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Saturday, August 10, 2019

Human intelligence

From Wikipedia, the free encyclopedia
 
Human intelligence is the intellectual prowess of humans, which is marked by complex cognitive feats and high levels of motivation and self-awareness. Through their intelligence, humans possess the cognitive abilities to learn, form concepts, understand, apply logic, and reason, including the capacities to recognize patterns, comprehend ideas, plan, solve problems, make decisions, retain information, and use language to communicate.

Correlates

As a construct and measured by intelligence tests, intelligence is considered to be one of the most useful concepts used in psychology, because it correlates with lots of relevant variables, for instance the probability of suffering an accident, earning a higher salary, and more.
Education
According to a 2018 metastudy of educational effects on intelligence, education appears to be the "most consistent, robust, and durable method" known for raising intelligence.
Myopia
A number of studies have shown a correlation between IQ and myopia. Some suggest that the reason for the correlation is environmental, whereby intelligent people are more likely to damage their eyesight with prolonged reading, while others contend that a genetic link exists.
Aging
There is evidence that aging causes decline in cognitive functions. In one cross-sectional study, various cognitive functions measured declines by about 0.8 in z-score from age 20 to age 50, the cognitive functions included speed of processing, working memory and long term memory.

Theories

Relevance of IQ tests

In psychology, human intelligence is commonly assessed by IQ scores, determined by IQ tests. However, there are critics of IQ who do not dispute the stability of IQ test scores, or the fact that they predict certain forms of achievement rather effectively. They do argue, however, that to base a concept of intelligence on IQ test scores alone is to ignore many important aspects of mental ability.

On the other hand, Linda S. Gottfredson (2006) has argued that the results of thousands of studies support the importance of IQ for school and job performance (see also the work of Schmidt & Hunter, 2004). She says that IQ also predicts or correlates with numerous other life outcomes. In contrast, empirical support for non-g intelligences is lacking or very poor.

Theory of multiple intelligences

Howard Gardner's theory of multiple intelligences is based on studies not only of normal children and adults, but also of gifted individuals (including so-called "savants"), of persons who have suffered brain damage, of experts and virtuosos, and of individuals from diverse cultures. Gardner breaks intelligence down into at least a number of different components. In the first edition of his book Frames of Mind (1983), he described seven distinct types of intelligence—logical-mathematical, linguistic, spatial, musical, kinesthetic, interpersonal, and intrapersonal. In a second edition of this book, he added two more types of intelligence—naturalist and existential intelligences. He argues that psychometric (IQ) tests address only linguistic and logical plus some aspects of spatial intelligence. A major criticism of Gardner's theory is that it has never been tested, or subjected to peer review, by Gardner or anyone else, and indeed that it is unfalsifiable. Others (e.g. Locke, 2005) have suggested that recognizing many specific forms of intelligence (specific aptitude theory) implies a political—rather than scientific—agenda, intended to appreciate the uniqueness in all individuals, rather than recognizing potentially true and meaningful differences in individual capacities. Schmidt and Hunter (2004) suggest that the predictive validity of specific aptitudes over and above that of general mental ability, or "g", has not received empirical support. On the other hand, Jerome Bruner agreed with Gardner that the intelligences were "useful fictions," and went on to state that "his approach is so far beyond the data-crunching of mental testers that it deserves to be cheered."

Howard Gardner describes his first seven intelligences as follows:
  • Linguistic intelligence: People high in linguistic intelligence have an affinity for words, both spoken and written.
  • Logical-mathematical intelligence: It implies logical and mathematical abilities.
  • Spatial intelligence: The ability to form a mental model of a spatial world and to be able to maneuver and operate using that model.
  • Musical intelligence: Those with musical intelligence have excellent pitch, and may even be absolute pitch.
  • Bodily-kinesthetic intelligence: The ability to solve problems or to fashion products using one's whole body, or parts of the body. Gifted people in this intelligence may be good dancers, athletes, surgeons, craftspeople, and others.
  • Interpersonal intelligence: The ability to see things from the perspective of others, or to understand people in the sense of empathy. Strong interpersonal intelligence would be an asset in those who are teachers, politicians, clinicians, religious leaders, etc.
  • Intrapersonal intelligence: It is a capacity to form an accurate, veridical model of oneself and to be able to use that model to operate effectively in life.

