Wechsler Adult Intelligence Scale

Wechsler Adult Intelligence Scale or WAIS is a general test of intelligence (IQ), published in February 1955 as a revision of the Wechsler-Bellevue test (1939), a battery of tests that is composed from subtests Wechsler "adopted" from the Army Tests (Yerkes, 1921). Wechsler defined intelligence as "The global capacity of a person to act purposefully, to think rationally, and to deal effectively with his/her environment."^[1]

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Overview

The full scale IQ test is broken down into 14 sub tests, comprising the verbal (7 sub tests) and performance scales (7 sub tests).

Wechsler's tests provide three scores:

1. a verbal IQ (VIQ)
2. a performance IQ (PIQ)
3. a composite, single full-scale IQ score based on the combined scores.

WAIS-R was standardised in 1981 on a sample of 1,880 US subjects, ranging from 16 to 74 years of age, broken down into 9 different age groups. It is considered to have very strong reliability. The current version is WAIS-III (1997). WAIS-IV is currently undergoing national standardization and slated for release in late 2008.

The median full-scale IQ is centered at 100^[2], with a standard deviation of 15. In a normal distribution this IQ range (1σ above and below the mean) is where approximately 68% of adults would fall.

Test variants

The WAIS-III measure is appropriate throughout adulthood and for use with those individuals over 74 years of age. For persons under 16, the Wechsler Intelligence Scale for Children (WISC, 6-16 yrs) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI, 2 1/2-7yrs, 3mos) are used. An IQ score can be obtained without administering the verbal section of the test since each section yields its own score.

A short, four-subtest, version of the battery has recently been released, allowing clinicians to form a validated estimate of verbal, performance and full scale IQ in a shorter amount of time. The Wechsler Abbreviated Scale of Intelligence (WASI) uses the vocabulary, similarities, block design and matrix reasoning subtests of the WAIS to provide an estimate of the full IQ scores.

Intelligence tests also are used in populations with psychiatric illness or brain injury, though some regard this use as controversial. Some neuropsychologists use the technique on people suffering brain damage as it leads to links with which part of the brain has been affected, or use specific subtests in order to get an idea of the extent of the brain damage. For example, digit span may be used to get a sense of attentional difficulties. Others employ the WAIS-R NI (Wechsler Adult Intelligence Scale-Revised as a Neuropsychological Instrument), another measure published by Harcourt. Each subtest score is tallied and calculated with respect to non-normal or brain-damaged norms. As the WAIS is developed for the average, non-injured individual, separate norms were developed for appropriate comparison among similar functioning individuals^{[citation needed]}.

14 subtests of the WAIS-III

Verbal Subtests

Information 

Degree of general information acquired from culture (e.g. Who is the president of Russia?)

Comprehension

Ability to deal with abstract social conventions, rules and expressions (e.g. What does "Kill 2 birds with 1 stone" metaphorically mean?)

Arithmetic

Concentration while manipulating mental mathematical problems (e.g. How many 45c. stamps can you buy for a dollar?)

Similarities

Abstract verbal reasoning (e.g. In what way are an apple and a pear alike?)

Vocabulary

The degree to which one has learned, been able to comprehend and verbally express vocabulary (e.g. What is a guitar?)

Digit span

attention/concentration (e.g. given the sequence of digits '123', reverse the sequence.)

Letter-Number Sequencing

attention and working memory (e.g. Given Q1B3J2, place the numbers in numerical order and then the letters in alphabetical order)

Performance Subtests

Picture Completion

Ability to quickly perceive visual details

Digit Symbol - Coding

Visual-motor coordination, motor and mental speed

Block Design

Spatial perception, visual abstract processing & problem solving

Matrix Reasoning

Nonverbal abstract problem solving, inductive reasoning, spatial reasoning

Picture Arrangement

Logical/sequential reasoning, social insight

Symbol Search

Visual perception, speed

Object Assembly

Visual analysis, synthesis, and construction

Optional post-tests include Digit Symbol - Incidental Learning and Digit Symbol - Free Recall.

WAIS-III Subtests Grouped According to Indices

In addition to the Verbal and Performance IQ scores, the following four indices are derived.

Verbal comprehension

• Vocabulary

• Information

• Similarities

Perceptual organization

• Picture Completion
• Block Design
• Matrix Reasoning

Working memory

• Arithmetic
• Digit Span
• Letter-Number Sequencing

Processing speed

• Digit Symbol-Coding
• Symbol Search

Note: Picture Arrangement, Comprehension, and Object Assembly do not contribute to the Index Scores

See also

• David Wechsler
• Wechsler Intelligence Scale for Children (WISC)
• Wechsler Preschool and Primary Scale of Intelligence (WPPSI)
• IQ

References

1. ^ Weschler, David (1939). The measurement of adult intelligence. Baltimore: Williams & Wilkins, 229. 
2. ^ Distribution of IQ Scores. MSN Encarta. Retrieved on 2007-07-08.