Percentile Difference on the WISC-IV
By Inderbir Kaur Sandhu, Ph.D
On the WISC-IV Canadian norms, my son scored 99.9 percentile
on General Ability.
On Verbal Comp. he scored 99.9 percentile.
On Perceptual Reasoning he scored 99 percentile.
Can you tell me what this means in terms of IQ? What's the
difference between 99 and 99.9 - and is it important. In our
area, the psychometric results don't attach an IQ number to
these percentiles, but at each teacher interview, I keep
hearing how, even in a class of Gifted Children, he is far
ahead yet he struggles with Math.....
From, Toronto - Ontario Canada
A: From the scores, it does
appear that your son is in the highly gifted range with such
high scores. Therefore, he would surely need special
attention. I believe that the tester used General Ability
Index, GAI instead of
Full Scale IQ (please refer to another reader's query on
GAI) to remove
the processing speed and working memory which may be
affected if a child struggles with Math. GAI is a composite
score that is based on Verbal Comprehension and Perceptual
Reasoning subtests, and does not include the Working Memory
or Processing Speed subtests which is included in the (FSIQ).
An IQ score is not attached to the percentile but the
detailed interpretation should have the full scale IQ which
gives a general idea of the child's IQ based on the test
taken. In your case, there should be a score for GAI. You
may want to find out from the tester.
The percentile is based on chronological age. It indicates a
child's standing as compared to other children of same age
group. According to the WISC technical reports, percentile
ranks reflect points on a scale at or below which a given
percentage of scores lie, based on the standardization
sample. In this case, say, a score of 99 percentile
indicates that your son's score is better than 99 per cent
of the sample that was tested (this makes the norms).
document may help you understand the WISC Canadian Norms
You should discuss the interpretation of his detailed
results with an educational psychologist who may be able to
test if he has any other learning difficulties that affects
his Math. Once any deficiency is found, intervention would
be necessary to lessen the struggle and improve learning.
Here's wishing you all the best in bringing up this very bright child!
Essentials of WISC-IV Assessment
Dawn P. Flanagan Ph.D, Alan S. Kaufman Ph.D
The WISC-IV is the top intelligence assessment instrument
for children in the US, providing essential information into
a child's cognitive functioning. This book applies a new,
expanded theory-based approach to interpreting the latest
edition of the WISCŪ and provides beginning and seasoned
clinicians with comprehensive step-by-step guidelines to
administering, scoring, and interpreting this latest
revision of the Wechsler Intelligence Scale for Children.
This book provides students and practitioners with an
unparalleled resource for learning and application,
including expert assessment of the test's relative strengths
and weaknesses, valuable advice on its clinical
applications, and illuminating case reports.