Mental Retardation
347
(11-14-13)
Features of Mental Retardation
General:
Highly heterogeneous population: difficult to accurately characterize a "typical presentation"
Approximately 15-25% of cases have known, biological etiology
Male to female ratio approximately 1.5 to 1
Required Elements:
Significantly below average cognitive functioning
Significantly below average adaptive functioning
Developmental onset
Common Features:
Developmental delay
Socially responsive
Risk of behavior problems
Dekker and Koot (2003a, 2003b) examined a sample of Dutch children with intellectual disability and found comorbidity with psychiatric disorders and impairment high; many children with intellectual disability and psychiatric disorder do not receive mental health services
Need for special education
Occasional Features:
Need for structured caretaking environment throughout life
Neurological involvement
Unusual appearance
Interventions for mental retardation
Special education
Vocational habilitation
Development of adaptive skills & maximum participation in life
Psychological services
behavioral approaches
Two-Group Views of Mental Retardation
HYPOTHESIS: the total observed population of indiviuals with mental retardation represent a composite of two etiologically and functionally distinct populations.
various labels have been used:
"Organic"................................................. "Cultural-Familial"
"Pathological"......................................... "Normal variation"
"Moderate/Severe/Profound"................ "Mild"
IQ < 50...................................................... IQ > 50
Organic Mental Retardationknown biological cause of MR
usually moderate to profound retardation
no association with SES or ethnic group
greater association with physical disabilities
usually identified by parents/physician due to gross developmental delay/physical features
THEORY: child has been damaged by some powerful influenceCultural-Familial MR
no clear cause of retardation
usually mild MR
association with low SES & minority groups
no association with physical disabilities
associated with environmental deprivation
other family members may show MR
usually identified by teachers due to academic failure
THEORY: child reflects "normal" distribution of mental abilities, polygenetic influences on intelligence, negative environmental influencesGenetic influences in mental retardation:
familial risk and mental retardation
general population prevalence of MR: 1-2 %
both parents normal IQ but one
parent has sibling with MR: 13%
one parent has MR: 20%
both parents have MR: 42%Two-population models have generally received empirical support, but organic pathology cannot be identified in approximately 10% of citizens with severe MR and epilepsy, cerebral palsy, and other organic disorders are found more often in individuals with mild MR than in the general population.
Formulations of mental retardation
Development of Intellectual Testing
Francis Galton in England
theoretical model: genetic, unchangable
sensory & motor measures
Binet & Simon in France
The first successful attempt to measure human intelligence grew out of efforts to construct a "present state" measure of child's skills that would predict school success or failure:
the Binet-Simon scales
The child's performance in a wide variety of tasks similar to those observed in school were compared against children of a similar age.
The obtained "mental age" (MA)
was contrasted with the child's chronological age (CA)atheoretical
current performance measure
assess skills similar to those used in school
use average age group achievement as standard of comparison
Goddard at the Vineland Academy
Terman at Stanford University
Stanford-Binet, 5th Edition
David Wechsler and adult ability test
IQ Classifications based on WISC-III & WISC-IV
"superior" = 130 and above, app. 2% of population
"above average" = 120-129, app. 6% of population
"high average" = 110-119, app. 17% of population
"average" range = 90-109 , app. 50% of population
"low average" = 80-89, app. 16% of population
"borderline" = 70-79, app. 6% of population
"impaired" = less than 70, app. 2% of population
Mild 50-55 – app. 70: 85% of group, "educable"
Moderate 35-40 – 50-55: 10% of group, "trainable"
Severe 20-25 – 35-40:3-4% of group, "custodial"
Profound below 20-25:1-2% of group, "custodial"
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