Wechsler Adult Intelligence Scale

The WAIS is founded on Wechsler's definition of intelligence, which he defined as "... the global capacity of a person to act purposefully, to think rationally, and to deal effectively with his environment."[3] He believed that intelligence was made up of specific elements that could be isolated, defined, and subsequently measured. However, these individual elements were not entirely independent, but were all interrelated. His argument, in other words, is that general intelligence is composed of various specific and interrelated functions or elements that can be individually measured.[4]

This theory differed greatly from the Binet scale which, in Wechsler's day, was generally considered the supreme authority with regard to intelligence testing. A drastically revised new version of the Binet scale, released in 1937, received a great deal of criticism from David Wechsler (after whom the original Wechsler–Bellevue Intelligence scale and the modern Wechsler Adult Intelligence Scale IV are named).[4]

• Wechsler was a very influential advocate for the concept of non-intellective factors, and he felt that the 1937 Binet scale did not do a good job of incorporating these factors into the scale (non-intellective factors are variables that contribute to the overall score in intelligence, but are not made up of intelligence-related items. These include things such as lack of confidence, fear of failure, attitudes, etc.).
• Wechsler did not agree with the idea of a single score that the Binet test gave.[4]
• Wechsler argued that the Binet scale items were not valid for adult test-takers because the items were chosen specifically for use with children.[4]
• The "Binet scale's emphasis on speed, with timed tasks scattered throughout the scale, tended to unduly handicap older adults."[4]
• Wechsler believed that "mental age norms clearly did not apply to adults."[4]
• Wechsler criticized the then existing Binet scale because "it did not consider that intellectual performance could deteriorate as a person grew older."[4]

These criticisms of the 1937 Binet test helped produce the Wechsler–Bellevue scale, released in 1939. However, the present-day WAIS-IV has contradicted many of these criticisms, by incorporating a single overall score, using multiple timed tasks, focusing on intellective items and other ways. While this scale has been revised (resulting in the present day WAIS-IV), many of the original concepts Wechsler argued for, have become standards in psychological testing, including the point-scale concept and the performance-scale concept.[4]

The Wechsler–Bellevue tests were innovative in the 1930s because they:

1. gathered tasks created for nonclinical purposes for administration as a "clinical test battery",[5]
2. used the point scale concept instead of the age scale, and
3. included a non-verbal performance scale.[6][7]

The WAIS was initially created as a revision of the Wechsler–Bellevue Intelligence Scale (WBIS), which was a battery of tests published by Wechsler in 1939. The WBIS was composed of subtests that could be found in various other intelligence tests of the time, such as Robert Yerkes' army testing program and the Binet-Simon scale. The WAIS was first released in February 1955 by David Wechsler. Because the Wechsler tests included non-verbal items (known as performance scales) as well as verbal items for all test-takers, and because the 1960 form of Lewis Terman's Stanford–Binet Intelligence Scales was less carefully developed than previous versions, Form I of the WAIS surpassed the Stanford–Binet tests in popularity by the 1960s.[2]

The WAIS-R, a revised form of the WAIS, was released in 1981 and consisted of six verbal and five performance subtests. The verbal tests were: Information, Comprehension, Arithmetic, Digit Span, Similarities, and Vocabulary. The Performance subtests were: Picture Arrangement, Picture Completion, Block Design, Object Assembly, and Digit Symbol. A verbal IQ, performance IQ and full scale IQ were obtained.[9]

This revised edition did not provide new validity data, but used the data from the original WAIS; however new norms were provided, carefully stratified.[9]

The WAIS-III, a subsequent revision of the WAIS and the WAIS-R, was released 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).

The current version of the test, the WAIS-IV, which was released in 2008, is composed of 10 core subtests and five supplemental subtests, with the 10 core subtests yielding scaled scores that sum to derive the Full Scale IQ. With the WAIS-IV, the verbal/performance IQ scores 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 impairments of processing speed and working memory.

Index scores 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, which can be used to summarize general intellectual ability, can also be derived:

• 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 the VCI and PRI comprise.

