The WISC-IV and Dyslexia
By Inderbir Kaur Sandhu, Ph.D
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.
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!