by Michael McKeon, Lecturer in Nursing, Dublin City University


There is a strong association both real and mystical, between intellectual disability and people who have offended in law. Only a minority of offenders have a formal intellectual disability, but certain sexual offences, especially indecent exposure and arson, are over-represented in the population of people with intellectual disabilities. For people with intellectual disabilities who do offend in law, a full range of therapeutic options should be available from psychosocial to pharmacological interventions. Psychosocial interventions should take account of the developmental levels of the offender and pharmacological interventions need to be approached more cautiously in people with neurodevelopmental disorders. Much more research is needed to establish evidence-based practice in this area WHICH AREA—OFFENDING OR PHARMACOLOGICAL INTERV? as current practice is informed by knowledge from studies in the general population without intellectual disability (Gates 2003).

It is not a new suggestion that people with intellectual disabilities are viewed as deviants and lawbreakers. Wolfensberger (1972) identified eight social role perceptions of people with intellectual disabilities, one of which described such people as ‘a menace’. This notion of menace has developed over a long period of time and has allowed people with intellectual disability to be easily associated with offences, juvenile courts, police and the prisons systems. From a historical context, the idea of ‘Social Darwinsim’ developed at the turn of the 1900s, with the idea that the human race depended on a healthy pool of genes, which could be contaminated by intellectual disability and other forms of deviant or criminal behaviour. At that time politically motivated projects by researchers in America on two specific families, the Jukes family and the Kallikak family, attempted to prove a three-point argument that criminal behaviour was inherited, that intellectual disability was inherited, and that criminal behaviour was linked to intellectual disability. These projects and the subsequent beliefs of Social Darwinsim led to the segregation of many men and women with intellectual disabilities in isolated institutions and entrenched many negative ideas of intellectual disability—one of which was the positive association with criminal behaviour (Gates 1997).

Studies carried out in Europe, Australia and America have all put forward the view that people with intellectual disability are over-represented in the prison population (Hayes 1997). While many of the studies appear straightforward, others have used methods that may not provide a true representation, owing to the complex nature of assessment for those with an intellectual disability and the complexity of the prison system. Thus some caution should be exercised interpreting these studies.

In America it is reported that, on average, 9.5% of reported IQ scores in prison populations are below 70, which is the cut-off level typically used to indicate an intellectual disability. In some states the proportion of prisoners with intellectual disability was as high as 24% (Brown and Courtless 1971). A Danish study found a prevalence rate of 10% in the general prison population—based on information collected in the 1920s. More recent studies indicate that the majority of prisoners with intellectual disabilities in Denmark are diverted to specialised services prior to sentencing (Svendsin and Werner 1997). In Australia, surveys found that 2% of the prison population had IQs below 70- However, when adaptive behaviour was included in the assessment, up to 12% of the prisoners were identified as having of an intellectual disability (Hayes and McIlwain 1988). Studies in Britain suggest that fewer than 2% of prisoners have an intellectual disability, and that the majority of offenders with intellectual disabilities are located in secure hospitals rather than prisons (Murphy et al. 2000).

In 1999, the Irish Department of Justice, Equality and Law Reform commissioned a survey on the level of intellectual disability in Irish prisons. Psychological assessments were conducted on 264 prisoners selected randomly within the fourteen Irish prisons; this represented 10% of the total prison population. The overall findings of the survey showed that 28.8% of the sample population scored below 70 on intelligence tests, which suggests a significant degree of intellectual disability within the people in the Irish prison system (Murphy et al. 2000).

A survey of the level of learning disability among the prison population In Ireland (Murphy et al. 2000) sought to provide a picture of intellectual disability within the Irish prison system. Having acknowledged the difficulties experienced in similar studies in other countries, the Irish study is the first comprehensive survey to estimate the prevalence of intellectual disabilities in the Irish prison population with established validity and reliability. One of the strong aspects of this study was the application of rigorous procedures: assessments were administered and scored by qualified clinical or educational psychologists with extensive experience in psychometric testing and intellectual disabilities. One of the limitations to the study was the fact that only nine women were tested, too few to allow for accurate recommendations for women prisoners.

Survey findings

  • 8% of prisoners scored below an IQ level of 70,
  • 3% had a deficit in reading,
  • 6% had a deficit in spelling,
  • 5% had a deficit in maths.

Employment information found from the assessments:

  • 6% had no job prior to coming to prison,
  • 3% described themselves as unskilled,
  • 7 % reported working at a management level,
  • 3% worked at a professional level.

Level of school attendance was:

  • The average school-leaving age of prisoners was 14.6 years,
  • 80% had never been seen by a school counsellor or psychologist,
  • 5% had been suspended from school,
  • 2% had been expelled from school,
  • 4 % had never sat formal secondary school examinations,
  • 6% had sat the Leaving Certificate examinations.

The study endeavoured to provide an explanation for such a high level of people with intellectual disability in the prison system. ‘The most telling reason why this is the case is the fact that the only agencies that cannot engage in a “gate-keeping” exercise are the corrective services and the juvenile justice system; they must receive all people who have been remanded or sentenced.’ Organisations that provide support for people with intellectual disability often lack the necessary resources to meet the complex needs of individuals who exhibit challenging behaviour—increasing the likelihood that they may become offenders and end up in the courts (Murphy et al. 2000).

Another important factor evidenced in the study is the negative school experience of so many children/young people with special needs in Ireland—the absence or inability to access appropriate educational services and the difficulty in actually staying within the school system pointed towards the increased likelihood that people with intellectual disability would end up in the prison system (Murphy et al.2000).

With no special services to identify people with intellectual disability who come into contact with the criminal justice system, the Gardaí and the legal profession are the only caretakers who can prevent people with intellectual disability being discarded into the prison system. However, in a number of studies (Bean and Nemitz 1995, Palmer and Hart 1996) both the police and the defence lawyers were found to have little knowledge of intellectual disability. With no real experiential understanding, they relied on behaviours and personal factors as a way of determining the presence of intellectual disability. The way forward here is to provide a psychologist to assess a person suspected of having an intellectual disability, before allowing a person into the court or prison system.

Most individuals in the prison system have predictable histories of delinquency. Most of the people with intellectual disability in Irish prisons have been exposed to the same risk factors as their non-disabled peers—childhoods characterised by chronic financial disadvantage and instability. ‘The nature of their disability presents additional challenges to services for the prevention and management of criminal behaviour.’

The authors strongly recommend (as did the UK study by Clare and Murphy (1999)), the establishment of specialised support services which take into account the unique needs of people with intellectual disability within the criminal justice and education systems. They also recommended five specific areas for improving and developing appropriate services:

  1. early identification and support
  2. development of diversion services
  3. specialised prison programmes
  4. post-release services
  5. priorities for immediate action:
    • ‘Screening system for all offenders when they first contact the criminal justice system to identify those who potentially have intellectual disability.
    • Comprehensive psychological assessment for all offenders identified as potentially having intellectual disability.
    • Training for Gardaí, Probation Officers and Wardens regarding the needs and appropriate supports for people with intellectual disability.
    • Development of educational programmes in prisons, specifically designed to address the needs and learning characteristics of individuals with intellectual disability.’ (Murphy et al. 2000).

With recommendations of this report left gathering dust as many reports do, the priorities for immediate action need to be implemented with urgency, in order to deal with the high number of individuals with an intellectual disabilities in the prison population.


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