Triarchic theory of intelligence

Robert Sternberg proposed the triarchic theory of intelligence to provide a more comprehensive description of intellectual competence than traditional differential or cognitive theories of human ability. The triarchic theory describes three fundamental aspects of intelligence. Analytic intelligence comprises the mental processes through which intelligence is expressed. Creative intelligence is necessary when an individual is confronted with a challenge that is nearly, but not entirely, novel or when an individual is engaged in automatizing the performance of a task. Practical intelligence is bound in a sociocultural milieu and involves adaptation to, selection of, and shaping of the environment to maximize fit in the context. The triarchic theory does not argue against the validity of a general intelligence factor; instead, the theory posits that general intelligence is part of analytic intelligence, and only by considering all three aspects of intelligence can the full range of intellectual functioning be fully understood. 

More recently, the triarchic theory has been updated and renamed as the Theory of Successful Intelligence by Sternberg. Intelligence is now defined as an individual's assessment of success in life by the individual's own (idiographic) standards and within the individual's sociocultural context. Success is achieved by using combinations of analytical, creative, and practical intelligence. The three aspects of intelligence are referred to as processing skills. The processing skills are applied to the pursuit of success through what were the three elements of practical intelligence: adapting to, shaping of, and selecting of one's environments. The mechanisms that employ the processing skills to achieve success include utilizing one's strengths and compensating or correcting for one's weaknesses. 

Sternberg's theories and research on intelligence remain contentious within the scientific community.

PASS theory of intelligence

Based on A. R. Luria's (1966) seminal work on the modularization of brain function, and supported by decades of neuroimaging research, the PASS Theory of Intelligence proposes that cognition is organized in three systems and four processes. The first process is the Planning, which involves executive functions responsible for controlling and organizing behavior, selecting and constructing strategies, and monitoring performance. The second is the Attention process, which is responsible for maintaining arousal levels and alertness, and ensuring focus on relevant stimuli. The next two are called Simultaneous and Successive processing and they involve encoding, transforming, and retaining information. Simultaneous processing is engaged when the relationship between items and their integration into whole units of information is required. Examples of this include recognizing figures, such as a triangle within a circle vs. a circle within a triangle, or the difference between 'he had a shower before breakfast' and 'he had breakfast before a shower.' Successive processing is required for organizing separate items in a sequence such as remembering a sequence of words or actions exactly in the order in which they had just been presented. These four processes are functions of four areas of the brain. Planning is broadly located in the front part of our brains, the frontal lobe. Attention and arousal are combined functions of the frontal lobe and the lower parts of the cortex, although the parietal lobes are also involved in attention as well. Simultaneous processing and Successive processing occur in the posterior region or the back of the brain. Simultaneous processing is broadly associated with the occipital and the parietal lobes while Successive processing is broadly associated with the frontal-temporal lobes. The PASS (Planning/Attention/Simultaneous/Successive) theory is heavily indebted to both Luria (1966, 1973), and studies in cognitive psychology involved in promoting a better look at intelligence.

Piaget's theory and Neo-Piagetian theories

In Piaget's theory of cognitive development the focus is not on mental abilities but rather on a child's mental models of the world. As a child develops, increasingly more accurate models of the world are developed which enable the child to interact with the world better. One example being object permanence where the child develops a model where objects continue to exist even when they cannot be seen, heard, or touched.

Piaget's theory described four main stages and many sub-stages in the development. These four main stages are:
  • sensory motor stage (birth-2yrs);
  • pre-operational stage (2yrs-7rs);
  • concrete operational stage (7rs-11yrs); and
  • formal operations stage (11yrs-16yrs)
Degree of progress through these stages are correlated, but not identical with psychometric IQ. Piaget conceptualizes intelligence as an activity more than a capacity. 

