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Decline in The General Ability Index (GAI) Score

By Inderbir Kaur Sandhu, Ph.D


Q: My son has taken the WISC-IV twice... once at age 6 and once at age 10. The first time he took it, he received a GAI score of 144. The second time, he received a GAI score of 133. Is this type of variance normal? What does it mean?

A: Briefly, the GAI (from WISC-IV) provides an estimate of general cognitive ability that is less sensitive to the influence of working memory and processing speed. In the WISC-IV, this may be used as a substitute for Full Scale IQ (FSIQ) to determine eligibility for programmes. Due to the fact that the processing speed index (PSI) and working memory index (WMI) of the WISC-IV are not the best indicators of intellectual ability, it is disregarded when assessing for giftedness and it is not uncommon to only report the GAI.

The impact of neuropsychological problems related to working memory and/or processing speed deficiencies also calls for a GAI score rather than the FSIQ. For e.g.,
when assessing a child who presents with potential neuropsychological issues, the GAI may be useful to clarify interpretation.

IQ scores become relatively stable around 6 years of age and should not change significantly over time since stability increases with age. Having said that, no IQ score is 100% accurate and is an estimate of a child’s intellectual ability. Therefore, some amount of error variance is possible which may show variance in scores over time. A variance as much as 7 points across testing administrations is not uncommon.

In your case, the variance is rather large and I can understand the concern although without a detail breakdown of scores and comparison between the years, it is hard to determine the reason for such a drop. What may be possible here is the very reason the GAI score is used instead. There may be an underlying issue, which may have not been resolved and could have gone worse. Scores are still very high but perhaps you may want to see the tester again with both the scores (detailed) to see where the drop has been most significant. It may be an indication of a possible learning concern, which may have been undetected earlier. Or it could also be something as simple as the child not feeling up to it on the day of test, extreme anxiety, rapport with the tester, etc.

Do see the tester for a better interpretation or another psychologist familiar with the testing and scores. Best wishes!


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