Intellectual disability (ID), also known as general learning
disability, and mental retardation (MR), is a generalized
neurodevelopmental disorder characterized by significantly impaired
intellectual and adaptive functioning. It is defined by an IQ under 70
in addition to deficits in two or more adaptive behaviors that affect
everyday, general living.
Once focused almost entirely on cognition, the definition now includes
both a component relating to mental functioning and one relating to
individuals' functional skills in their environments. As a result of
this focus on the person's abilities in practice, a person with an
unusually low IQ may not be considered to have intellectually
Intellectual disability is subdivided into syndromic intellectual
disability, in which intellectual deficits associated with other
medical and behavioral signs and symptoms are present, and
non-syndromic intellectual disability, in which intellectual deficits
appear without other abnormalities.
Down syndrome and fragile X
syndrome are examples of syndromic intellectual disabilities.
Intellectual disability affects about 2–3% of the general
population. Seventy-five to ninety percent of the affected people
have mild intellectual disability. Non-syndromic or idiopathic
cases account for 30–50% of cases. About a quarter of cases are
caused by a genetic disorder, and about 5% of cases are inherited
from a person's parents. Cases of unknown cause affect about 95
million people as of 2013.
1 Signs and symptoms
3.1 Intelligence quotient
3.2 Distinction from other disabilities
3.3 Limitations in more than one area
6.1.1 United States
6.1.2 United Kingdom
7 Society and culture
8 Health disparities
9 See also
11 External links
Signs and symptoms
A historical image of a person with intellectual disability
Intellectual disability (ID) begins during childhood and involves
deficits in mental abilities, social skills, and core activities of
daily living (ADLs) when compared to same-aged peers. There often
are no physical signs of mild forms of ID, although there may be
characteristic physical traits when it is associated with a genetic
disorder (e.g., Down syndrome).
The level of impairment ranges in severity for each person. Some of
the early signs can include:
Delays in reaching or failure to achieve milestones in motor skills
development (sitting, crawling, walking)
Slowness learning to talk or continued difficulties with speech and
language skills after starting to talk
Difficulty with self-help and self-care skills (e.g., getting dressed,
washing, and feeding themselves)
Poor planning or problem solving abilities
Behavioral and social problems
Failure to grow intellectually or continued infant-like behavior
Problems keeping up in school
Failure to adapt or adjust to new situations
Difficulty understanding and following social rules
In early childhood, mild ID (IQ 50–69) may not be obvious or
identified until children begin school. Even when poor academic
performance is recognized, it may take expert assessment to
distinguish mild intellectual disability from specific learning
disability or emotional/behavioral disorders. People with mild ID are
capable of learning reading and mathematics skills to approximately
the level of a typical child aged nine to twelve. They can learn
self-care and practical skills, such as cooking or using the local
mass transit system. As individuals with intellectual disability reach
adulthood, many learn to live independently and maintain gainful
Moderate ID (IQ 35–49) is nearly always apparent within the first
years of life. Speech delays are particularly common signs of moderate
ID. People with moderate intellectual disability need considerable
supports in school, at home, and in the community in order to fully
participate. While their academic potential is limited, they can learn
simple health and safety skills and to participate in simple
activities. As adults, they may live with their parents, in a
supportive group home, or even semi-independently with significant
supportive services to help them, for example, manage their finances.
As adults, they may work in a sheltered workshop.
People with severe or profound ID need more intensive support and
supervision their entire lives. They may learn some ADLs, but an
intellectual disability is considered severe or profound when
individuals are unable to independently care for themselves without
ongoing significant assistance from a caregiver throughout
adulthood. Individuals with profound ID are completely dependent on
others for all ADLs and to maintain their physical health and safety,
although they may be able to learn to participate in some of these
activities to limited degree.
Further information: X-linked intellectual disability
Down syndrome is the most common genetic cause of intellectual
Among children, the cause of intellectual disability is unknown for
one-third to one-half of cases. About 5% of cases are inherited
from a person's parents. Genetic defects that cause intellectual
disability but are not inherited can be caused by accidents or
mutations in genetic development. Examples of such accidents are
development of an extra chromosome 18 (trisomy 18) and Down syndrome,
which is the most common genetic cause. Velocardiofacial syndrome
and fetal alcohol spectrum disorders are the two next most common
causes. However, doctors have found many other causes. The most
Genetic conditions. Sometimes disability is caused by abnormal genes
inherited from parents, errors when genes combine, or other reasons.