One of Piaget's most famous studies focused purely on the discriminative abilities of children between the ages of two and a half years old, and four and a half years old. He began the study by taking children of different ages and placing two lines of sweets, one with the sweets in a line spread further apart, and one with the same number of sweets in a line placed more closely together. He found that, "Children between 2 years, 6 months old and 3 years, 2 months old correctly discriminate the relative number of objects in two rows; between 3 years, 2 months and 4 years, 6 months they indicate a longer row with fewer objects to have "more"; after 4 years, 6 months they again discriminate correctly". Initially younger children were not studied, because if at the age of four years a child could not conserve quantity, then a younger child presumably could not either. The results show however that children that are younger than three years and two months have quantity conservation, but as they get older they lose this quality, and do not recover it until four and a half years old. This attribute may be lost temporarily because of an overdependence on perceptual strategies, which correlates more candy with a longer line of candy, or because of the inability for a four-year-old to reverse situations. By the end of this experiment several results were found. First, younger children have a discriminative ability that shows the logical capacity for cognitive operations exists earlier than acknowledged. This study also reveals that young children can be equipped with certain qualities for cognitive operations, depending on how logical the structure of the task is. Research also shows that children develop explicit understanding at age 5 and as a result, the child will count the sweets to decide which has more. Finally the study found that overall quantity conservation is not a basic characteristic of humans' native inheritance.

Piaget's theory has been criticized for the age of appearance of a new model of the world, such as object permanence, being dependent on how the testing is done (see the article on object permanence). More generally, the theory may be very difficult to test empirically because of the difficulty of proving or disproving that a mental model is the explanation for the results of the testing.

Neo-Piagetian theories of cognitive development expand Piaget's theory in various ways such as also considering psychometric-like factors such as processing speed and working memory, "hypercognitive" factors like self-monitoring, more stages, and more consideration on how progress may vary in different domains such as spatial or social.

Parieto-frontal integration theory of intelligence

Based on a review of 37 neuroimaging studies, Jung and Haier (2007) proposed that the biological basis of intelligence stems from how well the frontal and parietal regions of the brain communicate and exchange information with each other. Subsequent neuroimaging and lesion studies report general consensus with the theory. A review of the neuroscience and intelligence literature concludes that the parieto-frontal integration theory is the best available explanation for human intelligence differences.

Investment theory

Based on the Cattell–Horn–Carroll theory, the tests of intelligence most often used in the relevant studies include measures of fluid ability (Gf) and crystallized ability (Gc); that differ in their trajectory of development in individuals. The 'investment theory' by Cattell states that the individual differences observed in the procurement of skills and knowledge (Gc) are partially attributed to the 'investment' of Gf, thus suggesting the involvement of fluid intelligence in every aspect of the learning process. It is essential to highlight that the investment theory suggests that personality traits affect 'actual' ability, and not scores on an IQ test. In association, Hebb's theory of intelligence suggested a bifurcation as well, Intelligence A (physiological), that could be seen as a semblance of fluid intelligence and Intelligence B (experiential), similar to crystallized intelligence.

Intelligence compensation theory (ICT)

The intelligence compensation theory (a term first coined by Wood and Englert, 2009) states that individuals who are comparatively less intelligent work harder, more methodically, become more resolute and thorough (more conscientious) in order to achieve goals, to compensate for their 'lack of intelligence' whereas more intelligent individuals do not require traits/behaviours associated with the personality factor conscientiousness to progress as they can rely on the strength of their cognitive abilities as opposed to structure or effort. The theory suggests the existence of a causal relationship between intelligence and conscientiousness, such that the development of the personality trait conscientiousness is influenced by intelligence. This assumption is deemed plausible as it is unlikely that the reverse causal relationship could occur; implying that the negative correlation would be higher between fluid intelligence (Gf) and conscientiousness. The justification being the timeline of development of Gf, Gc and personality, as crystallized intelligence would not have developed completely when personality traits develop. Subsequently, during school-going ages, more conscientious children would be expected to gain more crystallized intelligence (knowledge) through education, as they would be more efficient, thorough, hard-working and dutiful.

This theory has recently been contradicted by evidence, that identifies compensatory sample selection. Thus, attributing the previous findings to the bias in selecting samples with individuals above a certain threshold of achievement.

