Originally Posted by KADmom
Then I still don't understand why, for instance, my ds's tester considered the GAI to be the best measure in ds's report, when the tester also stated perfectionism most likely being behind the PSI score.

It's ultimately the discretion of the tester, but there are a number of guidelines between Pearson's http://pearsonassessmentsupport.com/support/index.php?View=download&EntryID=353 and this article+research from the Gifted Development Center http://www.gifteddevelopment.com/About_GDC/whoaregiftd.htm .