How To Calculate The GAI On The WISC

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.

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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.

Step 5

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.

Step 6

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.

Step 1

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.

Step 2

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.

Step 3

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.