Bandura's theory of self-efficacy and cognition

The view of cognitive ability has evolved over the years, and it is no longer viewed as a fixed property held by an individual. Instead, the current perspective describes it as a general capacity, comprising not only cognitive, but motivational, social and behavioural aspects as well. These facets work together to perform numerous tasks. An essential skill often overlooked is that of managing emotions, and aversive experiences that can compromise one's quality of thought and activity. The link between intelligence and success has been bridged by crediting individual differences in self-efficacy. Bandura's theory identifies the difference between possessing skills and being able to apply them in challenging situations. Thus, the theory suggests that individuals with the same level of knowledge and skill may perform badly, averagely or excellently based on differences in self-efficacy.

A key role of cognition is to allow for one to predict events and in turn devise methods to deal with these events effectively. These skills are dependent on processing of stimuli that is unclear and ambiguous. To learn the relevant concepts, individuals must be able to rely on the reserve of knowledge to identify, develop and execute options. They must be able to apply the learning acquired from previous experiences. Thus, a stable sense of self-efficacy is essential to stay focused on tasks in the face of challenging situations.

To summarize, Bandura's theory of self-efficacy and intelligence suggests that individuals with a relatively low sense of self-efficacy in any field will avoid challenges. This effect is heightened when they perceive the situations as personal threats. When failure occurs, they recover from it more slowly than others, and credit it to an insufficient aptitude. On the other hand, persons with high levels of self-efficacy hold a task-diagnostic aim that leads to effective performance.

Process, personality, intelligence and knowledge theory (PPIK)

Predicted growth curves for Intelligence as process, crystallized intelligence, occupational knowledge and avocational knowledge based on Ackerman's PPIK Theory.
 
Developed by Ackerman, the PPIK (process, personality, intelligence and knowledge) theory further develops the approach on intelligence as proposed by Cattell, the Investment theory and Hebb, suggesting a distinction between intelligence as knowledge and intelligence as process (two concepts that are comparable and related to Gc and Gf respectively, but broader and closer to Hebb's notions of "Intelligence A" and "Intelligence B") and integrating these factors with elements such as personality, motivation and interests.

Ackerman describes the difficulty of distinguishing process from knowledge, as content cannot be entirely eliminated from any ability test. Personality traits have not shown to be significantly correlated with the intelligence as process aspect except in the context of psychopathology. One exception to this generalization has been the finding of sex differences in cognitive abilities, specifically abilities in mathematical and spatial form. On the other hand, the intelligence as knowledge factor has been associated with personality traits of Openness and Typical Intellectual Engagement, which also strongly correlate with verbal abilities (associated with crystallized intelligence).

Latent inhibition

It appears that Latent inhibition can influence one's creativity.

Improving

Because intelligence appears to be at least partly dependent on brain structure and the genes shaping brain development, it has been proposed that genetic engineering could be used to enhance the intelligence, a process sometimes called biological uplift in science fiction. Experiments on mice have demonstrated superior ability in learning and memory in various behavioral tasks.

IQ leads to greater success in education, but independently education raises IQ scores. A 2017 meta-analysis suggests education increases IQ by 1-5 points per year of education, or at least increases IQ test taking ability.

Attempts to raise IQ with brain training have led to increases on aspects related with the training tasks – for instance working memory – but it is yet unclear if these increases generalise to increased intelligence per se.

A 2008 research paper claimed that practicing a dual n-back task can increase fluid intelligence (Gf), as measured in several different standard tests. This finding received some attention from popular media, including an article in Wired. However, a subsequent criticism of the paper's methodology questioned the experiment's validity and took issue with the lack of uniformity in the tests used to evaluate the control and test groups. For example, the progressive nature of Raven's Advanced Progressive Matrices (APM) test may have been compromised by modifications of time restrictions (i.e., 10 minutes were allowed to complete a normally 45-minute test). 

Substances which actually or purportedly improve intelligence or other mental functions are called nootropics. A meta analysis shows omega 3 fatty acids improves cognitive performance among those with cognitive deficits, but not among healthy subjects. A meta-regression shows omega 3 fatty acids improve the moods of patients with major depression (major depression is associated with mental deficits). However, exercise, not just performance-enhancing drugs, enhances cognition for healthy and non healthy subjects as well.

