I'm a relative newbie to all this so someone PLEASE feel free to correct me.....here is what I think. The optional subtests are usually not given. My son was not given them. If there is an a priori reason to think a DC won't perform well on a test...say DC has writing issues, then the optional subtest will be administered. That score will be used for FSIQ. But this has to be done a priori. There is a file i downloaded at some point on the WISCIV stating the expected variance between the various subtests. For one of them, if there was greater than a 5pt difference between the 2 subtests scores, calculating the score for that was misleading. So if DC had a 5 coding and a 12 on the other PSI subtest, the final index score for PSI shouldn't be used. You would look at the individual indices instead as well as GAI. If the two subtest for each index measure the same thing ie VCI or PRI or WMI or PSI, you'd expect them to be close...if not, then one or the other is in error or signals some hidden disability.
