A research on mentally-disabled prisoners in Japanese prisons


Yokohama National University, Faculty of Education and Human Sciences,
Department of Disability Studies           


The Annual Report of Statistics on Correction published by Japanese Ministry of Justice contains a section with the title, “Intelligence Quotient of Newly Convicted Prisoners”. According to the annual report from 2006, 7,097 of the 30,277 newly convicted prisoners (approximately 23%) scored 69 points or lower on the IQ test. Including 1,926 new inmates who were categorized as “untestable”, nearly 30% of all newly convicted prisoners are considered mentally-challenged1).

This paper will first investigate the accuracy of the above data. If this initial investigation provides that there are a significant number of mentally-challenged inmates in Japanese prisons, we will then attempt to find out what systematical problems have contributed to creating such a condition in concern with the provision of educational and welfare programs to the mentally challenged prisoners. Finally, we will attempt to seek possible measures our government can employ in the future in addition to what has already been introduced or planned for the future introduction.

2. Percentage of the mentally disabled individuals in Japanese prisons

The accuracy of the data provided by the Annual Report of Statistics on Correction has been questioned because it is entirely based on CAPAS, an mass intelligence assessment test solely developed by the Japanese prison system. In order to reevaluate the accurate condition, an research was held in 2006 against 27,024 inmates from 15 randomly selected prisons. The result of this research, which was mainly based on the individual intelligence assessment test scores as well as examination provided by professional psychiatrists, indicated that the number of those who were diagnosed as mentally disabled was indeed much fewer: only 410 individuals, or 1.5% of all newly sentenced inmates2). Aside from this unexpected result, the research revealed yet another even more critical problem; Among the 410 individuals who were diagnosed with mental disability, only 26 (or 6.3%) had been provided with the Certificate of Mental Retardation. The Annual Report of Statistics on Correction from 2006 indicates that 7,563 individuals out of 33,032 newly convicted prisoners had IQ scores of 69 or less on CAPAS, yet only 265 of them possessed the certificate4). If it is true that only 6.3% of mentally disabled inmates under the current condition possess the Certificate of Mental Retardation as the 2006 research has suggested, 4,206 (or 12.7%) newly-convicted prisoners are estimated to be mentally disabled and therefore had the right to possess the certificate. 

  We estimate the number of mentally disabled inmates in Japanese prisons to be somewhere between 10 to 15% of all inmates. This estimate corresponds with the data reported by Norwegian researchers that showed 10.8% of all prisoners in Norway is mentally-disabled5).

3. The mental disability and social welfare

  According to the 2005 Annual Report on Government Measures for Persons with Disabilities published by Japan Cabinet Office, of the total estimated number of 3,600,000 persons with mental disability, 459,000 persons possess the Certificate of Mental Retardation. In other words, roughly 12% of all mentally disabled people in Japan possess the certificate. In contrast, the percentage of mentally disabled inmates who possess the certificate is limited to as low as 6.3%, revealing that for whatever reasons, the percentage of certified individuals in the prisons is approximately half of what it is in the external environment. This clearly indicates a tendency that people who are bound to be in prisons are less likely to have possessed Certificate of Mental Retardation, and therefore less likely to have received some form of assistance from social welfare programs.

4. From prisons to welfare and education

  According to the Annual Report of Statistics on Correction, more than 70% of all mentally disabled prisoners have a history of at least one prior imprisonment, while roughly 20% of them are repeat offenders with more than ten prior convictions. This negative cycle has created a condition under which the prisons are substituted as institutions for mentally disabled in some ways. Most of the mentally disabled prisoners are sentenced after committing less serious crimes. After leaving the prisons, many of them are, without a chance to receive social welfare, bounded to live as homeless or under similar conditions, ultimately ending up committing another crime such as theft or skipping on a check and returning to the prisons. This habitual behavior is presumably triggered, at least in part, by the fact that many of the mentally disabled prisoners do not possess the Certificate of Mental Retardation, staying beyond the reach of social welfare. With the lack of the advantage of possessing the Certificate of Mental Retardation, such as tax exemption and receiving the employment mediation services, a mentally disabled person with a criminal history is much more likely to be forced into committing secondary crime after having difficulty in sustaining a minimum lifestyle. Furthermore, social welfare facilities tend to be hesitant to offer services to those persons with criminal history without the disability certificates.

On May 18th of 2008, The Ministry of Justice (MOJ) introduced a new law in regards to the treatment of prisoners, and mandated prisoners to attend rehabilitation programs depending on the types of crimes committed. Furthermore, the research center of the Ministry of Health, Labor, and Welfare (MHLW) has suggested both MHLW and MOJ to 1) establish a publically operated reform center in each prefecture to connect prisons to various welfare organizations, and to 2) relax the qualification requirements for the Certificate of Mental Retardation.

In addition, a collaboration between MHLW and MOJ has developed a plan to establish a rehabilitation center by the end of 2009, in which the ex-prisoners can seek  a career as a farmer5).

Lastly, it should be mentioned that the welfare standard employed by the city of Yokohama sets the cut-off IQ score at 75 points measured by Tanaka-Binet Scale of Intelligence. This means that 5.9% of all population on average is categorized as intellectually disabled. However, the percentage of children who are classified as mentally disabled and have been receiving special education as well as social welfare is stagnant at 1%. Because the Certificate of Mental Retardation is only issued upon request, many of the parents/guardians are reluctant to apply due to the fear of being stigmatized. This is especially true for a mild case of mental retardation. Lack of appropriate education and opportunity to receive social welfare can lead the children with mental disability to anti-social behavior, ultimately connecting them to crimes. Therefore, guardians should be strongly recommended to apply for the certificate without hesitation while the public organizations in education and social welfare must be aware of the social conditions that surround the mentally disabled children and attempt to provide the best service possible to improve the future of the children with mental disabilities. 


1) Annual Report of Statistics on Correction: the Ministry of Justice, 2006
2) Mainichi Shinbun, June 20, 2007.
3) Press release by the Ministry of Justice, October, 2006.
4) The prevalence and nature of intellectual disability in Norwegian prisons S.Snderna., K.Rasmussen, T.Palmstierna & J.Nøttestad: Journal of Intellectual Disability Research, Vol.52.p1129-1137.2008.
5) Press release by the Ministry of Welfare and Labor and the Ministry of Justice, 2008: Mainichi Shinbun, July 11, 2008.
6) Akiko Yoshida, Tomoko Sugano, Takeshi Matsuishi: Mental Retardation Incidence in Yokohama City. Journal of disability and medico-pedagogy.Vol.5.p16-17.2002.(originally published on Journal of disability and medico-pedagogy, Vol.20.2009.p.1-3)