The most prevalent genetic conditions include Down syndrome,
Fragile X syndrome
Fragile X syndrome (common among boys),
neurofibromatosis, congenital hypothyroidism, Williams syndrome,
phenylketonuria (PKU), and Prader–Willi syndrome. Other genetic
conditions include Phelan-McDermid syndrome (22q13del), Mowat–Wilson
syndrome, genetic ciliopathy, and Siderius type X-linked
intellectual disability (OMIM 300263) as caused by mutations in the
PHF8 gene (OMIM 300560). In the rarest of cases, abnormalities
with the X or
Y chromosome may also cause disability.
48, XXXX and 49,
XXXXX syndrome affect a small number of girls worldwide, while boys
may be affected by 49, XXXXY, or 49, XYYYY. 47, XYY is not associated
with significantly lowered IQ though affected individuals may have
slightly lower IQs than non-affected siblings on average.
Problems during pregnancy.
Intellectual disability can result when the
fetus does not develop properly. For example, there may be a problem
with the way the fetus' cells divide as it grows. A pregnant person
who drinks alcohol (see fetal alcohol spectrum disorder) or gets an
infection like rubella during pregnancy may also have a baby with
Problems at birth. If a baby has problems during labor and birth, such
as not getting enough oxygen, he or she may have developmental
disability due to brain damage.
Exposure to certain types of disease or toxins. Diseases like whooping
cough, measles, or meningitis can cause intellectual disability if
medical care is delayed or inadequate. Exposure to poisons like lead
or mercury may also affect mental ability.
Iodine deficiency, affecting approximately 2 billion people
worldwide, is the leading preventable cause of intellectual disability
in areas of the developing world where iodine deficiency is endemic.
Iodine deficiency also causes goiter, an enlargement of the thyroid
gland. More common than full-fledged cretinism, as intellectual
disability caused by severe iodine deficiency is called, is mild
impairment of intelligence. Certain areas of the world due to natural
deficiency and governmental inaction are severely affected.
the most notorious, with 500 million suffering from deficiency,
54 million from goiter, and 2 million from cretinism. Among
other nations affected by iodine deficiency, China and
instituted widespread salt iodization programs, whereas, as of 2006,
Russia had not.
Malnutrition is a common cause of reduced intelligence in parts of the
world affected by famine, such as Ethiopia.
Absence of the arcuate fasciculus.
According to both the American Association on Intellectual and
Developmental Disabilities(Intellectual Disability: Definition,
Classification, and Systems of Supports (11th Edition) and the
American Psychiatric Association Diagnostic and Statistical Manual
of Mental Disorders (DSM-IV), three criteria must be met for a
diagnosis of intellectual disability: significant limitation in
general mental abilities (intellectual functioning), significant
limitations in one or more areas of adaptive behavior across multiple
environments (as measured by an adaptive behavior rating scale, i.e.
communication, self-help skills, interpersonal skills, and more), and
evidence that the limitations became apparent in childhood or
adolescence. In general, people with intellectual disability have an
IQ below 70, but clinical discretion may be necessary for individuals
who have a somewhat higher IQ but severe impairment in adaptive
It is formally diagnosed by an assessment of IQ and adaptive behavior.
A third condition requiring onset during the developmental period is
used to distinguish intellectual disability from other conditions
dementia such as
Alzheimer's disease or traumatic brain injuries.
The first English-language IQ test, the Stanford–Binet Intelligence
Scales, was adapted from a test battery designed for school placement
Alfred Binet in France.
Lewis Terman adapted Binet's test and
promoted it as a test measuring "general intelligence." Terman's test
was the first widely used mental test to report scores in
"intelligence quotient" form ("mental age" divided by chronological
age, multiplied by 100). Current tests are scored in "deviation IQ"
form, with a performance level by a test-taker two standard deviations
below the median score for the test-taker's age group defined as IQ
70. Until the most recent revision of diagnostic standards, an IQ of
70 or below was a primary factor for intellectual disability
diagnosis, and IQ scores were used to categorize degrees of
Since current diagnosis of intellectual disability is not based on IQ
scores alone, but must also take into consideration a person's
adaptive functioning, the diagnosis is not made rigidly. It
encompasses intellectual scores, adaptive functioning scores from an
adaptive behavior rating scale based on descriptions of known
abilities provided by someone familiar with the person, and also the
observations of the assessment examiner who is able to find out
directly from the person what he or she can understand, communicate,
and such like. IQ assessment must be based on a current test. This
enables diagnosis to avoid the pitfall of the Flynn effect, which is a
consequence of changes in population IQ test performance changing IQ
test norms over time.