On the philosophical front, conscious efforts to influence intelligence raise ethical issues. Neuroethics considers the ethical, legal and social implications of neuroscience, and deals with issues such as the difference between treating a human neurological disease and enhancing the human brain, and how wealth impacts access to neurotechnology. Neuroethical issues interact with the ethics of human genetic engineering

Transhumanist theorists study the possibilities and consequences of developing and using techniques to enhance human abilities and aptitudes. 

Eugenics is a social philosophy which advocates the improvement of human hereditary traits through various forms of intervention. Eugenics has variously been regarded as meritorious or deplorable in different periods of history, falling greatly into disrepute after the defeat of Nazi Germany in World War II.

Measuring

Chart of IQ Distributions on 1916 Stanford-Binet Test
Score distribution chart for sample of 905 children tested on 1916 Stanford-Binet Test
 
The approach to understanding intelligence with the most supporters and published research over the longest period of time is based on psychometric testing. It is also by far the most widely used in practical settings. Intelligence quotient (IQ) tests include the Stanford-Binet, Raven's Progressive Matrices, the Wechsler Adult Intelligence Scale and the Kaufman Assessment Battery for Children. There are also psychometric tests that are not intended to measure intelligence itself but some closely related construct such as scholastic aptitude. In the United States examples include the SSAT, the SAT, the ACT, the GRE, the MCAT, the LSAT, and the GMAT. Regardless of the method used, almost any test that requires examinees to reason and has a wide range of question difficulty will produce intelligence scores that are approximately normally distributed in the general population.

Intelligence tests are widely used in educational, business, and military settings because of their efficacy in predicting behavior. IQ and g (discussed in the next section) are correlated with many important social outcomes—individuals with low IQs are more likely to be divorced, have a child out of marriage, be incarcerated, and need long-term welfare support, while individuals with high IQs are associated with more years of education, higher status jobs and higher income. Intelligence is significantly correlated with successful training and performance outcomes, and IQ/g is the single best predictor of successful job performance.

General intelligence factor or g

There are many different kinds of IQ tests using a wide variety of test tasks. Some tests consist of a single type of task, others rely on a broad collection of tasks with different contents (visual-spatial, verbal, numerical) and asking for different cognitive processes (e.g., reasoning, memory, rapid decisions, visual comparisons, spatial imagery, reading, and retrieval of general knowledge). The psychologist Charles Spearman early in the 20th century carried out the first formal factor analysis of correlations between various test tasks. He found a trend for all such tests to correlate positively with each other, which is called a positive manifold. Spearman found that a single common factor explained the positive correlations among tests. Spearman named it g for "general intelligence factor". He interpreted it as the core of human intelligence that, to a larger or smaller degree, influences success in all cognitive tasks and thereby creates the positive manifold. This interpretation of g as a common cause of test performance is still dominant in psychometrics. (Although, an alternative interpretation was recently advanced by van der Maas and colleagues. Their mutualism model assumes that intelligence depends on several independent mechanisms, none of which influences performance on all cognitive tests. These mechanisms support each other so that efficient operation of one of them makes efficient operation of the others more likely, thereby creating the positive manifold.) 

IQ tasks and tests can be ranked by how highly they load on the g factor. Tests with high g-loadings are those that correlate highly with most other tests. One comprehensive study investigating the correlations between a large collection of tests and tasks has found that the Raven's Progressive Matrices have a particularly high correlation with most other tests and tasks. The Raven's is a test of inductive reasoning with abstract visual material. It consists of a series of problems, sorted approximately by increasing difficulty. Each problem presents a 3 x 3 matrix of abstract designs with one empty cell; the matrix is constructed according to a rule, and the person must find out the rule to determine which of 8 alternatives fits into the empty cell. Because of its high correlation with other tests, the Raven's Progressive Matrices are generally acknowledged as a good indicator of general intelligence. This is problematic, however, because there are substantial gender differences on the Raven's, which are not found when g is measured directly by computing the general factor from a broad collection of tests.

General collective intelligence factor or c

A recent scientific understanding of collective intelligence, defined as a group's general ability to perform a wide range of tasks, expands the areas of human intelligence research applying similar methods and concepts to groups. Definition, operationalization and methods are similar to the psychometric approach of general individual intelligence where an individual's performance on a given set of cognitive tasks is used to measure intelligence indicated by the general intelligence factor g extracted via factor analysis. In the same vein, collective intelligence research aims to discover a ‘c factor’ explaining between-group differences in performance as well as structural and group compositional causes for it.

