Wechsler Adult Intelligence Scale-IV

The Wechsler Adult Intelligence Scale-IV (WAIS-IV) is the current version of the WAIS}} and was published in 2008. It superceded the [[WAIS-III which was published in 1997.

Outline
The WAIS-IV, is composed of 10 core subtests and five supplemental subtests, with the 10 core subtests comprising the Full Scale IQ. With the new WAIS-IV, the verbal/performance subscales from previous versions were removed and replaced by the index scores. The General Ability Index (GAI) was included, which consists of the Similarities, Vocabulary and Information subtests from the Verbal Comprehension Index and the Block Design, Matrix Reasoning and Visual Puzzles subtests from the Perceptual Reasoning Index. The GAI is clinically useful because it can be used as a measure of cognitive abilities that are less vulnerable to impairment.

Indexes and scales
There are four index scores representing major components of intelligence:
 * Verbal Comprehension Index (VCI)
 * Perceptual Reasoning Index (PRI)
 * Working Memory Index (WMI)
 * Processing Speed Index (PSI)

Two broad scores are also generated, which can be used to summarize general intellectual abilities:
 * Full Scale IQ (FSIQ), based on the total combined performance of the VCI, PRI, WMI, and PSI
 * General Ability Index (GAI), based only on the six subtests that comprise the VCI and PRI

Subtests
The Verbal Comprehension Index includes four tests:
 * 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?")
 * Information : Degree of general information acquired from culture (e.g., "Who is the president of Russia?")
 * Comprehension [Supplemental]: Ability to deal with abstract social conventions, rules and expressions (e.g., "What does Kill 2 birds with 1 stone metaphorically mean?")

The Perceptual Reasoning Index comprises five tests
 * Block Design: Spatial perception, visual abstract processing & problem solving
 * Matrix Reasoning: Nonverbal abstract problem solving, inductive reasoning, spatial reasoning
 * Visual Puzzles: non-verbal reasoning
 * Picture Completion [Supplemental]: Ability to quickly perceive visual details
 * Figure Weights [Supplemental]: quantitative and analogical reasoning

The Working Memory Index is obtained from three tests
 * Digit span: attention, concentration, mental control (e.g., Repeat the numbers 1-2-3 in reverse sequence)
 * Arithmetic: Concentration while manipulating mental mathematical problems (e.g., "How many 45-cent stamps can you buy for a dollar?")
 * Letter-Number Sequencing [Supplemental]: attention and working memory (e.g., Repeat the sequence Q-1-B-3-J-2, but place the numbers in numerical order and then the letters in alphabetical order)

The Processing Speed Index includes three tests
 * Symbol Search: Visual perception, speed
 * Coding: Visual-motor coordination, motor and mental speed
 * Cancellation [Supplemental]: visual-perceptual speed

Standardization
The WAIS-IV was standardized on a sample of 2,200 people in the United States ranging in age from 16 to 90. An extension of the standardization has been conducted with 688 Canadians in the same age range. The median Full Scale IQ is centered at 100, with a standard deviation of 15. In a normal distribution, the IQ range of one standard deviation above and below the mean (i.e, between 85 and 115) is where approximately 68% of all adults would fall.

WAIS-III
The WAIS-III was published in 1997. It provided scores for Verbal IQ, Performance IQ, and Full Scale IQ, along with four secondary indices (Verbal Comprehension, Working Memory, Perceptual Organization, and Processing Speed).

Verbal IQ (VIQ)
Included seven tests and provided two subindexes; verbal comprehension and working memory.

The Verbal comprehension index included the following tests:
 * Information
 * Similarities
 * Vocabulary

The Working memory index included:
 * Arithmetic
 * Digit Span
 * Letter-Number Sequencing

The seventh test; comprehension; was not included in any index

Performance IQ (PIQ)
Included seven tests and it also provided two subindexes; perceptual organization and processing speed.

The Perceptual organization index included:
 * Block Design
 * Matrix Reasoning
 * Picture Completion

The Processing speed index included:
 * Digit Symbol-Coding
 * Symbol Search

Two tests; Picture Arrangement and Object Assembly were not included in the indexes

Standardization
The WAIS-IV was standardized on a sample of 2,200 people in the United States ranging in age from 16 to 90. An extension of the standardization has been conducted with 688 Canadians in the same age range. The median Full Scale IQ is centered at 100, with a standard deviation of 15. In a normal distribution, the IQ range of one standard deviation above and below the mean (i.e, between 85 and 115) is where approximately 68% of all adults would fall.