Fact Sheet: Mentally Ill Offenders

About the fact-sheet series: Fact sheets summarize current literature into a short (2 page) document intended for distribution. Fact-sheets are extremely useful for academics, professionals or laypeople who are in contact with offenders, victims, corrections or the legal system in any way. They provide a means to disseminate empirically based information in a way that is both quick and useful.
About the authors: This article was co-authored. The primary author was Danielle Andrewartha, EAPL-S representative for Australia and Ph.D. student at Monash University. The co-author and editor was Julia Shaw, EAPL-S co-president and Ph.D. student at the University of British Columbia (Canada).

View this document in it's full glory by downloading the pdf here.

Remember to also read our fact sheet on the insanity defense!

Mentally ill offenders

There is a high prevalence of misconceptions regarding mentally ill individuals and the risk they pose to the public. Common questions on this topic include: Are mentally ill individuals more likely to be violent? How do police deal with mentally ill individuals? What is the insanity plea?

This fact-sheet is intended to aid those who are interested in the link between mental illness and offending by reviewing information on prevalence rates of mental illness, law enforcement strategies, how courts deal with mental illness, and the insanity defense.

Prevalence and perceptions

Approximately one in four people will experience some form of mental illness during their lifetime.[1]  Up to 75% of the population consider people with mental illnesses to be dangerous2 and believe “that the public should be better protected from [them]”.3  While there is some data that supports this concern,4 it has been criticized as unreliable on a number of grounds.5 Although there is an elevated risk of violence posed by mentally ill individuals, especially those who experience so-called TCO symptoms (thought-control-override), this risk needs to be considered in context. Characteristics such as being young, male, and engaging in hazardous drinking are all significantly better predictors of violence than mental illness.6

Mental illness and criminal justice

Despite increasing awareness about the nature and causes of mental illness, the stigmatization of severe mental disorders may be intensifying in response to the powerful perceived correlation between mental disorder and dangerousness.7  As a result of the stigma attached to mental illness, which may prevent affected persons from seeking treatment, and the deficit in mental health care resources; people with mental illnesses are at increased risk of becoming entangled in the criminal justice system.8

Around 7% of all people with whom police officers have contact have a mental illness.9  Police officers have broad discretionary powers when they encounter someone whom they suspect is suffering from a mental disorder.  They may: arrest him or her, take the individual for psychiatric assessment or refer him or her to appropriate mental health services.  Police officers may, like the majority of the general population, believe there is a robust correlation between mental illness and risk of violence. Although it is uncertain whether individuals with mental illnesses are more likely to be arrested than those without, this misconception arguably affects the ways in which police officers treat members of the public who present signs of mental illness.

Court context

As with law enforcement officials, judges and jurors might also adopt stereotypical misconceptions, such as the view that people with mental disorders are responsible for their conditions and can control their behavior if they try, and believe that shocking crimes committed by people with mental illnesses are representative of all people with mental illness. It may be as a result of these attitudes that offenders with mental disorders have higher rates of conviction and often receive harsher sentences. The rates of mental illness among incarcerated persons are approximately 16% of all males and 24% of all females.  These rates are four to five times higher than the levels of mental illness within the general population.10

Insanity defense

When a defendant claims to not be criminally responsible on account of mental disorder, they are using the insanity defense. While it is often referred to by other names, many countries have some version of the insanity defense. This defense is designed for people who do not have the capacity for understanding right and wrong at the time of their criminal act, and to help them get treatment.11 For a mentally ill individual to be considered not responsible for a criminal act there has to be strong evidence to suggest that their particular mental illness (or symptoms thereof) directly caused the criminal behavior, and that they did not understand the consequences of their actions at the time of the offence. Simply having a mental illness is not enough to justify this defense. For example, a mother who is schizophrenic and experiences hallucinations that command her to kill her children because they are actually spawns of the devil would likely be eligible for the insanity defense. However, her schizophrenia alone would not suffice as a legal excuse for her actions. Because this kind of defense is often hard to uphold, it is used only in rare cases and is often not successful in court.


Overall, the current literature suggests that although mental illness is overrepresented in prisons and jails, mental illness is not typically a risk factor for dangerousness. Unfortunately the criminal justice system often overlooks this and is overall more likely to sentence the mentally ill. Finally, the insanity defense provides an avenue for those whose mental illness has caused criminal behavior to get the help they need.

Quick summary

  • Mental illness is not typically a risk factor for dangerousness
  • Only few symptoms of mental illness may contribute to violence (particularly TCO symptoms)
  • Misconceptions contribute to higher rates of mental illness in the criminal justice system
  • The insanity plea helps those whose mental illness has caused criminal behavior to get the help they need

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1.     Ronald Kessler et al, ‘Prevalence, Severity, and Comorbidity of Twelve-month DSM-IV Disorders in the National Comorbidity Survey Replication (NCS-R)’ (2005) 62(6) Archives of General Psychiatry 617.

2.     Bruce Link et al, ‘Public Conceptions of Mental Illness: Labels, Causes, Dangerousness, and Social Distance’ (1999) 89 American Journal of Public Health 1328.

3.     Simon Braunholtz et al, Well? What Do You Think? (2006): The Third National Scottish Survey of Public Attitudes to Mental Health, Mental Well-being and Mental Health Problems (2007) [31] <http://www.scotland.gov.uk/Resource/Doc/197512/0052833.pdf> at 20 June 2011.

4.     See, for example, Judith Rabkin, ‘Criminal Behavior of Discharged Mental Patients: Critical Appraisal of the Research’ (1979) 86 Psychological Bulletin 1.

5.     See for critique and analysis Patrick Corrigan and Amy Cooper, ‘Mental Illness and Dangerousness: Fact or Misperception, and Implications for Stigma’ in Patrick Corrigan (ed), On the Stigma of Mental Illness: Practical Strategies for Research and Social Change (2005) 165, 167-70.

6.     See, for example, Patrick Corrigan and Amy Cooper, ‘Mental Illness and Dangerousness: Fact or Misperception, and Implications for Stigma’ in Patrick Corrigan (ed), On the Stigma of Mental Illness: Practical Strategies for Research and Social Change (2005) 165; Jeremy Coid et al, ‘Violence and Psychiatric Morbidity in the National Household Population of Britain: Public Health Implications’ (2006) 189(1) The British Journal of Psychiatry 12.  See generally: EAPL-S Fact Sheet – Risk Assessment at www.eaplstudent.com.

7.     A Stier S and Hinshaw, 'Explicit and Implicit Stigma against Individuals with Mental Illness' (2007) 42(2) Australian Psychologist 106.

8.     See for discussion D Andrewartha “Words Will Never Hurt?: Media Stigmatisation of Mental Illness in the Criminal Justice Context” (2010) 35(1) Alternative Law Journal 4.

9.     D Chappell, ‘Policing and Emotionally Disturbed People: Disseminating Knowledge, Removing Stigma and Enhancing Performance’ (2008) 40 Australian Journal of Forensic Sciences 37, 38. 10

10.  Stephanie Hartwell, ‘Triple Stigma: People With Mental Illness and Substance Abuse Problems in the Criminal Justice System’ (2004) 15 Criminal Justice Policy Review 84, 87.

11.  Torry, Z. D., & Billick, S. B. (2010). Overlapping universe: Understanding legal insanity and psychosis. Psychiatric Quarterly, 81(3), 253-262. doi:10.1007/s11126-010-9134-2

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Overview of Fact Sheet topics covered to date