Wechsler Adult Intelligence Scale

The Wechsler Adult Intelligence Scale is an IQ test designed to measure intelligence and cognitive ability in adults and older adolescents. For children between the ages of 6 and 16, Wechsler Intelligence Scale for Children is commonly used.
The original WAIS was published in February 1955 by David Wechsler, Chief Psychologist at Bellevue Hospital in New York City, as a revision of the Wechsler–Bellevue Intelligence Scale released in 1939. It is currently in its fifth edition, released in 2024 by Pearson. It is the most widely used IQ test, for both adults and older adolescents, in the world.

History

The WAIS was founded to get to know Wechsler's patients at Bellevue Hospital and on his 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." 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.
This theory differed greatly from the Binet-Simon Intelligence Test 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.

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.
Wechsler did not agree with the idea of a single score that the Binet test gave.
Wechsler argued that the Binet scale items were not valid for adult test-takers because the items were chosen specifically for use with children.
The "Binet scale's emphasis on speed, with timed tasks scattered throughout the scale, tended to unduly handicap older adults."
Wechsler believed that "mental age norms clearly did not apply to adults."
Wechsler criticized the then existing Binet scale because "it did not consider that intellectual performance could deteriorate as a person grew older."

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, many of the original concepts Wechsler argued for have become standards in psychological testing, including the point-scale concept and the performance-scale concept.

Wechsler–Bellevue Intelligence Scale

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

gathered tasks created for nonclinical purposes for administration as a "clinical test battery",
used the point scale concept instead of the age scale, and
included a non-verbal performance scale.
Point scale concept

In the Binet scales items were grouped according to age level. Each of these age levels was composed of a group of tasks that could be passed by two-thirds to three-quarters of the individuals in that level. This meant that items were not arranged according to content. Additionally, an individual taking a Binet test would only receive credit if a certain number of the tasks were completed. This meant that falling short just one task required for the credit, resulted in no credit at all.
The point scale concept significantly changed the way testing was done by assigning credits or points to each item. This had two large effects. First, this allowed items to be grouped according to content. Second, participants were able to receive a set number of points or credits for each item passed. The result was a test that could be made up of different content areas with both an overall score and a score for each content area. In turn, this allowed for an analysis to be made of an individual's ability in a variety of content areas.

The Non-Verbal Performance Scale

The non-verbal performance scale was also a critical difference from the Binet scale. The earlier Binet scale had been persistently and consistently criticized for its emphasis on language and verbal skills. Wechsler designed an entire scale that allowed the measurement of non-verbal intelligence. This became known as a performance scale. This scale required a subject to actively do something, such as copying symbols or pointing to a missing detail in a picture, rather than just answering questions. This was an important development, as it attempted to overcome biases that were caused by "language, culture, and education." Further, this scale also provided an opportunity to observe a different type of behavior, because something physical was required. Clinicians were able to observe how a participant reacted to the "longer interval of sustained effort, concentration, and attention" that the performance tasks required.
As the Wechsler–Bellevue scale was the first to effectively use the performance scale, it also introduced the "possibility of directly comparing an individual's verbal and nonverbal intelligence". This was possible as "the results of both scales were expressed in comparable units". The Binet scale did have performance tasks, but they were geared toward younger children. The Wechsler-Bellevue was also unique in that there were entire tests that were considered supplements or alternatives, including "performance" measures such as the Leiter International Performance Scale.

WAIS

The WAIS was initially created as a revision of the Wechsler–Bellevue Intelligence Scale, 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 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.

WAIS-R

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

WAIS-III

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.

WAIS-IV

The previous 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 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. There are several notable features in this version of the intelligence scale that make it unique from previous versions. Some of these changes include the removal of Picture Arrangement, Object Assembly, Mazes, Verbal IQ, and Performance IQ and the addition of five subtests that emphasize fluid reasoning and/or working memory.

Index scores and scales

There are four index scores representing major components of intelligence:

Verbal Comprehension Index
Perceptual Reasoning Index
Working Memory Index
Processing Speed Index

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

Full Scale IQ, based on the total combined performance of the VCI, PRI, WMI, and PSI. The WAIS-IV can generate an FSIQ in the range of 40 to 160.
General Ability Index, based only on the six subtests that the VCI and PRI comprise; it is intended to portray a snapshot of general intelligence that is less influenced by working memory and processing speed demands.

Index	Subtest	Core?	Description	Proposed abilities measured
Verbal Comprehension	Similarities		Describe how two words or concepts are similar.	Abstract verbal reasoning; semantic knowledge
Verbal Comprehension	Vocabulary		Name objects in pictures or define words presented to them.	Semantic knowledge; verbal comprehension and expression
Verbal Comprehension	Information		General knowledge questions	Degree of general information acquired from culture
Verbal Comprehension	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
Perceptual Reasoning	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
Perceptual 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
Perceptual Reasoning	Picture Completion		Select the missing part of a picture	Ability to quickly perceive visual details
Perceptual Reasoning	Figure Weights		View a stimulus book that pictures shapes on a scale 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
Working Memory	Arithmetic		Orally administered arithmetic word problems. Timed.	Quantitative reasoning, concentration, mental manipulation
Working Memory	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
Processing Speed	Coding		Transcribe a digit-symbol code using a key. The task is time-limited.	Processing speed, associative memory, graphomotor speed
Processing Speed	Cancellation		Scan arrangements of shapes and mark specific target shapes within a limited amount of time	Processing speed