83-89;

12. a. S Hodgins; S Mednick; P Brennan; F Schulsinger; M Engberg. Mental Disorder and Crime. Evidence From a Danish Birth Cohort. Arch Gen Psychiatry. 1996; 53(6):489- 496.
b. P Brennan; S Mednick; S Hodgins. Major Mental Disorders and Criminal Violence in a Danish Birth Cohort : Arch Gen Psychiatry. 2000; 57:494-500.

13. A Stueve and B Link, Violence and Psychiatric Disorders: Results from an Epidemiological Study of Young Adults in Israel. Psychiatric Quarterly, Vol 68, No 4 / Dec 1997 327-342

14. J Tiihonen, M Isohanni, P Rasanen, M Koiranen, J Moring. Specific major mental disorders and criminality: a 26 year prospective study of the 1996 Northern Finland birth cohort. Am J Psychiatry 1997; 154: 840-845

15. M. Eronen, M.C. Angermeyer, B. Schulze. The psychiatric epidemiology of violent behaviour. Soc Psychiatry Psychiatr Epidemiol (1998) 33: p 13 – 23

16. PJ Taylor, M Leese, D Williams, M Butwell, R Daly and E Larkin, Mental disorder and violence. A special (high security) hospital study. British Journal of Psychiatry 172: 218-226 (1998)

17. H Belfrage. A Ten Year Follow-Up of criminality in Stockholm mental patients. New Evidence for a Relation between Mental Disorder and Crime. British Journal of Criminology 38:145-155 (1998)

18. J Shaw, L Appleby, T Amos, R McDonnell, C Harris, K McCann, K Kiernan, S Davies, H Bickley, R Parsons, Mental disorder and clinical care in people convicted of homicide: national clinical survey. BMJ 1999;318:1240-1244

19. HJ Steadman, E Silver – Immediate Precursors of Violence among persons with Mental Illness – A return to a Situational Perpective. In : Sheilagh Hodgins (Ed) Violence among the mentally ill: Effective Treatments and Management Strategies. Dordrecht (Netherlands) 2000 Pages 35– 48,

20. L Arseneault, TE Moffitt , A Caspi , PJ Taylor , PA Silva . Mental disorders and violence in a total birth cohort: results from the Dunedin Study. Arch Gen Psychiatry. 2000 Oct;57(10): 979-86.

21. J Sanders, S Milne, P Brown, AJ Bell, Assessment of aggression in psychiatric admissions: semi-structured interview and case note survey. BMJ 2000; 320:1112

22. E. Walsh C Gilvarry, C. Samele, K.Harvey, C.Manley, P Tyrer, F. Creed, R. Murray, and T Fahy Reducing violence in severe mental illness: randomised controlled trial of intensive case management compared with standard care. BMJ. 2001; 323(7321): 1093.

23. E Walsh; A Buchanan; T Fahy; Violence and schizophrenia: examining the evidence : British Journal of Psychiatry (2002) 180: 490-495

24. S Hodgins and C Janson: Criminality and Violence among the Mentally Disordered: The Stockholm Project Metropolitan : Cambridge University Press, 2002

25. Schanda et al. Homicide and major mental disorders: a 25-year study. Acta Psychiatr Scand 2004: 110: 98–107

26. S Fazel, and M Grann. Psychiatric Morbidity Among Homicide Offenders: A Swedish Population Study Am J Psychiatry 161:2129-2131, November 2004

27. M Soyka, V Morhart-Klute , H Schoech . Delinquency and criminal offenses in former schizophrenic inpatients 7-12 years following discharge. Eur Arch Psychiatry Clin Neurosci. 2004 Oct; 254(5) : 289-94.

28. C Wallace, P E. Mullen, P Burgess. Criminal Offending in Schizophrenia Over a 25-Year Period Marked by Deinstitutionalization and Increasing Prevalence of Comorbid Substance Use Disorders. Am J Psychiatry 161:716-727, April 2004

29. JW. Swanson; M Swartz; R Van Dorn; E Elbogen; H. R Wagner,; R Rosenheck; T. Stroup; J McEvoy; J Lieberman: A National Study of Violent Behavior in Persons With Schizophrenia. Arch Gen Psychiatry. 2006;63:490-499.

30. P Mullen. Schizophrenia and violence: from correlations to preventive strategies Advances in Psychiatric Treatment (2006) 12: 239-248

31. A Maden, Treating Violence (Oxford 2007) – p 23

32. S Hodgins. Violent behaviour among people with schizophrenia: a framework for investigations of causes, and effective treatment, and prevention. Phil. Trans. R. Soc. B 12 August 2008 vol. 363 no. 1503 2505-2518

2 Replies to “The Scientific Evidence”

  1. This is fantastic; you wouldn’t happen to know if there’s anything like this in the United States, would you? Great information. This level of transparency is just so refreshing and encouraging. Thanks!

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