Wechsler Adult Intelligence Scale (WAIS)

Wechsler Adult Intelligence scale (WAIS) is an IQ test that is the primary instrument used to measure adult and adolescent intelligence from ages 16 to 90. First published in 1955 by David Wechsler, the most recent edition (WAIS-IV) was released in 2008 (Kaufman & Lichtenberger, 2006). Its purpose it also to measure nonintellectual features such as understanding of social norms, rapidity of perception, and comprehension, as well as abstract reasoning, memory, attention retention, and imagination.

The Wechsler Scale defines intelligence as "the global capacity of a person to act purposefully, to think rationally, and to deal effectively with his environment" (Kaufman & Lichtenberger, 2006, p.7) and includes non-verbal items (i.e. performance items) as well as verbal items in attempt to define intelligence.

The WAIS was initially created as revision of the Wechsler-Bellevue Intelligence Scale (WBIS), that was composed of subtests extracted from other intelligence tests popular at the time such as the Simon-Binet test. The latest edition, the WAIS-IV (2008), consists of 10 core subtests - that are the full-scale IQ test - and five additional subtests.

The WAIS has been consistently tested and has a reputation for reliability and validity. The test-retest reliability, for instance, of WAIS-III peaked at .96 (for Full Scale and Verbal IQ) with a low of .89 for processing Sped and Working Memory and the Standard Error of Measurement is generally small. Experts, using comparisons and tests, have also established the construct validity, face validity, criterion validity and content validity of the WAIS, with some tests having more construct validity than others (Ryan & Schnakenberg-Ott, 2003).

The WAIS-IV was standardized on 2,200 individuals in the United States ranging from 16 to 90 years old. The test was applied, too, to 688 Canadians in the same age range (ibid.). The entire test -- paper -- and pencil- takes between 60 to 90 minutes for the core tests to be completed (Hess, 2001; Rogers, 2001)

The median of the Full-Scale IQ is centered at 100, with a standard deviation of 15. Generally, 68% of adults fall between one standard deviation above and below the mean (i.e. between 85 and 115) on a normal bell-shaped distribution.

An abbreviated four-subtest version of the WAIS-III (called the Wechsler Abbreviated Scale of Intelligence (WASI)) has been released enabling clinicians to perform a validated verbal, performance and full-scale IQ in approximately 30 minutes.