Chapter 33
Intellectual Disability
300
, Chapter 33: Intellectual Disability
Introduction
In Ireland, most people currently describe either learning disability or intellectual disability. Other terms include
intellectual developmental disorder (DSM-V) and disorder of intellectual development (likely term in ICD-11).
These definitions in ICD and DSM are characterised by:
o Deficits in general mental abilities, including reasoning, problem-solving, planning (often assessed in IQ
performance).
o Significant limitations in one or more areas of adaptive behaviour across multiple environments.
o Limitations become apparent in childhood or adolescence.
Diagnosis of intellectual disability
o Involves use of standardised criteria (e.g. DSM-V or ICD-10), which include standardised assessments of both
intellectual ability and adaptive function.
o Intellectual ability
This is the sum of cognitive abilities that allow adaptation to the environment, including reasoning,
problem-solving, abstract thinking, comprehension and learning from experience.
Intelligence is commonly assessed with standardised tests resulting in an intelligence quotient (IQ) score
with a mean of 100 and standard deviation of 15 (e.g. Wechsler Intelligence Scale for Children [WISC-IV]
and the Stanford-Binet V).
o Adaptive function
This includes conceptual skills (e.g. communication, self-direction, money concepts), social skills and
practical skills (e.g. self-care, domestic skills, work, health skills).
Adaptive function correlates only moderately with intellectual ability.
Tests include the Vineland II Adaptive Behaviour Scales and the American Association on Mental
Retardation (AAMR) Adaptive Behaviour Scales.
Intellectual disability is classified as mild, moderate, severe or profound.
Those with an IQ just above the level of intellectual disability are often classified as having borderline intellectual
functioning.
Older terms are now inappropriate and often stigmatising (e.g. mental handicap, mental retardation, feeble-
minded).
World Health Organisation (WHO) uses functional definitions for a range of disabilities that are relevant:
o Impairment: fault in an organ system.
o Disability: loss of normal function for any human being.
o Handicap: social disadvantage accruing from the impairment and disability.
301
Intellectual Disability
300
, Chapter 33: Intellectual Disability
Introduction
In Ireland, most people currently describe either learning disability or intellectual disability. Other terms include
intellectual developmental disorder (DSM-V) and disorder of intellectual development (likely term in ICD-11).
These definitions in ICD and DSM are characterised by:
o Deficits in general mental abilities, including reasoning, problem-solving, planning (often assessed in IQ
performance).
o Significant limitations in one or more areas of adaptive behaviour across multiple environments.
o Limitations become apparent in childhood or adolescence.
Diagnosis of intellectual disability
o Involves use of standardised criteria (e.g. DSM-V or ICD-10), which include standardised assessments of both
intellectual ability and adaptive function.
o Intellectual ability
This is the sum of cognitive abilities that allow adaptation to the environment, including reasoning,
problem-solving, abstract thinking, comprehension and learning from experience.
Intelligence is commonly assessed with standardised tests resulting in an intelligence quotient (IQ) score
with a mean of 100 and standard deviation of 15 (e.g. Wechsler Intelligence Scale for Children [WISC-IV]
and the Stanford-Binet V).
o Adaptive function
This includes conceptual skills (e.g. communication, self-direction, money concepts), social skills and
practical skills (e.g. self-care, domestic skills, work, health skills).
Adaptive function correlates only moderately with intellectual ability.
Tests include the Vineland II Adaptive Behaviour Scales and the American Association on Mental
Retardation (AAMR) Adaptive Behaviour Scales.
Intellectual disability is classified as mild, moderate, severe or profound.
Those with an IQ just above the level of intellectual disability are often classified as having borderline intellectual
functioning.
Older terms are now inappropriate and often stigmatising (e.g. mental handicap, mental retardation, feeble-
minded).
World Health Organisation (WHO) uses functional definitions for a range of disabilities that are relevant:
o Impairment: fault in an organ system.
o Disability: loss of normal function for any human being.
o Handicap: social disadvantage accruing from the impairment and disability.
301