Distinction from other disabilities
Clinically, intellectual disability is a subtype of cognitive deficit
or disabilities affecting intellectual abilities, which is a broader
concept and includes intellectual deficits that are too mild to
properly qualify as intellectual disability, or too specific (as in
specific learning disability), or acquired later in life through
acquired brain injuries or neurodegenerative diseases like dementia.
Cognitive deficits may appear at any age.
Developmental disability is
any disability that is due to problems with growth and development.
This term encompasses many congenital medical conditions that have no
mental or intellectual components, although it, too, is sometimes used
as a euphemism for intellectual disability.
Limitations in more than one area
Adaptive behavior, or adaptive functioning, refers to the skills
needed to live independently (or at the minimally acceptable level for
age). To assess adaptive behavior, professionals compare the
functional abilities of a child to those of other children of similar
age. To measure adaptive behavior, professionals use structured
interviews, with which they systematically elicit information about
persons' functioning in the community from people who know them well.
There are many adaptive behavior scales, and accurate assessment of
the quality of someone's adaptive behavior requires clinical judgment
as well. Certain skills are important to adaptive behavior, such as:
Daily living skills, such as getting dressed, using the bathroom, and
Communication skills, such as understanding what is said and being
able to answer
Social skills with peers, family members, spouses, adults, and others
By most definitions, intellectual disability is more accurately
considered a disability rather than a disease. Intellectual disability
can be distinguished in many ways from mental illness, such as
schizophrenia or depression. Currently, there is no "cure" for an
established disability, though with appropriate support and teaching,
most individuals can learn to do many things. Causes, such as
congenital hypothyroidism, if detected early may be treated to prevent
development of an intellectual disability.
There are thousands of agencies around the world that provide
assistance for people with developmental disabilities. They include
state-run, for-profit, and non-profit, privately run agencies. Within
one agency there could be departments that include fully staffed
residential homes, day rehabilitation programs that approximate
schools, workshops wherein people with disabilities can obtain jobs,
programs that assist people with developmental disabilities in
obtaining jobs in the community, programs that provide support for
people with developmental disabilities who have their own apartments,
programs that assist them with raising their children, and many more.
There are also many agencies and programs for parents of children with
Beyond that, there are specific programs that people with
developmental disabilities can take part in wherein they learn basic
life skills. These "goals" may take a much longer amount of time for
them to accomplish, but the ultimate goal is independence. This may be
anything from independence in tooth brushing to an independent
residence. People with developmental disabilities learn throughout
their lives and can obtain many new skills even late in life with the
help of their families, caregivers, clinicians and the people who
coordinate the efforts of all of these people.
There are four broad areas of intervention that allow for active
participation from caregivers, community members, clinicians, and of
course, the individual(s) with an intellectual disability. These
include psychosocial treatments, behavioral treatments,
cognitive-behavioral treatments, and family-oriented strategies.
Psychosocial treatments are intended primarily for children before and
during the preschool years as this is the optimum time for
intervention. This early intervention should include encouragement
of exploration, mentoring in basic skills, celebration of
developmental advances, guided rehearsal and extension of newly
acquired skills, protection from harmful displays of disapproval,
teasing, or punishment, and exposure to a rich and responsive language
environment. A great example of a successful intervention is the
Carolina Abecedarian Project that was conducted with over 100 children
from low SES families beginning in infancy through pre-school years.
Results indicated that by age 2, the children provided the
intervention had higher test scores than control group children, and
they remained approximately 5 points higher 10 years after the end of
the program. By young adulthood, children from the intervention group
had better educational attainment, employment opportunities, and fewer
behavioral problems than their control-group counterparts.
