Tuesday, February 2, 2010

Some Observations on IQ Measurements in Williams Syndrome Patients

Intelligent Insights on Intelligence Theories and Tests (aka IQ's Corner): Intellectual heterogeneity of MR/ID as evidence against AAIDD "stuck on g" green manual: Even in cleary genetic-based syndromes (Williams Syndrome):

"I would argue, as have others, that this WS syndrome-specific cognitive stereotype is largely due to the fact that historically MR/ID researchers only had the V/P organized Wechsler batteries as their primary IQ battery...and that the 'profile' may be due to this research being constrained by batteries that did not validly measure a greater breadth of cognitive functioning. This is not a criticism of the past research, as researchers had limited theories of intelligence and measures of constructs from which to work. However, now that CHC theory has emerged as the consensus psychometric model of cognitive abilities and, more importantly, there are a significant number of well-standardized and psychometrically sound IQ batteries of multiple cognitive abilities, I'm not surprised that a syndrome with a strong genetic core, which typically results in more within-group similarity, when measured by more contemporary CHC-based IQ batteries display considerable variability/heterogeneity in patterns of cognitive abilities.

Below is the abstract for 2005 study that reported that WS individuals do NOT display the classic and historical syndrome-specific pattern of cognitive strengths and weaknesses when measured with a more contemporary CHC-based cognitive battery (WJ-R: conflict of interest note--I am a coauthor of the next edition..the WJ III).

This study clearly suggests that even a population of individuals with a shared genetic causal mechanism display significant individual differences in patterns of cognitive abilities. If this is found in ID/MR populations with a strong shared genetic causal mechanism, one would be hard-pressed to argue that such variability does not exist for more milder forms of ID/MR and the general population.

My point (again)---I'm very concerned that the AAIDD 11th Edition ID manual's 'stuck on g' position is out of synch with contemporary intelligence theory and measurement and has the potential to cause serious harm when potentially life-altering decisions are made on the basis of a single g-based composite IQ scores that ignores the heterogeneity of human cognitive abilities across the ability spectrum and different disorders.

Porter, M. A. & Coltheart, M. Cognitive Heterogeneity in Williams Syndrome. Developmental Neuropsychology, 27 (2), 275-306."

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