Historical psychometric theories

Several different theories of intelligence have historically been important for psychometrics. Often they emphasized more factors than a single one like in g factor.

Cattell–Horn–Carroll theory

Many of the broad, recent IQ tests have been greatly influenced by the Cattell–Horn–Carroll theory. It is argued to reflect much of what is known about intelligence from research. A hierarchy of factors for human intelligence is used. g is at the top. Under it there are 10 broad abilities that in turn are subdivided into 70 narrow abilities. The broad abilities are:
  • Fluid intelligence (Gf): includes the broad ability to reason, form concepts, and solve problems using unfamiliar information or novel procedures.
  • Crystallized intelligence (Gc): includes the breadth and depth of a person's acquired knowledge, the ability to communicate one's knowledge, and the ability to reason using previously learned experiences or procedures.
  • Quantitative reasoning (Gq): the ability to comprehend quantitative concepts and relationships and to manipulate numerical symbols.
  • Reading & writing ability (Grw): includes basic reading and writing skills.
  • Short-term memory (Gsm): is the ability to apprehend and hold information in immediate awareness and then use it within a few seconds.
  • Long-term storage and retrieval (Glr): is the ability to store information and fluently retrieve it later in the process of thinking.
  • Visual processing (Gv): is the ability to perceive, analyze, synthesize, and think with visual patterns, including the ability to store and recall visual representations.
  • Auditory processing (Ga): is the ability to analyze, synthesize, and discriminate auditory stimuli, including the ability to process and discriminate speech sounds that may be presented under distorted conditions.
  • Processing speed (Gs): is the ability to perform automatic cognitive tasks, particularly when measured under pressure to maintain focused attention.
  • Decision/reaction time/speed (Gt): reflect the immediacy with which an individual can react to stimuli or a task (typically measured in seconds or fractions of seconds; not to be confused with Gs, which typically is measured in intervals of 2–3 minutes).
Modern tests do not necessarily measure of all of these broad abilities. For example, Gq and Grw may be seen as measures of school achievement and not IQ. Gt may be difficult to measure without special equipment. 

g was earlier often subdivided into only Gf and Gc which were thought to correspond to the nonverbal or performance subtests and verbal subtests in earlier versions of the popular Wechsler IQ test. More recent research has shown the situation to be more complex.

Controversies

While not necessarily a dispute about the psychometric approach itself, there are several controversies regarding the results from psychometric research.

One criticism has been against the early research such as craniometry. A reply has been that drawing conclusions from early intelligence research is like condemning the auto industry by criticizing the performance of the Model T.

Several critics, such as Stephen Jay Gould, have been critical of g, seeing it as a statistical artifact, and that IQ tests instead measure a number of unrelated abilities. The American Psychological Association's report "Intelligence: Knowns and Unknowns" stated that IQ tests do correlate and that the view that g is a statistical artifact is a minority one.

Intelligence across cultures

Psychologists have shown that the definition of human intelligence is unique to the culture that one is studying. Robert Sternberg is among the researchers who have discussed how one's culture affects the person's interpretation of intelligence, and he further believes that to define intelligence in only one way without considering different meanings in cultural contexts may cast an investigative and unintentionally egocentric view on the world. To negate this, psychologists offer the following definitions of intelligence:
  1. Successful intelligence is the skills and knowledge needed for success in life, according to one's own definition of success, within one's sociocultural context.
  2. Analytical intelligence is the result of intelligence's components applied to fairly abstract but familiar kinds of problems.
  3. Creative intelligence is the result of intelligence's components applied to relatively novel tasks and situations.
  4. Practical intelligence is the result of intelligence's components applied to experience for purposes of adaption, shaping and selection.
Although typically identified by its western definition, multiple studies support the idea that human intelligence carries different meanings across cultures around the world. In many Eastern cultures, intelligence is mainly related with one's social roles and responsibilities. A Chinese conception of intelligence would define it as the ability to empathize with and understand others — although this is by no means the only way that intelligence is defined in China. In several African communities, intelligence is shown similarly through a social lens. However, rather than through social roles, as in many Eastern cultures, it is exemplified through social responsibilities. For example, in the language of Chi-Chewa, which is spoken by some ten million people across central Africa, the equivalent term for intelligence implies not only cleverness but also the ability to take on responsibility. Furthermore, within American culture there are a variety of interpretations of intelligence present as well. One of the most common views on intelligence within American societies defines it as a combination of problem-solving skills, deductive reasoning skills, and Intelligence quotient (IQ), while other American societies point out that intelligent people should have a social conscience, accept others for who they are, and be able to give advice or wisdom.

