Gifted Issues Discussion homepage Forums Identification, Testing & Assessment GAI calculation question

While reading about GAI calculations, I discovered that the percentile figure given by our psychologist is different from than that associated with DS7's scaled subtest scores. The applicable subtests add up to 87, which tracks to 135 and 99, while our tester said 97. Curious I calculated his FSIQ (not given in the report because of the gap btwn PS and everything else) and got 135. Which leads to two questions: 1. is there some subtlety I'm missing about the GAI calculation or should I be asking the psychologist to re-crunch the numbers; and 2. when the FSIQ is identical in spite of low processing speed, is it still necessary to use the GAI rather than the FSIQ?

I wouldn't worry about this except for the difficulty we're having in getting DS7's school to comprehend the test results as they stand. I'd hate to have their accuracy called into question (an administrator is already making noises about disbelieving the WJ-III results). Many thanks.

I'd suspect that the tester did something off unless you did. There really is not magic or subtlety to calculating the GAI. You just add up the scaled scores from all four indices and there it is.

In looking at the WISC technical report #4, though, a sum of scaled scores of 87 should give you a GAI of 132, which is the 98th percentile. The other thing I'm wondering on, though, is the FSIQ being 135 if the PSI index was significantly lower. I have one child with that type of profile and I am having a hard time imagining the FSIQ and GAI being identical in that instance. We saw something like a 7 point bump on the GAI over the FSIQ b/c PSI was average and the other three indices were in the upper 90s.

I totally understand if you don't want to post all scaled scores here, but overall something sounds a bit off.

We are, indeed, in Canada - I got 132/98 my first attempt, as well, and then realized there were different norms here (incidentally, do either of you know why?). I used the VC and PR scaled scores to get 87, per the tech report.

And yes, Dottie, that is exactly how I miscalculated the FSIQ! I thought it seemed too easy (and too unlikely given the average PS scores). Using the GAI makes perfect sense now!

Do either of you know if a layperson can calculate the percentiles for each category from the scaled scores? I'm now curious about the accuracy of those numbers...

Thank you both for your assistance!

Thanks, Dottie. The explanation is most helpful. I'm trying to fully understand the calculations, myself, so that I am more useful to DS7 when dealing with his school. And it's genuinely interesting, as well.

I would be very grateful to have the math checked. I just have scaled scores and they are:

VC: 16; 17; 13
PR: 14; 13; 14
WM: 13; 16
PS: 8; 11

He did other subtests, as well, but I understand those don't factor in to the overall calculations (is that right?). I can forward them if they are relevant.

Thanks so much.