The Wechsler Adult Intelligence Scale (WAIS) is an IQ test designed to measure intelligence and cognitive ability in adults and older adolescents. The original WAIS (Form I) was published in February 1955 by David Wechsler, as a revision of the Wechsler–Bellevue Intelligence Scale, released in 1939. It is currently in its fourth edition (WAIS-IV) released in 2008 by Pearson, and is the most widely used IQ test, for both adults and older adolescents, in the world. History 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." 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 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). 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. 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