Friday, August 9, 2019

Intellectual disability

From Wikipedia, the free encyclopedia
 
Intellectual disability
Other namesIntellectual developmental disability (IDD), general learning disability
A child runs through the finishing line
Children with intellectual disabilities or other developmental conditions can compete in the Special Olympics.
SpecialtyPsychiatry, pediatrics
Frequency153 million (2015)

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 an individual's functional skills in their daily environment. As a result of this focus on the person's abilities in practice, a person with an unusually low IQ may still not be considered to have intellectual disability.

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 these 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.

Signs and symptoms

A historical image of a person with intellectual disability
 
Intellectual disability (ID) becomes apparent 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 employment.

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 (IQ 20–34) or Profound ID (IQ 19 or below) need more intensive support and supervision for 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. They may be able to learn to participate in some of these activities to limited degree.

Causes

An eight-year-old boy
Down syndrome is the most common genetic cause of intellectual disability.
 
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, there are many other causes. The most common are:

Diagnosis

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 functioning.

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, such as traumatic brain injuries and dementias (including Alzheimer's disease).

Intelligence quotient

The first English-language IQ test, the Stanford–Binet Intelligence Scales, was adapted from a test battery designed for school placement by 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 intellectual disability. 

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:

Management

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 developmental disabilities.

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 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 psychiatric problems.

Epidemiology

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.

History

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 families.

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 writings of Hippocrates in the late fifth century BCE, who believed that it was caused by an imbalance in the four humors in the brain.

Caliph Al-Walid (r. 705–715) built one of the first care homes for intellectually disabled individuals and built the first hospital which accommodated intellectually disabled individuals as part of its services. In addition, Al-Walid assigned each intellectually disabled individual a caregiver.

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 affairs.

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.
In 1905, 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 population.

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 Massachusetts.

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 disabilities.

Terminology

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.

The term "mental retardation" was used in the American Psychiatric Association's DSM-IV (1994) and in the World Health Organization's ICD-10 (codes F70–F79). In the next revision, the ICD-11, this term has been replaced by the term "disorders of intellectual development" (codes 6A00–6A04; 6A00.Z for the "unspecified" diagnosis code). The term "intellectual disability (intellectual developmental disorder)" is used in DSM-5 (2013). As of 2013, "intellectual disability (intellectual developmental disorder)" is the term that has come into common use by among educational, psychiatric, and other professionals over the past two decades. 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.

Vaguer expressions like developmentally disabled, special, or challenged have been used instead of the term mentally retarded. The term developmental delay was 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 congenital hypothyroidism.
  • 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 was 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 Russia “amentia” (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 intellectual disability.
  • 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 feeble-minded.
  • Mongolism and 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 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 community.
  • 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 statutes.
    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.

United States

Special Olympics USA team in July 2019
  • 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 disability.

United Kingdom

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.

A 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 Ofcom did 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 upheld.

Australia

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 used descriptor.

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 $223,000 per person, in 2003 US dollars, for direct costs such as medical and educational expenses. The indirect costs were estimated at $771,000, due to shorter lifespans and lower than average economic productivity. The total direct and indirect costs, which amount to a little more than a million dollars, are slightly more than the economic costs associated with cerebral palsy, and double that associated with serious vision or hearing impairmentss. Of the costs, about 14% is due to increased medical expenses (not including what is normally incurred by the typical person), and 10% is due to direct non-medical expenses, such as the excess cost of special education compared to standard schooling. The largest amount, 76%, is indirect costs accounting for reduced productivity and shortened lifespans. Some expenses, such as ongoing costs to family caregivers or the extra costs associated with living in a group home, were excluded from this calculation.

Health disparities

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.

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