Core components of behavioral treatments include language and social
skills acquisition. Typically, one-to-one training is offered in which
a therapist uses a shaping procedure in combination with positive
reinforcements to help the child pronounce syllables until words are
completed. Sometimes involving pictures and visual aids, therapists
aim at improving speech capacity so that short sentences about
important daily tasks (e.g. bathroom use, eating, etc.) can be
effectively communicated by the child. In a similar fashion,
older children benefit from this type of training as they learn to
sharpen their social skills such as sharing, taking turns, following
instruction, and smiling. At the same time, a movement known as
social inclusion attempts to increase valuable interactions between
children with an intellectual disability and their non-disabled
peers. Cognitive-behavioral treatments, a combination of the
previous two treatment types, involves a strategical-metastrategical
learning technique[clarification needed] that teaches children math,
language, and other basic skills pertaining to memory and learning.
The first goal of the training is to teach the child to be a
strategical thinker through making cognitive connections and plans.
Then, the therapist teaches the child to be metastrategical by
teaching them to discriminate among different tasks and determine
which plan or strategy suits each task. Finally, family-oriented
strategies delve into empowering the family with the skill set they
need to support and encourage their child or children with an
intellectual disability. In general, this includes teaching
assertiveness skills or behavior management techniques as well as how
to ask for help from neighbors, extended family, or day-care
staff. As the child ages, parents are then taught how to approach
topics such as housing/residential care, employment, and
relationships. The ultimate goal for every intervention or technique
is to give the child autonomy and a sense of independence using the
acquired skills he/she has.
Although there is no specific medication for intellectual disability,
many people with developmental disabilities have further medical
complications and may be prescribed several medications. For example,
autistic children with developmental delay may be prescribed
antipsychotics or mood stabilizers to help with their behavior. Use of
psychotropic medications such as benzodiazepines in people with
intellectual disability requires monitoring and vigilance as side
effects occur commonly and are often misdiagnosed as behavioral and
Intellectual disability affects about 2–3% of the general
population. 75–90% of the affected people have mild intellectual
disability. Non-syndromic or idiopathic ID accounts for 30–50% of
cases. About a quarter of cases are caused by a genetic disorder.
Cases of unknown cause affect about 95 million people as of 2013.
It is more common in males and in low to middle income countries.
Intellectual disability has been documented under a variety of names
throughout history. Throughout much of human history, society was
unkind to those with any type of disability, and people with
intellectual disability were commonly viewed as burdens on their
Greek and Roman philosophers, who valued reasoning abilities,
disparaged people with intellectual disability as barely human.
The oldest physiological view of intellectual disability is in the
Hippocrates in the late fifth century BCE, who believed
that it was caused by an imbalance in the four humors in the brain.
Until the Enlightenment in Europe, care and asylum was provided by
families and the church (in monasteries and other religious
communities), focusing on the provision of basic physical needs such
as food, shelter and clothing. Negative stereotypes were prominent in
social attitudes of the time.
In the 13th century, England declared people with intellectual
disability to be incapable of making decisions or managing their
affairs. Guardianships were created to take over their financial
In the 17th century,
Thomas Willis provided the first description of
intellectual disability as a disease. He believed that it was
caused by structural problems in the brain. According to Willis, the
anatomical problems could be either an inborn condition or acquired
later in life.
In the 18th and 19th centuries, housing and care moved away from
families and towards an asylum model. People were placed by, or
removed from, their families (usually in infancy) and housed in large
professional institutions, many of which were self-sufficient through
the labor of the residents. Some of these institutions provided a very
basic level of education (such as differentiation between colors and
basic word recognition and numeracy), but most continued to focus
solely on the provision of basic needs of food, clothing, and shelter.
Conditions in such institutions varied widely, but the support
provided was generally non-individualized, with aberrant behavior and
low levels of economic productivity regarded as a burden to society.
Individuals of higher wealth were often able to afford higher degrees
of care such as home care or private asylums. Heavy
tranquilization and assembly line methods of support were the norm,
and the medical model of disability prevailed. Services were provided
based on the relative ease to the provider, not based on the needs of
the individual. A survey taken in 1891 in Cape Town, South Africa
shows the distribution between different facilities. Out of 2046
persons surveyed, 1,281 were in private dwellings, 120 in jails, and
645 in asylums, with men representing nearly two thirds of the number
surveyed. In situations of scarcity of accommodation, preference was
given to white men and black men (whose insanity threatened white
society by disrupting employment relations and the tabooed sexual
contact with white women).
