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The WISC-IV and Dyslexia

By Inderbir Kaur Sandhu, Ph.D


Q: My son aged 9 is dyslexic. He recently had his IQ tested . His FSIQ is 104 however his VCI is 126, PRI is 102, WMI is 27, and PSI is 13. There is a huge variation between the highest and lowest scores. Can the overall FSIQ be a true reflection of his capability given such huge variations in the scores of the individual tests? Many thanks.

A: The FSIQ (Full Scale IQ) score on the WISV-IV which represents overall cognitive ability, is derived from four other composite scores; the Verbal Comprehension index (VCI), Perceptual Reasoning Index (PRI), Processing Speed Index (PSI) and Working Memory Index (WMI). The FSIQ is generally a rather objective way to gauge general intellectual functioning of an individual. Your son scored in the superior range for VCI, with average on PRI; however, very low on both WMI and PSI.

When the variance between scores is small, I believe this procedure may be useful. However when there are considerable highs and extreme lows, as in the case of your son (what we sometimes call “a spiky profile” as seen on a graph), then the averaging of the scores may not be a reliable indicator. This is seen with students who may have a learning disability that affects one or more performance in any given intelligence test. The FSIQ is based on the average and would be brought down or up by extreme score that may not be reflective of the child's true intellectual abilities. Therefore, it is important to review individual scores rather than merely the FSIQ as it can discard specific information and the absence of such information can then give a false picture.

Also since the discrepancy is large, you may want to ask for a General Ability Index (GAI) score. Basically here only the VCI and the PRI is taken into account. There is some information on GAI score in the previous newsletters or you can do a search over the Internet.

Briefly, working memory is our ability to store and manipulate information for a short period. This is measured by dual-tasks, where the individual has to remember an item while simultaneously processing unrelated pieces of information. A widely used working memory task is the reading span task where the individual reads a sentence, verifies it, and then recalls the final word. Individual differences in working memory performance are closely related to a range of academic skills such as reading, spelling, comprehension, and mathematics.

Since your son has been diagnosed as dyslexic, his condition may have affected his processing speed and working memory. There have been many cases of dyslexics who scored lower on these. It could also be problem with visual processing and visual-motor integration that have an impact on processing speed. Visual motor issue may impact scores on subsets such as block design, symbol search and coding. Whatever the case is, low scores for both PSI and WMI are often indicators of a learning disability – in this case, we are sure of dyslexia - you may want to check if there is another concern.

No single test is a true reflection of a child's intelligence. It just captures what is being tested at that point in time. The Wechsler's series are indeed good tests for most but one would need someone with a lot of experience to interepret the scores. When interpret well for strengths and weaknesses, these tests can help children work on their weaker areas and enhance their strong points. All the best!


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