Determining FSIQ from GAI score
By Inderbir Kaur Sandhu, Ph.D
Is there a way to determine FSIQ from my son's GAI score on the WISC IV?
(He was given an individual test at 6.3 years)
His results were:
He was also given the Stanford Binet IV:
Quantitative Reasoning Index: 161
Quantitative SS: 150
Number Series SS: 160.
Unfortunately, this is not possible. The GAI (General Ability Index)
score only considers the VCI (verbal comprehension index) and the PRI
(perceptual reasoning index). For the Full Scale IQ, all 10 subtests are
required to calculate the FSIQ and the four Index scores are included in
the standard battery.
The GAI (VCI + PRI) is used in place of the FSIQ. When the FSIQ is not
interpretable, it has to be determined whether an abbreviated GAI may be
used to describe overall intellectual ability based on the following
If the answer is YES, then the GAI may be calculated and interpreted as
a reliable and valid estimate of a child's overall intellectual ability.
If the answer is NO, then the variation in the Indexes that compose the
GAI is too great (>23 points) for the purpose of summarising overall
ability in a single score (i.e., GAI).
In your son's case, it is a YES since the GAI score was calculated. The
following are the reason a tester may decide to use the GAI score and
not the FSIQ: There may be:
A significant and unusual discrepancy exists between VCI
A significant and unusual discrepancy exists between PRI
A significant and unusual discrepancy exists between WMI
and PSI, or
A significant and unusual subtest discrepancy between
subtests within WMI and/or PSI.
Hope the above helps. Please see the tester for further interpretation.
Best of luck!