Definition and Causes of Intellectual Disability

Part I:

The basis of the definition of the term

mentally retarded

can be found as far back as 1941 when Edgar Doll outlined six elements in which he used to classify mental retardation:

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(1) Social incompetence,

(2) due to mental sub-normality,

(3) which has been developmentally arrested,

(4) which obtains at maturity,

(5) is of constitutional origin, and

(6) is essentially incurable (Doll, 1941).

In 1959 the American Association on Mental Deficiency published an updated definition for the term

mental retardation

. The term was now referenced to a person’s general intellectual functioning being below average (in other words their Intelligence Quotient “IQ”). The definition also changed to indicate that the term refers to intellectual functioning that is obtained during the period of development of a child and hinders their adaptive skills (Heber, 1959). In 1975, Public Law 94-142 was passed giving all students with disabilities a free appropriate public educate (FAPE). Later PL 94-142 was amended to become known as the Individuals with Disabilities Education ACT (IDEA) and the definition of FAPE in IDEA has remained unchanged since 1975. Also known as the Education for All Handicapped Children Act, this law changed the arena of public education for handicapped children who up until this point in time were often denied access to education and opportunities to learn, particularly those who were labelled as

mentally retarded


In the 2013 form of the Diagnostic and Statistical Manual of Mental Disorders (DSM), the term

intellectual disability

substituted the term

mental retardation

. This was in part because of Rosa’s Law. Rosa’s Law was signed in October of 2010 by President Barrack Obama and mandated that the terms “mental retardation” and” mentally retarded” be stricken from federal records. Instead, these terms were replaced with “intellectual disability” and “individual with an intellectual disability” (“History”, n.d., para. 7).

In 2015, the American Psychiatric Association (APA) put out the eleventh version of the DSM and formally proposed that the name of the diagnosis be changed from “mental retardation” to an “intellectual developmental disorder.”  One of the qualifying criteria for the diagnosis would still be for a person to score at least two standard deviations below average, there would no longer be a hard IQ requirement of 70 or under. Now in addition to the deviation in IQ score, the diagnosis is also classified by deficits in functional and adaptive skills. The DSM-5 outlines

intellectual disabilities

as neuro-developmental disorders that start during a person’s early years and are characterized by intellectual complications as well as difficulties in conceptual, social, and practical areas of living (Committee, 2015). The DSM-5 diagnosis of an intellectual disability requires the fulfillment of the following criteria:

1. Discrepancies in intellectual functioning — “reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience”—established by evaluation and IQ testing (APA, 2013, p. 33);

2. Discrepancies in adaptive skills that considerably impede developmental and sociocultural standards for the individual’s independence; and

3. The commencement of these discrepancies during childhood (Committee, 2015).

Having changed throughout the years, the term

mentally retarded

has now evolved to become known as

intellectual disabilities

. The basic components of an

intellectual disability

are categorized by significant restrictions both in intellectual functioning (reasoning, learning, problem solving) and in adaptive behavior (Patel & Brown, 2017). These components can cover a variety of everyday social and practical skills. Usually this disability originates before the age of 18 unless a Traumatic Brain Injury has occurred.

Part II:

Traditionally based on the Intelligent Quotient (IQ), the classification of an intellectual disability has shifted throughout the years as other criteria have been examined and taken into account for the definition. Today’s definition is based now on IQ as well as mental capacity, such as reasoning, problem solving, learning and so on (Patel & Brown, 2017). The reason for the shift in terminology from mental retardation to intellectual disability has several justifications. One of the main justifications for the shift in terminology is that the term

mental retardation

has become offensive to many people due to its negative connotations. The second justification for the shift in terminology is that former President Barrack Obama passed a law in 2010 that mandated all Federal agencies change all references of

mental retardation

to an

intellectual disability

. This was followed by the APA and the DSM-5 changing the formal definition of the qualifications for an intellectual disability.

Part III:

I live in a medium-ish size city in the South Eastern United States with a city population of 187,347 and 100% urban, 0% rural. Median household income is $35,816 per year in my city, $13,000 less than the average for our state. 25.4% of the population in my city live in poverty. Unemployment is currently at 3% in my city. A large state university of 25,000+ pumps out jobs and graduates for the local economy. The city is the world headquarters of Sea Ray Boats, Pilot Oil Corporation and Clayton Homes. We are twenty-five minutes west of one of the U.S. Departments of Energy’s largest facilities. 84% of the county has a high school diploma and 20% have at least a bachelor’s degree. Despite the large university, Department of Energy facility and major corporations’ bases, the stigma of the south east from the perception of the rest of the United States is that we are ignorant backwards bumpkins, an image that seems to be perpetuated in tv and movies.

Intellectual disabilities can be produced by any number of environmental and genetic factors. These factors can include: genetic conditions, problems that can occur during pregnancy, problems that can occur at birth, possible exposure to certain types of diseases or toxins, malnutrition or iodine deficiency. Given the poverty rate of approximately 25% and the lack of a college education being as high as it is, the possibility of malnutrition is a possibility for the region. Given the relative location of the city in relation to the U.S. Department of Energy’s location, there is a possibility of high levels of toxins being present in the air and water. These are supposedly monitored but anything is possible.

I do not believe that the levels of intellectual disability in my community are any higher than any other across the country. Levels of education are lower and teenage pregnancy rate is slightly higher than the national average but the occurrences of intellectual disability are still steady here.


  • APA (American Psychiatric Association). Diagnostic and statistical manual of mental disorders. fifth ed. Washington, DC: APA; 2013.
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  • Committee to Evaluate the Supplemental Security Income Disability Program for Children with Mental Disorders; Board on the Health of Select Populations; Board on Children, Youth, and Families; Institute of Medicine; Division of Behavioral and Social Sciences and Education; The National Academies of Sciences, Engineering, and Medicine; Boat TF, Wu JT, editors. Mental Disorders and Disabilities Among Low-Income Children. Washington (DC): National Academies Press (US); 2015 Oct 28. 9, Clinical Characteristics of Intellectual Disabilities. Available from:
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