In the late 19th century, in response to Charles Darwin's On the
Origin of Species,
Francis Galton proposed selective breeding of
humans to reduce intellectual disability. Early in the 20th
century the eugenics movement became popular throughout the world.
This led to forced sterilization and prohibition of marriage in most
of the developed world and was later used by
Adolf Hitler as a
rationale for the mass murder of people with intellectual disability
during the holocaust.
Eugenics was later abandoned as an evil
violation of human rights, and the practice of forced sterilization
and prohibition from marriage was discontinued by most of the
developed world by the mid-20th century.
Alfred Binet produced the first standardized test for
measuring intelligence in children.
Although ancient Roman law had declared people with intellectual
disability to be incapable of the deliberate intent to harm that was
necessary for a person to commit a crime, during the 1920s, Western
society believed they were morally degenerate.
Ignoring the prevailing attitude, Civitans adopted service to people
with developmental disabilities as a major organizational emphasis in
1952. Their earliest efforts included workshops for special education
teachers and daycamps for children with disabilities, all at a time
when such training and programs were almost nonexistent. The
segregation of people with developmental disabilities was not widely
questioned by academics or policy-makers until the 1969 publication of
Wolf Wolfensberger's seminal work "The Origin and Nature of Our
Institutional Models", drawing on some of the ideas proposed by SG
Howe 100 years earlier. This book posited that society characterizes
people with disabilities as deviant, sub-human and burdens of charity,
resulting in the adoption of that "deviant" role. Wolfensberger argued
that this dehumanization, and the segregated institutions that result
from it, ignored the potential productive contributions that all
people can make to society. He pushed for a shift in policy and
practice that recognized the human needs of those with intellectual
disability and provided the same basic human rights as for the rest of
The publication of this book may be regarded as the first move towards
the widespread adoption of the social model of disability in regard to
these types of disabilities, and was the impetus for the development
of government strategies for desegregation. Successful lawsuits
against governments and an increasing awareness of human rights and
self-advocacy also contributed to this process, resulting in the
passing in the U.S. of the Civil Rights of Institutionalized Persons
Act in 1980.
From the 1960s to the present, most states have moved towards the
elimination of segregated institutions. Normalization and
deinstitutionalization are dominant. Along with the work of
Wolfensberger and others including Gunnar and Rosemary Dybwad, a
number of scandalous revelations around the horrific conditions within
state institutions created public outrage that led to change to a more
community-based method of providing services.
By the mid-1970s, most governments had committed to
de-institutionalization, and had started preparing for the wholesale
movement of people into the general community, in line with the
principles of normalization. In most countries, this was essentially
complete by the late 1990s, although the debate over whether or not to
close institutions persists in some states, including
In the past, lead poisoning and infectious diseases were significant
causes of intellectual disability. Some causes of intellectual
disability are decreasing, as medical advances, such as vaccination,
increase. Other causes are increasing as a proportion of cases,
perhaps due to rising maternal age, which is associated with several
syndromic forms of intellectual disability.
Along with the changes in terminology, and the downward drift in
acceptability of the old terms, institutions of all kinds have had to
repeatedly change their names. This affects the names of schools,
hospitals, societies, government departments, and academic journals.
For example, the Midlands Institute of Mental Subnormality became the
British Institute of Mental Handicap and is now the British Institute
of Learning Disability. This phenomenon is shared with mental health
and motor disabilities, and seen to a lesser degree in sensory
The terms used for this condition are subject to a process called the
euphemism treadmill. This means that whatever term is chosen for this
condition, it eventually becomes perceived as an insult. The terms
mental retardation and mentally retarded were invented in the middle
of the 20th century to replace the previous set of terms, which
included "imbecile" and "moron" and are now considered
offensive. By the end of the 20th century, these terms themselves have
come to be widely seen as disparaging, politically incorrect, and in
need of replacement. The term intellectual disability is now
preferred by most advocates and researchers in most English-speaking
countries. As of 2015[update], the term "mental retardation" is
still used by the
World Health Organization
World Health Organization in the
ICD-10 codes, which
have a section titled "Mental Retardation" (codes F70–F79). In the
next revision, the ICD-11 is expected to replace the term mental
retardation with either intellectual disability or intellectual
developmental disorder, which the
DSM-5 already uses. Because
of its specificity and lack of confusion with other conditions, the
term "mental retardation" is still sometimes used in professional
medical settings around the world, such as formal scientific research
and health insurance paperwork.
