Chapter 5 – Intellectual Disability (Intellectual Developmental Disorder)
Intellectual disability (ID): characterized by significant limitations in mental abilities (such as
reasoning, planning, and judgment) that result in impairments in adaptive functioning and
practical skills needed to fulfill aspects of everyday life.
Intelligence and intellectual disability
Eugenics: first defined by Sir Francis Galton (1883) as ‘the science which deals with all
influences that improve the inborn quality of race”.
General intellectual functioning: one’s general level of intellectual ability, defined, by an
intelligence quotient (IQ or equivalent) derived from an assessment with one or more of the
standardized, individually administered intelligence tests (such as Wechsler Intelligence Scales
for Children: WISC-V, the Stanford-Binet: SB5, and the Kaufman Assessment Battery for
Children: KABC-II).
• The tests asses various verbal and visual-spatial skills, and mathematical concepts.
Adaptive functioning: the ability to cope effectively with ordinary life demands, to live
independently, and to abide by community standards. Adaptive functioning is a necessary
component for defining levels of intellectual disability. 3 major categories of adaptive behavior:
1. Conceptual skills (reading/writing, receptive/expressive language)
2. Social skills (responsibility, self-esteem, follows rules, obeys laws)
3. Practical skills (eating, dressing, preparing meals, take medication, use transportation)
Intelligence and Intellectual Disability – Section Summary
- The early history of intellectual disability was plagued by ignorance and blame.
- By the mid-twentieth century, progress toward understanding intellectual disability moved more
rapidly, as parents, researchers, politicians, and the public sought better answers regarding its
causes and better ways to assist both children and adults with ID.
- Intellectual disability refers to limitations in both intelligence and adaptive behavior. However,
many persons with this disorder are capable of learning and of leading fulfilling lives.
- Despite its drawbacks, the IQ has become a principle standard for diagnosing intellectual
disability, combined with other skills and abilities of the child.
Features of intellectual disabilities
Clinical description
Most children with ID have difficulty with some aspect of learning. The degree of difficulty
depends on the extent of cognitive impairment, which is the primary reason current definitions
of intellectual disability emphasize this aspect.
3 core features of ID:
1. Individuals must have deficits in the intellectual functions of reasoning, problem-solving,
planning, abstract thinking, judgement, academic learning, and learning from experience.
2. Deficits in adaptive functioning, which result in failure to meet developmental and
sociocultural standard for personal independence and social responsibility.
3. The child’s intellectual and adaptive deficits must have begun during the developmental
period (before age 18.
4 levels of impairment: mild, moderate, severe or profound.
• Defined on the basis of adaptive functioning in 3 domains: conceptual, social and practical.
Mild intellectual disability: children with mild intellectual disability often show small delays in
development during the preschool years, but typically are not identified until academic or
behavior problems emerge during the early elementary years.
, Moderate intellectual disability: children/adolescents at this level of impairment are more
intellectually and adaptively impaired than someone with mild intellectual disability, and
usually they are identified during the preschool years, when they show delays in reaching early
developmental milestones.
Severe intellectual disability: most of these individuals suffer one or more organic causes of
impairment, such as genetic defects, and are identified at a very young age because they have
substantial delays in development and visible physical features or anomalies.
Profound intellectual disability: individuals with this disability are typically identified in infancy
because of marked delays in development and biological anomalies such as asymmetrical facial features.
Prevalence
• ID occurs in 1-3% of the general populations.
• More often in males than females.
• ID is more prevalent among children of lower socioeconomic status (SES) and children
from minority groups.
Features of Intellectual Disabilities – Section Summary
- The DSM-5 criteria for ID consist of deficits in intellectual functioning (confirmed by IQ testing
and clinical assessment), deficits in adaptive functioning, and onset of intellectual and adaptive
deficits during the developmental period.
- Children with ID vary widely in their degree of disability and level of functioning.
- IQ scores are no longer used to determine level of impairment. Rather, DSM-5 describes 4 levels
of severity – mild, moderate, sever, or profound – based on adaptive functioning that determines
a person’s level of needed supports.
- ID occurs in an estimated 1% of the population, more often among males than females.
- ID occurs more often among children from lower socioeconomic and minority groups. Economic
disadvantage and discrimination practices often account for these findings.
Developmental course and adult outcomes
Down syndrome: a chromosomal abnormality in which there are 3 copies of chromosome 21
rather than the normal 2. Children with Down syndrome typically function at the moderate level
of intellectual disability, having an increased likelihood of medical problems, and have unusual
physical features. This syndrome is also called trisomy 21.
Developmental-versus-difference controversy: a debate regarding the developmental
progression of children with mental impairments. The developmental position argues that all
children, regardless of intellectual impairments, progress through the same developmental
stages in the same sequence, but at different rates. The difference position argues that the
development of children with mental impairments proceeds in a different, less sequential, and
less organized fashion than that of children without impairments.
Down syndrome/ID:
• Down syndrome is the considerable delay in the expressive language development that
is necessary to establish independent living skills.
• Children with Down syndrome show delayed and aberrant functioning in their internal
state language, the language that reflects the emergent sense of self and others and is
critical for social interaction.
• Impulse control disorders, anxiety disorders, and mood disorders are the most
commonly diagnosed psychiatric diagnoses for children with ID.
