How to Calculate the GAI on the WISC

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Calculating the General Ability Index (GAI) on the Wechsler Intelligence Scale for Children WISC-III or WISC-IV (latest edition) is easier than it may first appear. As long as you have your child's full WISC test, you can calculate the score yourself -- no need to rely on a psychologist. The GAI score is derived only from the child's verbal and perceptual comprehension sub-tests of the full scale intelligence quotient (FSIQ). This score is important because it highlights certain aspects of cognitive ability necessary for advanced or gifted placement. Thus, schools often use this score to place children in different classes (e.g., gifted or special ed) or to predict future academic success.

Scoring the WISC

    The Block Design is one subtest that measures the GAI.
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    Calculate the scores for the sub-tests that determine the GAI score once the child has completed the full WISC. These sub-tests are: Vocabulary Comprehension, Similarities, Block Design, Matrix Reasoning and Picture Concepts.

    The vocabulary sub-test is one of the most important in measuring the GAI.
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    Add up the score for the Vocabulary Comprehension sub-test following the instructions in the WISC manual. Record the number of correct responses in the accompanying answer sheet.

    Add up the score for the Similarities sub-test following the instructions in the WISC manual. Record the number of correct responses in the accompanying answer sheet.

    The Block Design subtest measures perceptual reasoning.
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    Add up the score for the Block Design sub-test following the instructions in the WISC manual. Record the number of correct responses in the accompanying answer sheet.

    Add up the score for the Matrix Reasoning sub-test following the instructions in the WISC manual. Record the number of correct responses in the accompanying answer sheet.

    Record the correct responses for the Picture Concepts Subtest.
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    Add up the score for the Picture Concepts sub-test following the instructions in the WISC manual. Record the number of correct responses in the accompanying answer sheet.

Record the General Ability of Sum Scaled Scores

    Add up the subtests scores.
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    Add up all the scores and record in the WISC answer sheet once you have scored each of the sub-tests involved in the GAI score. You now have your GAI raw score which you need to convert into a percentage.

    Use the WISC manual to help you understand the GAI score.
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    Locate the General Ability Sum of Scaled Scores table in the book using the WISC manual. Scan horizontally for your child's raw score. Locate the GAI composite score, accompanying percentile rank and confidence interval.

    The GAI can determine classroom placement.
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    Write down the composite score, the percentile rank and the confidence interval (90% or 95%). This number will come in handy when you present your child for gifted or special education classes.

    Tips

    • Use a calculator to add up the sub-tests scores. This will result in less mistakes. Keep in mind that the GAI score is not your child's Full Scale IQ, but only a sub-component that specifically evaluates verbal and perceptual reasoning.

    Warnings

    • It is easy to miscalculate the GAI on the WISC-IV. Double check your math and the scaled sums before reporting the score to professionals or psychologists.

References

About the Author

Kathryn Wagner currently lives in Uganda. She has more than six years of professional writing experience and her poems and essays have appeared in "Nidus," "the North Dakota Quarterly," "Big City Lit," "Identity Theory" and the "Tucson Weekly." Wagner has a Master of Fine Arts in creative writing from the University of Arizona.

Photo Credits

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