The several traditional terms that long predate psychiatry are simple
forms of abuse in common usage today; they are often encountered in
such old documents as books, academic papers, and census forms. For
example, the British census of 1901 has a column heading including the
terms imbecile and feeble-minded.
Negative connotations associated with these numerous terms for
intellectual disability reflect society's attitude about the
condition. Some elements of society seek neutral medical terms, while
others want to use such terms as weapons of abuse.
Today, new expressions like developmentally disabled, special, or
challenged are replacing the term mentally retarded. The term
developmental delay is popular among caretakers and parents of
individuals with intellectual disability because delay suggests that a
person is slowly reaching his or her full potential rather than having
a lifelong condition.
Usage has changed over the years and differed from country to country.
For example, mental retardation in some contexts covers the whole
field but previously applied to what is now the mild MR group.
Feeble-minded used to mean mild MR in the UK, and once applied in the
US to the whole field. "Borderline intellectual functioning" is not
currently defined, but the term may be used to apply to people with
IQs in the 70s. People with IQs of 70 to 85 used to be eligible for
special consideration in the US public education system on grounds of
intellectual disability.
Cretin is the oldest and comes from a dialectal French word for
Christian. The implication was that people with significant
intellectual or developmental disabilities were "still human" (or
"still Christian") and deserved to be treated with basic human
dignity. Individuals with the condition were considered to be
incapable of sinning, thus "christ-like" in their disposition. This
term has not been used in scientific endeavors since the middle of the
20th century and is generally considered a term of abuse. Although
cretin is no longer in use, the term cretinism is still used to refer
to the mental and physical disability resulting from untreated
Amentia has a long history, mostly associated with dementia. The
difference between amentia and dementia was originally defined by time
of onset. Amentia was the term used to denote an individual who
developed deficits in mental functioning early in life, while dementia
included individuals who develop mental deficiencies as adults.
Theodor Meynert in the 1890s lectures described amentia as a form of
sudden-onset confusion (German: Verwirrtheit), often with
hallucinations. This term long in use in psychiatry in this sense.
Emil Kraepelin in the 1910s wrote that “acute confusion (amentia)”
is a form of febrile delirium. By 1912, amentia was a
classification lumping "idiots, imbeciles, and feeble minded"
individuals in a category separate from a dementia classification, in
which the onset is later in life. In Russian psychiatry the term
“amentia” defines a form of clouding of consciousness, which is
dominated by confusion, true hallucinations, incoherence of thinking
and speech and chaotic movements. In
(Russian: аменция) is not associated with intellectual
disability and mean only clouding of consciousness.
Idiot indicated the greatest degree of intellectual disability, where
the mental age is two years or less, and the person cannot guard
himself or herself against common physical dangers. The term was
gradually replaced by the term profound mental retardation (which has
itself since been replaced by other terms).
Imbecile indicated an intellectual disability less extreme than idiocy
and not necessarily inherited. It is now usually subdivided into two
categories, known as severe intellectual disability and moderate
Moron was defined by the American Association for the Study of the
Feeble-minded in 1910, following work by Henry H. Goddard, as the term
for an adult with a mental age between eight and twelve; mild
intellectual disability is now the term for this condition.
Alternative definitions of these terms based on IQ were also used.
This group was known in UK law from 1911 to 1959–60 as
Mongoloid idiot were medical terms used to identify
someone with Down syndrome, as the doctor who first described the
syndrome, John Langdon Down, believed that children with Down syndrome
shared facial similarities with Blumenbach's "Mongolian race." The
Mongolian People's Republic
Mongolian People's Republic requested that the medical community cease
use of the term as a referent to intellectual disability. Their
request was granted in the 1960s, when the World Health Organization
agreed that the term should cease being used within the medical
In the field of special education, educable (or "educable intellectual
disability") refers to ID students with IQs of approximately 50–75
who can progress academically to a late elementary level. Trainable
(or "trainable intellectual disability") refers to students whose IQs
fall below 50 but who are still capable of learning personal hygiene
and other living skills in a sheltered setting, such as a group home.
In many areas, these terms have been replaced by use of "moderate" and
"severe" intellectual disability. While the names change, the meaning
stays roughly the same in practice.