• By early adulthood, persons with ID show a greater risk for psychopathology.
Intellectual disability (ID): characterized by significant limitations in mental abilities (such as
reasoning, planning, and judgment) that result in impairments in adaptive functioning and
practical skills needed to fulfill aspects of everyday life.
Intelligence and intellectual disability
Eugenics: first defined by Sir Francis Galton (1883) as ‘the science which deals with all
influences that improve the inborn quality of race”.
General intellectual functioning: one’s general level of intellectual ability, defined, by an
intelligence quotient (IQ or equivalent) derived from an assessment with one or more of the
standardized, individually administered intelligence tests (such as Wechsler Intelligence Scales
for Children: WISC-V, the Stanford-Binet: SB5, and the Kaufman Assessment Battery for
Children: KABC-II).
• The tests asses various verbal and visual-spatial skills, and mathematical concepts.
Adaptive functioning: the ability to cope effectively with ordinary life demands, to live
independently, and to abide by community standards. Adaptive functioning is a necessary
component for defining levels of intellectual disability. 3 major categories of adaptive behavior:
1. Conceptual skills (reading/writing, receptive/expressive language)
2. Social skills (responsibility, self-esteem, follows rules, obeys laws)
3. Practical skills (eating, dressing, preparing meals, take medication, use transportation)
Intelligence and Intellectual Disability – Section Summary
- The early history of intellectual disability was plagued by ignorance and blame.
- By the mid-twentieth century, progress toward understanding intellectual disability moved more
rapidly, as parents, researchers, politicians, and the public sought better answers regarding its
causes and better ways to assist both children and adults with ID.
- Intellectual disability refers to limitations in both intelligence and adaptive behavior. However,
many persons with this disorder are capable of learning and of leading fulfilling lives.
- Despite its drawbacks, the IQ has become a principle standard for diagnosing intellectual
disability, combined with other skills and abilities of the child.
Features of intellectual disabilities
Clinical description
Most children with ID have difficulty with some aspect of learning. The degree of difficulty
depends on the extent of cognitive impairment, which is the primary reason current definitions
of intellectual disability emphasize this aspect.
3 core features of ID:
1. Individuals must have deficits in the intellectual functions of reasoning, problem-solving,
planning, abstract thinking, judgement, academic learning, and learning from experience.
2. Deficits in adaptive functioning, which result in failure to meet developmental and
sociocultural standard for personal independence and social responsibility.
3. The child’s intellectual and adaptive deficits must have begun during the developmental
period (before age 18.
4 levels of impairment: mild, moderate, severe or profound.
• Defined on the basis of adaptive functioning in 3 domains: conceptual, social and practical.
Mild intellectual disability: children with mild intellectual disability often show small delays in
development during the preschool years, but typically are not identified until academic or
behavior problems emerge during the early elementary years.
, Moderate intellectual disability: children/adolescents at this level of impairment are more
intellectually and adaptively impaired than someone with mild intellectual disability, and
usually they are identified during the preschool years, when they show delays in reaching early
developmental milestones.
Severe intellectual disability: most of these individuals suffer one or more organic causes of
impairment, such as genetic defects, and are identified at a very young age because they have
substantial delays in development and visible physical features or anomalies.
Profound intellectual disability: individuals with this disability are typically identified in infancy
because of marked delays in development and biological anomalies such as asymmetrical facial features.
Prevalence
• ID occurs in 1-3% of the general populations.
• More often in males than females.
• ID is more prevalent among children of lower socioeconomic status (SES) and children
from minority groups.
Features of Intellectual Disabilities – Section Summary
- The DSM-5 criteria for ID consist of deficits in intellectual functioning (confirmed by IQ testing
and clinical assessment), deficits in adaptive functioning, and onset of intellectual and adaptive
deficits during the developmental period.
- Children with ID vary widely in their degree of disability and level of functioning.
- IQ scores are no longer used to determine level of impairment. Rather, DSM-5 describes 4 levels
of severity – mild, moderate, sever, or profound – based on adaptive functioning that determines
a person’s level of needed supports.
- ID occurs in an estimated 1% of the population, more often among males than females.
- ID occurs more often among children from lower socioeconomic and minority groups. Economic
disadvantage and discrimination practices often account for these findings.
Developmental course and adult outcomes
Down syndrome: a chromosomal abnormality in which there are 3 copies of chromosome 21
rather than the normal 2. Children with Down syndrome typically function at the moderate level
of intellectual disability, having an increased likelihood of medical problems, and have unusual
physical features. This syndrome is also called trisomy 21.
Developmental-versus-difference controversy: a debate regarding the developmental
progression of children with mental impairments. The developmental position argues that all
children, regardless of intellectual impairments, progress through the same developmental
stages in the same sequence, but at different rates. The difference position argues that the
development of children with mental impairments proceeds in a different, less sequential, and
less organized fashion than that of children without impairments.
Down syndrome/ID:
• Down syndrome is the considerable delay in the expressive language development that
is necessary to establish independent living skills.
• Children with Down syndrome show delayed and aberrant functioning in their internal
state language, the language that reflects the emergent sense of self and others and is
critical for social interaction.
• Impulse control disorders, anxiety disorders, and mood disorders are the most
commonly diagnosed psychiatric diagnoses for children with ID.
• By early adulthood, persons with ID show a greater risk for psychopathology.
