Mental Retardation

mental retardation, below average level of intellectual functioning, usually defined by an IQ of below 70 to 75, combined with limitations in the skills necessary for daily living. Daily living skills include such things as communication, the ability to care for oneself, and the ability to work. The definition of mental retardation has evolved over the years. Prior categorizations of mental retardation, defined solely by IQ, have largely been abandoned in favor of an approach that looks at how much support the retarded person needs in various areas of his or her life at any given time. Such support can range from intermittent help in such things as finding housing or a job, to pervasive, daily, lifelong help in all areas.


There are several hundred possible causes of mental retardation. They include genetic conditions (e.g., Down syndrome, fragile X syndrome); prenatal problems (e.g., fetal alcohol syndrome, rubella, malnutrition); problems apparent at birth (e.g., low birth weight and prematurity); and problems that occur after birth (e.g., injuries and childhood diseases like measles that can lead to meningitis and encephalitis). The most commonly identified causes of mental retardation are Down syndrome, fragile X syndrome, and fetal alcohol syndrome. In many cases the cause is never known.


Most mentally retarded children are capable of learning new things, both in and out of a formal school setting, but they may learn at a slower pace than other children. Schools are responsible for providing an appropriate education for retarded children. Many teachers and parents feel that the practice of mainstreaming, or inclusion, which places such children in standard classrooms for at least part of the day, helps them to feel more a part of society and helps others to better understand their special needs and capabilities.


Many cases of mental retardation are now prevented by improved health care. Vaccines against rubella and measles prevent an estimated 3,000 cases of mental retardation in the United States yearly. Vaccination against Haemophilus influenzae b (Hib), a cause of childhood meningitis, is expected to prevent 3,000 more. Prevention of Rh disease (see Rh factor), screening and treatment for phenylketonuria, and emphasis on prenatal care and the dangers of poor nutrition or alcohol consumption during pregnancy have also resulted in a decrease in cases of mental retardation in the United States. Mental retardation rates in poor nations, however, are rising.


The treatment of mentally retarded people has always reflected the changes in society. They have been officially referred to as idiots and as the feebleminded. The introduction of the IQ test was followed by a classification system that used such terms as moron (IQ of 51–70), imbecile (26–50), and idiot (0–25); later these terms were softened and classifications redefined somewhat to mild (IQ of 55–70), moderate (40–54), severe (25–39), and profound (0–24) retardation. The term mentally retarded itself, although still commonly used, has been replaced in some settings by the term developmentally disabled.

Mentally retarded people have been subjected to unnecessary institutionalization and, as a result of the eugenics movement, involuntary sterilization. The deinstitutionalization movement of the 1970s reflected a concern for the civil rights of mentally retarded. Very few of the mentally retarded are now institutionalized; most now live independently, with their families, or in group homes. The emphasis on education and self-sufficiency seen in the late 20th cent. mirrors a similar movement in the 1840s.


See M. Adams, Mental Retardation and Its Social Dimensions (1971); A. Clarke et al., ed., Mental Retardation: The Changing Outlook (1985); E. Zigler, Understanding Mental Retardation (1986); American Association on Mental Retardation, Mental Retardation: Definition, Classification, and Systems of Support (1992).

The Columbia Encyclopedia, 6th ed. Copyright© 2013, The Columbia University Press.

Selected full-text books and articles on this topic

Understanding Mental Retardation
Patricia Ainsworth; Pamela Baker.
University Press of Mississippi, 2004
Intellectual Disability: Understanding Its Development, Causes, Classification, Evaluation, and Treatment
James C. Harris.
Oxford University Press, 2006
Deinstitutionalization and People with Intellectual Disabilities: In and out of Institutions
Kelley Johnson; Rannveig Traustadóttir.
Jessica Kingsley, 2005
We're People First: The Social and Emotional Lives of Individuals with Mental Retardation
Elaine E. Castles.
Praeger Publishers, 1996
Personality and Motivational Differences in Persons with Mental Retardation
Harvey N. Switzky.
Lawrence Erlbaum Associates, 2001
Career Development for Adolescents and Young Adults with Mental Retardation
Wadsworth, John; Milsom, Amy; Cocco, Karen.
Professional School Counseling, Vol. 8, No. 2, December 2004
Attitudes regarding Interpersonal Relationships with Persons with Mental Illness and Mental Retardation
Gordon, Phyllis A.; Tantillo, Jennifer Chiriboga; Feldman, David; Perrone, Kristin.
The Journal of Rehabilitation, Vol. 70, No. 1, January-March 2004
Recent Advances in the Diagnosis and Treatment of Attention-Deficit/hyperactivity Disorder in Individuals with Intellectual Disability
Huang, Haojiang; Ruedrich, Stephen.
Mental Health Aspects of Developmental Disabilities, Vol. 10, No. 4, October-December 2007
Ellis' Handbook of Mental Deficiency, Psychological Theory and Research
William E. MacLean Jr.
Lawrence Erlbaum Associates, 1997 (3rd edition)
Librarian’s tip: Part II "Contemporary Psychological Perspectives on Mental Retardation"
Emerging Issues in Mental Retardation: Self-Determination versus Self-Interest
Keigher, Sharon M.
Health and Social Work, Vol. 25, No. 3, August 2000
Service Problems and Solutions for Individuals with Mental Retardation and Metal Illness. (2001 NRA Graduate Literary Award Winner)
VanderSchie-Bezyak, Jill L.
The Journal of Rehabilitation, Vol. 69, No. 1, January-March 2003
Care or Custody? Mentally Disordered Offenders in the Criminal Justice System
Judith M. Laing.
Oxford University Press, 1999
Sterilization of People with Mental Disabilities: Issues, Perspectives, and Cases
Ellen Brantlinger.
Auburn House, 1995
Feeble-Minded in Our Midst: Institutions for the Mentally Retarded in the South, 1900-1940
Steven Noll.
University of North Carolina Press, 1995
Mental Retardation as a Bar to the Death Penalty: Who Bears the Burden of Proof?
Eftink, James Gerard.
Missouri Law Review, Vol. 75, No. 2, Spring 2010
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