To review the literature over the past decade on mental retardation, particularly as regards its definition, prevalence, major causes, and associated mental disorders.
A computerized search was performed for articles published in the past decade, and selected papers were highlighted.
The study of mental retardation has benefited considerably by advances in medicine generally and by developments in molecular neurobiology in particular. Increasing awareness of psychiatric comorbidity in the context of intellectual disability highlights the need for studies of the phenomenology and treatment of mental disorders in this population.
Although the study of developmental disorders has advanced significantly over the past decade, considerable work remains. Mental retardation is a model for the utility of the biopsychosocial approach in medicine.
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"However, some studies cite figures which are not even encompassed within this range, and it is acknowledged that the figures vary considerably depending on the classification criteria adopted, the survey methods used, the population being studied and the age range of the samples. For example, in their review of mental retardation in the US, King et al. (1997), cited figures for children aged 6 to 17 based on the US Department of Education database. While the overall figure was 11.4 per 1000, or just over one per cent, the range across the country varied by a factor of 10, extending from 3.2 per 1000 to 31.4 per 1000. "
[Show abstract][Hide abstract] ABSTRACT: For over a century the terminology and interpretation of learning difficulties has been subject to ongoing debate and change across all professions. This has resulted in considerable diversity within this field regarding definition and classification, and consequently also to issues in establishing prevalence rates. It is a field which has always been of central importance to educational psychologists. However, their relationship with this topic in terms of any agreed approach to definition, terminology and classification has been a somewhat uncertain one. This paper provides an overview of key issues arising in relation to learning difficulties, with a particular focus on those difficulties which may be described as severe and complex. A context is offered in which differences in approach to this subject across and within disciplines and across national boundaries may be understood and interpreted and prevalence rates estimated.
"More specifically, the AAID definition requires that the individual be deficient in two of ten adaptive functioning domains. However these domains were not empirically selected and reflect how much support an individual with ID requires to succeed in their everyday life rather then their level of cognitive impairment compared to a large normative population as determined by a standardized IQ score (Luckasson et al., 1992; King et al., 1997). However, if the definition of ID placed more weight on the individual's IQ level than on adaptive functioning, a universal IQ test would be required to ensure comparability of results. "
[Show abstract][Hide abstract] ABSTRACT: Currently Intellectual disability (ID) is classified as a Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) Intelligence Quotient (IQ) below 70 and an impairment in adaptive skills during the developmental period. We argue that because so many children/adults with ID have language based deficits, mental age comparison or matching of individuals from different ID groups or to a typically developing (TD) group should be according to their overall performance on a non-verbally based measure, such as the Raven's Coloured Progressive Matrices (RCPM). We suggest that the RCPM should replace the commonly used WISC-IV measure of intelligence, as a means of matching groups of ID and TD group on mental age as it is a better measure of reasoning ability in children with ID who invariably have verbally based deficits. In addition, we present evidence that RCPM mental aged matched children with low functioning Autism Spectrum Disorder (ASD), Down Syndrome (DS), idiopathic ID use different problem solving strategies than TD children, to achieve the same overall performance on the RCPM. This is presumably due to group difference in brain impairments as evidenced by brain imaging studies. We also present evidence from the literature that working memory is a major component of successful performance on an IQ test and impairment in working memory in ID could also affect problem solving abilities on the RCPM. The theoretical and educational implications of the discrepancy between similar overall performance level on an intelligence test, but different use of strategy are also explored.