WAIS-IV subtests grouped by index

Index	Subtest	Core?	Description	Proposed abilities measured
Verbal Comprehension	Similarities		Describe how two words or concepts are similar.	Abstract verbal reasoning; semantic knowledge
	Vocabulary		Name objects in pictures or define words presented to them.	Semantic knowledge; verbal comprehension and expression
	Information		General knowledge questions	Degree of general information acquired from culture
	Comprehension		Questions about social situations or common concepts.	Ability to express abstract social conventions, rules and expressions
Perceptual Reasoning	Block Design		Put together red-and-white blocks in a pattern according to a displayed model. This is timed, and some of the more difficult puzzles award bonuses for speed.	Visual spatial processing and problem solving; visual motor construction
	Matrix Reasoning		View an array of pictures with one missing square, and select the picture that fits the array from five options.	Nonverbal abstract problem solving, inductive reasoning
	Visual Puzzles		View a puzzle in a stimulus book and choose from among pieces of which three could construct the puzzle	Visual spatial reasoning
	Picture Completion		Select the missing part of a picture	Ability to quickly perceive visual details
	Figure Weights		View a stimulus book that pictures shapes on a scale (or scales) with one empty side and select the choice that keeps the scale balanced	Quantitative reasoning
Working Memory	Digit Span		Listen to sequences of numbers orally and to repeat them as heard, in reverse order, and in ascending order.	Working memory, attention, encoding, auditory processing
	Arithmetic		Orally administered arithmetic word problems. Timed.	Quantitative reasoning, concentration, mental manipulation
	Letter-Number Sequencing		Recall a series of numbers in increasing order and letters in alphabetical order.	Working memory, attention, mental control
Processing Speed	Symbol Search		View rows of symbols and target symbols, and mark whether or not the target symbols appear in each row.	Processing speed
	Coding		Transcribe a digit-symbol code using a key. The task is time-limited.	Processing speed, associative memory, graphomotor speed
	Cancellation		Scan arrangements of shapes and mark specific target shapes within a limited amount of time	Processing speed

The WAIS-IV measure is acceptable for use with people who are 16–90 years of age. For people younger than 16, the Wechsler Preschool and Primary Scale of Intelligence (WPPSI, 2½–7 years, 7 months) and the Wechsler Intelligence Scale for Children (WISC, 6–16 years) are used.[11]

Intelligence tests may be used to assess the level of cognitive functioning in individuals with psychiatric illness or brain injury. Rehabilitation psychologists and neuropsychologists use neuropsychological tests (including the WAIS-IV) to assess how the individual's brain is functioning after it has been injured. Specific subtests can provide insight into specific cognitive functions; for example, the digit span subtest could be used to look for attentional difficulties.[11]

The Wechsler tests can also be used to identify intellectual giftedness, and are commonly accepted as qualifying evidence for high-IQ societies, such as Mensa, Intertel and the Triple Nine Society.[12][13][14]

The Wechsler Abbreviated Scale of Intelligence - 2nd edition (WASI-II) is a short psychological test that was developed in 2011 by Pearson to estimate intellectual functioning in a shorter period of time than the WAIS-IV.[15] The WASI-II only has 4 subtests: Block Design, Vocabulary, Similarities, and Matrix Reasoning, compared to the 10 core subtests that are present in the WAIS-IV. These 4 subtests have the same structure as the similarly-named subtests on the WAIS-IV, but have different questions.

The WASI-II can derive 4 composite scores from a combination of the 4 subtests. A Verbal Comprehension Index (VCI) can be dervied from the raw scores on the Vocabulary and Similarities subtests. A Perceptual Reasoning Index (PRI) can be derived from the raw scores on the Matrix Reasoning and Block Design subtests. A Full Scale IQ-2 (FSIQ-2) can be derived from the raw scores on the Matrix Reasoning and Vocabulary subtests, while a Full Scale IQ-4 (FSIQ-4) can be derived from the raw scores on all 4 subtests.

WASI-II Subtests grouped by index

• Wechsler Intelligence Scale for Children
• Wechsler Preschool and Primary Scale of Intelligence

• Matarazzo, Joseph D. (1972). Wechsler's Measurement and Appraisal of Adult Intelligence (5th and enlarged ed.). Baltimore: Williams & Witkins.
  • R. D. Savage (April 1974). "Wechsler's Measurement and Appraisal of Adult Intelligence, 5th ed". British Journal of Industrial Medicine (Review). 31 (2): 169. PMC 1009574.
• Wechsler, David (1939). The Measurement of Adult Intelligence. Baltimore (MD): Williams & Witkins.
• Wechsler, David (1958). The Measurement and Appraisal of Adult Intelligence (4th ed.). Baltimore (MD): Williams & Witkins. Retrieved 4 June 2013.
• Weiss, Lawrence G.; Saklofske, Donald H.; Coalson, Diane; Raiford, Susan, eds. (2010). WAIS-IV Clinical Use and Interpretation: Scientist-Practitioner Perspectives. Practical Resources for the Mental Health Professional. Alan S. Kaufman (Foreword). Amsterdam: Academic Press. ISBN 978-0-12-375035-8.

• FAQ/Finding Information About Psychological Tests (American Psychological Association)
• Classics in the History of Psychology