Retarded comes from the Latin retardare, "to make slow, delay, keep
back, or hinder," so mental retardation meant the same as mentally
delayed. The term was recorded in 1426 as a "fact or action of making
slower in movement or time." The first record of retarded in relation
to being mentally slow was in 1895. The term mentally retarded was
used to replace terms like idiot, moron, and imbecile because retarded
was not then a derogatory term. By the 1960s, however, the term had
taken on a partially derogatory meaning as well. The noun retard is
particularly seen as pejorative; a
BBC survey in 2003 ranked it as the
most offensive disability-related word, ahead of terms such as spastic
(or its abbreviation spaz) and mong. The terms mentally retarded
and mental retardation are still fairly common, but currently the
Special Olympics, Best Buddies, and over 100 other organizations are
striving to eliminate their use by referring to the word retard and
its variants as the "r-word", in an effort to equate it to the word
nigger and the associated euphemism "n-word", in everyday
conversation. These efforts have resulted in federal legislation,
sometimes known as "Rosa's Law", to replace the term mentally retarded
with the term intellectual disability in some federal
The term mental retardation was a diagnostic term denoting the group
of disconnected categories of mental functioning such as idiot,
imbecile, and moron derived from early IQ tests, which acquired
pejorative connotations in popular discourse. It acquired negative and
shameful connotations over the last few decades due to the use of the
words retarded and retard as insults. This may have contributed to its
replacement with euphemisms such as mentally challenged or
intellectually disabled. While developmental disability includes many
other disorders, developmental disability and developmental delay (for
people under the age of 18) are generally considered more polite terms
than mental retardation.
In North America, intellectual disability is subsumed into the broader
term developmental disability, which also includes epilepsy, autism,
cerebral palsy, and other disorders that develop during the
developmental period (birth to age 18). Because service provision is
tied to the designation 'developmental disability', it is used by many
parents, direct support professionals, and physicians. In the United
States, however, in school-based settings, the more specific term
mental retardation or, more recently (and preferably), intellectual
disability, is still typically used, and is one of 13 categories of
disability under which children may be identified for special
education services under Public Law 108-446.
The phrase intellectual disability is increasingly being used as a
synonym for people with significantly below-average cognitive ability.
These terms are sometimes used as a means of separating general
intellectual limitations from specific, limited deficits as well as
indicating that it is not an emotional or psychological disability. It
is not specific to congenital disorders such as Down syndrome.
The American Association on Mental Retardation changed its name to the
American Association on Intellectual and Developmental Disabilities
(AAIDD) in 2007, and soon thereafter changed the names of its
scholarly journals to reflect the term "intellectual disability."
In 2010, the AAIDD released its 11th edition of its terminology and
classification manual, which also used the term intellectual
In the UK, mental handicap had become the common medical term,
replacing mental subnormality in Scotland and mental deficiency in
England and Wales, until Stephen Dorrell, Secretary of State for
Health for the
United Kingdom from 1995–97, changed the NHS's
designation to learning disability. The new term is not yet widely
understood, and is often taken to refer to problems affecting
schoolwork (the American usage), which are known in the UK as
"learning difficulties." British social workers may use "learning
difficulty" to refer to both people with intellectual disability and
those with conditions such as dyslexia. In education, "learning
difficulties" is applied to a wide range of conditions: "specific
learning difficulty" may refer to dyslexia, dyscalculia or
developmental coordination disorder, while "moderate learning
difficulties", "severe learning difficulties" and "profound learning
difficulties" refer to more significant impairments.
In England and Wales between 1983 and 2008, the Mental Health Act 1983
defined "mental impairment" and "severe mental impairment" as "a state
of arrested or incomplete development of mind which includes
significant/severe impairment of intelligence and social functioning
and is associated with abnormally aggressive or seriously
irresponsible conduct on the part of the person concerned." As
behavior was involved, these were not necessarily permanent
conditions: they were defined for the purpose of authorizing detention
in hospital or guardianship. The term mental impairment was removed
from the Act in November 2008, but the grounds for detention remained.
However, English statute law uses mental impairment elsewhere in a
less well-defined manner—e.g. to allow exemption from
taxes—implying that intellectual disability without any behavioral
problems is what is meant.
