Originally Posted by JDAx3
So, PSI does have an impact and can 'skew' the results, if even just a bit.
In some cases it can skew the results significantly. That seems to be why the NAGC put out this position statement about USE OF THE WISC-IV FOR GIFTED IDENTIFICATION.
http://www.nagc.org/index.aspx?id=2455

It says in part:

Originally Posted by NAGC
Testers of the gifted know that abstract reasoning tasks best identify cognitive giftedness, while processing skills measures do not...
When the WISC-IV is used for the identification of gifted students, either the General Ability Index (GAI), which emphasizes reasoning ability, or the Full Scale IQ Score (FSIQ), should be acceptable for selection to gifted programs. The GAI should be derived using the table provided in the Harcourt Assessments website (Technical Report 4)