This article has some points to consider that tie into the discussion. Keep in mind it's about the WISC III and not the WISC-IV.
http://www.gifteddevelopment.com/PDF_files/tstresults.pdfSecond, discrepancies among subtest scores are much greater among the gifted than among any other group. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 1994), which establishes the criteria used by mental health professionals for various diagnoses, provides clear admonition against averaging subtest scores when they are highly discrepant.
When there is significant scatter in the subtest scores, the profile of strengths and weaknesses, rather than the mathematically derived full-scale IQ, will more accurately reflect the person�s learning abilities. When there is a marked discrepancy across verbal and performance scores, averaging to obtain a full-scale IQ score can be misleading. (p. 40)
This advice appears in the DSM-IV under the section on mental retardation. We recommend that the same caveat be used with the gifted. When discrepancies among subtest scores exceed 9 points, or when Verbal IQ and Performance IQ scores vary 15 or more points, the child�s strengths and weaknesses should be discussed separately rather
than averaged. The strengths should be used as the best indication of the child�s giftedness.
There are many nuances in both testing and test interpretation with the gifted that are not common knowledge. False positives are very unlikely: scores in the gifted range do not occur "accidentally" because one can�t fake abstract reasoning (Silverman, 1986). However, false negatives are abundant. Many more children are gifted than test in the gifted range. Underestimation of gifted children�s abilities, unfortunately, is much more common than accurate appraisal. When the examiner knows enough about giftedness to recognize this inherent danger in testing, all test results are subjected to confirmation with other data. If, for example, a child�s reading achievement score is 160, but the IQ score is 125, the IQ score must be an underestimate. It is impossible for a child to achieve beyond his or her capabilities. (This is why "overachiever" is an oxymoron.) Therefore, we recommend that the highest indicator of a child�s abilities at any age should be seen as the best estimate of the child�s giftedness. When other measures fall short of this indicator, the examiner needs to search carefully to determine possible causes of the underestimate.
Bottomline:
In the end, diagnosis of the degree of a child�s advancement must be based upon clinical judgment, not just on psychometric data.