BBC poll conducted in the
United Kingdom came to the conclusion that
'retard' was the most offensive disability-related word. On the
reverse side of that, when a contestant on Celebrity Big Brother live
used the phrase "walking like a retard", despite complaints from the
public and the charity Mencap, the communications regulator
not uphold the complaint saying "it was not used in an offensive
context [...] and had been used light-heartedly". It was, however,
noted that two previous similar complaints from other shows were
In the past, Australia has used British and American terms
interchangeably, including "mental retardation" and "mental handicap".
Today, "intellectual disability" is the preferred and more commonly
Society and culture
Severely disabled girl in Bhutan
People with intellectual disabilities are often not seen as full
citizens of society. Person-centered planning and approaches are seen
as methods of addressing the continued labeling and exclusion of
socially devalued people, such as people with disabilities,
encouraging a focus on the person as someone with capacities and gifts
as well as support needs. The self-advocacy movement promotes the
right of self-determination and self-direction by people with
intellectually disabilities, which means allowing them to make
decisions about their own lives.
Until the middle of the 20th century, people with intellectual
disabilities were routinely excluded from public education, or
educated away from other typically developing children. Compared to
peers who were segregated in special schools, students who are
mainstreamed or included in regular classrooms report similar levels
of stigma and social self-conception, but more ambitious plans for
employment. As adults, they may live independently, with family
members, or in different types of institutions organized to support
people with disabilities. About 8% currently live in an institution or
a group home.
In the United States, the average lifetime cost of a person with an
intellectual disability amounts to $1,014,000 per person, in 2003 US
dollars. This is slightly more than the costs associated with
cerebral palsy, and double that associated with serious vision or
hearing impairments. About 14% is due to increased medical expenses
(not including what is normally incurred by the typical person), 10%
is due to direct non-medical expenses, such as the excess cost of
special education compared to standard schooling, and 76% is indirect
costs accounting for reduced productivity and shortened lifespans.
Some expenses, such as costs associated with being a family caregiver
or living in a group home, were excluded from this calculation.
People with intellectual disability as a group have higher rates of
adverse health conditions such as epilepsy and neurological disorders,
gastrointestinal disorders, and behavioral and psychiatric problems
compared to people without disabilities. Adults also have a higher
prevalence of poor social determinants of health, behavioral risk
factors, depression, diabetes, and poor or fair health status than
adults without intellectual disability. In the United Kingdom
people with intellectual disability live on average 16 years less than
the general population.
History of psychiatric institutions
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FAQ on intellectual disabilities from the US Centers for Disease
Control's National Center on Birth Defects and Developmental
Rights, Law, Support
Convention on the Rights of Persons with Disabilities
Declaration on the Rights of Disabled Persons
International Classification of Functioning,
Disability and Health
Services for mental disorders
Services for the disabled
Structural and assistive
Activities of daily living
Orthotics and braces
Personal Care Assistant
Augmentative and alternative communication
Emotional and/or behavioral disability
Disability and religion
Disability and poverty
Disability and sexuality
22q11.2 deletion syndrome
Fragile X syndrome
Arts, media, culture, sport
Disability in the arts
Disability in the media
Mental and behavioral disorders (F00–F99 & 290–319)
Mild cognitive impairment
AIDS dementia complex
Organic brain syndrome
Psychoactive substances, substance abuse, drug abuse and
Schizophrenia, schizotypal and delusional
Psychosis and schizophrenia-like disorders
Brief reactive psychosis
Disorganized (hebephrenic) schizophrenia
Folie à deux
(Major depressive disorder
Seasonal affective disorder
Neurotic, stress-related and somatoform
Specific social phobia
Generalized anxiety disorder
(Acute stress reaction
Adjustment disorder with depressed mood
Body dysmorphic disorder
Da Costa's syndrome
Mass psychogenic illness
Dissociative identity disorder
(REM sleep behavior disorder
(Hypoactive sexual desire disorder
(Female sexual arousal disorder)
Adult personality and behavior
Sexual maturation disorder
Ego-dystonic sexual orientation
Sexual relationship disorder
Impulse control disorder
Disorders typically diagnosed in childhood
X-linked intellectual disability
Emotional and behavioral
(Separation anxiety disorder)
Symptoms and uncategorized
Intermittent explosive disorder
Psychogenic non-epileptic seizures