David Wechsler

David Wechsler (January 12, 1896 - May 2, 1981) was a leading American psychologist. He developed well-known intelligence scales, such as the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler Intelligence Scale for Children (WISC).

Biography

Wechsler was born in a Jewish family in Lespezi, Romania, and immigrated with his parents to the United States as a child. He studied at the City College of New York and Columbia University, where he earned his master's degree in 1917 and his Ph.D. in 1925 under the direction of Robert S. Woodworth. During World War I he worked with the United States Army to develop psychological tests to screen new draftees while studying under Charles Spearman and Karl Pearson.

After short stints at various locations (including five years in private practice), Wechsler became chief psychologist at Bellevue Psychiatric Hospital in 1932, where he stayed until 1967. He died in 1981, his psychological tests already being highly respected.

Intelligence scales

Wechsler is best known for his intelligence tests. The Wechsler Adult Intelligence Scale (WAIS) was developed first in 1939 and then called the Wechsler-Bellevue Intelligence Test. From these he derived the Wechsler Intelligence Scale for Children (WISC) in 1949 and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) in 1967. Wechsler originally created these tests to find out more about his patients at the Bellevue clinic and he found the then-current Binet IQ test unsatisfactory. The tests are still based on his philosophy that intelligence is "the global capacity to act purposefully, to think rationally, and to deal effectively with [one's] environment" (cited in Kaplan & Saccuzzo, p. 256).

The Wechsler scales introduced many novel concepts and breakthroughs to the intelligence testing movement. First, he did away with the quotient scores of older intelligence tests (the Q in "I.Q."). Instead, he assigned an arbitrary value of 100 to the mean intelligence and added or subtracted another 15 points for each standard deviation above or below the mean the subject was. Rejecting a concept of global intelligence (as was propagated by Charles Spearman), he divided the concept of intelligence into two main areas: verbal and performance (non-verbal) areas, each further subdivided and tested with a different subtest. These conceptualizations are still reflected in the most recent versions of the Wechsler scales.

The WAIS is today the most commonly administered psychological test (Kaplan & Sacuzzo, 2005). The tests are currently updated approximately every ten years to compensate for the Flynn effect.

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). Weschler defined intelligence as "The global capacity of a person to act purposefully, to think rationally, and to deal effectively with his/her environment."

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).

The median full-scale IQ is centered at 100, 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. To qualify for entrance into Mensa a score of 130 is needed.

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, 7-16 yrs) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI, 2 1/2-7 yrs) 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. Digits forward: 123, Digits backward 321.)

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'

The Wechsler Intelligence Scale for Children (WISC), developed by David Wechsler, is an intelligence test for children between the ages of 6 and 16 inclusive that can be completed without reading or writing. The WISC generates an IQ score.

History

The WISC was originally developed as a downward extension of the Wechsler Adult Intelligence Scale in 1949. A revised edition (WISC-R) in 1974 as the WISC-R, and the third edition, the WISC-III in 1991. The current version, the WISC-IV, was produced in 2003. Each successive version has renormed the test to compensate for the Flynn effect, refined questions to make them less biased against minorities and females, and updated materials to make them more useful in the administration of the test.

Uses

The WISC is used not only as an intelligence test, but as a clinical tool. Many practitioners use it to diagnose attention-deficit hyperactivity disorder (ADHD) and learning disabilities, for example. This is usually done through a process called pattern analysis, in which the various subtests' scores are compared to one another (ipsative scoring) and clusters of unusually low scores in relation to the others are searched for. David Wechsler himself suggested this in 1958 (Kaplan & Saccuzzo, 2005).

However, the research does not show this to be a very effective way to diagnosis ADHD or learning disabilities (Watkins, Kush, & Glutting, 1997). The vast majority of ADHD children do not display certain subscores substantially below others, and many children who display such patterns do not have ADHD. Other patterns for children with learning disabilities show a similar lack of usefulness of the WISC as a diagnostic tool (Ward, Ward, Hatt, Young, & Moller, 1995).

When diagnosing children, best practice suggests that a multi-test battery should be used as learning problems, attention, and emotional difficulties can have similar symptoms, co-occur, or influence each other. For example, children with learning difficulties can become emotionally distraught and thus have concentration difficulties, begin to exhibit behavior problems, or both. Children with ADD or ADHD may show learning difficulties because of their attentional problems or also have learning disorder or mental retardation (or have nothing else). In short, while diagnosis of any childhood or adult difficulty should never be made based on IQ alone (or interview, physician examination, parent report, other test etc. for that matter) the cognitive ability test can help rule out, in conjunction with other tests and sources of information, other explanations for problems, uncover co-morbid problems, and be a rich source of information when properly analyzed and care is taken to avoid relying simply on the single summary IQ score (Sattler, ?year).

The empirical consensus is that the WISC is best used as a tool to evaluate intelligence and not to diagnose ADHD or learning disabled children. However, many clinicians use it to compare a child's cognitive development to his or her actual school or social performance. Using this discrepancy and other sources of data, the WISC can contribute information concerning a child's psychological well-being.

Translations

WISC has been translated or adapted to many languages, and norms have been established for a number of countries, including Spanish, Norwegian, Swedish, French (France and Canada), English (United States, Canada, United Kingdom), Chinese (Hong Kong), Greek , and Italian. Separate norms are established with each translation. (Norway uses the Swedish norms).

References

ISBN links support NWE through referral fees

• Kaplan, R.M. & Saccuzzo, D.P. (2005). Psychological Testing: Principles, applications, and issues. Belmont, CA: Thomson Wadsworth.
• Watkins, M.W., Kush, J., & Glutting, J.J. (1997). Discriminant and predictive validity of the WISC-III ACID profile among children with learning disabilities. Psychology in the Schools, 34(4), 309-319.
• Ward, S.B., Ward, T. J., Hatt, C.V., Young, D.L, & Mollner, N.R. (1995). The incidence and utility of the ACID, ACIDS, and SCAD profiles in a referred population. Psychology in the Schools, 32(4), 267-276.

External links

• WISC at Fairleigh Dickinson University site
• WISC-IV on Harcourt Assessment site
• Overview
• Official page
• More descriptions about individual tests
• PMID 12801187 - "Scoring reliability on the Wechsler Adult Intelligence Scale-Third Edition"
• PMID 10877468 - "Prorating Wechsler Adult Intelligence Scale-III summary scores"

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