Wechsler Intelligence Scale for Children-IV
General Ability Index
The General Ability Index (GAI) provides a measure of general cognitive ability, based on two of the four Factor Indexes that make
up the entire WISC-IV test. The GAI is comprised of the Verbal Comprehension Index and Perceptual Reasoning Index scores. Two
additional factors that comprise the WISC-IV Full Scale score are not part of the GAI: the Working Memory Index and Processing
Speed Index.
The rationale for using the GAI, rather than the Full Scale IQ score, is summarized in this conclusion from Who Are the Gifted Using
the New WISC-IV? by Linda Kreger Silverman, Ph.D., Barbara Gilman. M.S. and R. Frank Falk, Ph.D. from the Gifted Development
Center, Denver, Colorado:
“Studies conducted to date on the WISC-IV suggest that two of the four indices, the
Verbal Comprehension Index and the Perceptual Reasoning Index, provide the best
measures of giftedness. Therefore, it seems prudent to administer only 6 subtests of the
WISC-IV for selection to gifted programs: Vocabulary, Similarities, Comprehension,
Matrix Reasoning, Picture Concepts and Block Design. The General Ability Index (GAI)
can be derived from these six subtests, and is recommended by both the test publisher and
the new Essentials of WISC-IV Assessment by Flanagan and Kaufman (2004). They
advise using the GAI, instead of the Full Scale IQ.”
Subtests administered for the General Ability Index (GAI)
Verbal Comprehension Subtests
Perceptual Reasoning Subtests
Similarities
Block Design
Vocabulary
Picture Concepts
Comprehension
Matrix Reasoning
What each subtest measures:
Verbal Comprehension Index: A measure of verbal concept formation, verbal reasoning and knowledge acquired from one’s
environment.
Similarities – verbally expressed abstract associative reasoning. Student must explain how two things are related.
Vocabulary – a measure of the child’s word knowledge and ability to express the knowledge clearly.
Comprehension – a measure of verbal reasoning related to practical social situations. It involves knowledge of conventional
standards of behavior, social judgment and common sense reasoning.
Perceptual Reasoning Index: A measure of nonverbal perceptual and fluid reasoning and spatial processing.
Block Design – a measure of the ability to analyze and synthesize abstract visual stimuli, to use spatial reasoning to construct
block patterns to match a visual model.
Picture Concepts – a measure of abstract nonverbal categorical reasoning ability.
Matrix Reasoning – a measure of visual information processing and abstract nonverbal reasoning. There are 4 types of
matrices items that assess: simple to complex pattern completion, classification, analogical reasoning, and serial reasoning.