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Disparity between the WISC IV Indices

By Inderbir Kaur Sandhu, Ph.D

Q: My daughter is a 10 year old (January) in fourth grade and was in the gifted program in Georgia from 1st grade until we moved last fall. She was put into the gifted program as a result of CogAt screening and Wechsler testing. When we relocated to the Chicago area last fall she had to start the gifted process over and was recently given the Wechsler IV in conjunction broad observations of behavior and academic performance.

She has always had a relative weakness in basic math functioning (usually between 80 - 90 percentile on any given measure) but performs much better with more complex items such as geometry. On the observation side her percentile rankings were: Key Math Diagnostic Arithmetic Test - Revised (96th basic concepts, 97th in applications), Wide Range Achievement Test 3rd Edition: Arithmetic (81), Wide Range Achievement Test 3rd Edition: Reading (99th), and was between 9th and 12th grade on the John's Basic Reading Inventory -- 9th independent and 12th instructional.

The real issue is with her FSIQ that came in at 123. Because of this she did not qualify for gifted services (130 needed). The question I have revolves around how she got the 123 FSIQ. Her Verbal Comprehension score was 130, Perceptual Reasoning of 135, Working Memory 99, and Processing Speed 97. She works slowly with a pencil and has always struggled with fine motor issues.

So the questions. Given the large disparity in VCI/PRI vs WMI/PSI should the GAI be used in this case? Also is this a signal of potential issues being masked by her overall high achievement?

A: It has been noticed that some of the Full Scale IQ scores on the WISC-IV are excessively lowered by Working Memory and Processing Speed scores, as is in the case of your daughter. Due to the fact that intelligence is primarily abstract reasoning ability, emphasis on short-term auditory memory and processing speed on paper-and-pencil tests is less helpful.

The GAI should be used in this case instead of the Full Scale IQ (FSIQ), since the four composite scores vary by 23 or more points, and as the Verbal Comprehension Index and the Perceptual Reasoning Index vary by less than 23 points. This may give fairer results. Somehow, it has been wrongly assumed that gifted children are fast processors. Some are really very quick in comparison to their non-gifted counterparts; however others may be quite reflective or perfectionistic - a trait that may slow down their speed. It has been indicated that of the four indices, the Verbal Comprehension Index is clearly the best indicator of giftedness and the Perceptual Reasoning Index is the second best indicator. For this reason it may be wise to administer only six of the subtests of the WISC-IV for selection to gifted programmes, which are Vocabulary, Similarities, Comprehension, Matrix Reasoning, Picture Concepts and Block Design. The General Ability Index (GAI) can be derived from these six subtests.

On potential issues masked by her overall high performance, a low WMI and PSI may point to attentional issues, which you may want to explore further. Another area is non verbal learning disorder, which can be marked with difficulties when it comes to executive functioning, poor visual motor skills and increased difficulties from a structured environment to a more abstract environment. Difficulties with visual processing may cause problems in integrating information, abstract thinking, math and aspects of comprehension.

Hope that helps. All the best.


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