Wechsler-Bellevue Intelligence Scale: Foundation of modern IQ testing

About the Wechsler-Bellevue Intelligence Scale

By the late 1930s, David Wechsler at the Bellevue Psychiatric Hospital in New York saw two problems with the Stanford-Binet that dominated American intelligence testing. First, the mental-age formula (IQ = MA / CA × 100) broke down in adulthood - a 30-year-old with a mental age of 35 should logically have an IQ of 117, but in practice adult cognitive abilities stop growing around 16-20 and any further 'mental age' increase was an artifact of test difficulty rather than real growth. Second, single-score IQ obscured important profile information - a person could have very strong verbal abilities and very weak performance abilities, but the Stanford-Binet collapsed these into one number.

Wechsler's solution had two parts. First, replace mental-age IQ with deviation IQ: compare the subject's score to the distribution of scores in their own age group, with the mean fixed at 100 and SD at 15. This is the convention every modern IQ test now uses. Second, report separate Verbal IQ and Performance IQ scores in addition to a Full Scale IQ - giving clinicians a profile rather than a single number.

The Wechsler-Bellevue had 11 subtests (6 Verbal + 5 Performance) including direct descendants of Kohs Block Design (1923), the Healy Pictorial Completion (1914), Knox Cube (1914), and various Army Alpha/Beta items. Wechsler revised it in 1955 as the WAIS, and subsequent revisions (WAIS-R 1981, WAIS-III 1997, WAIS-IV 2008) have carried his framework forward. The current WAIS-IV is the most-used adult intelligence test in the world; it gets about 2-3 million annual administrations in clinical practice.

The 3 subtests

Source

All test materials and historical content on this page are transcribed from:

The Wechsler-Bellevue itself remains under Pearson copyright (the modern WAIS is its descendant). We describe the scale's structure and significance; the actual items are not in the public domain. This page is a documentation reference, not an interactive test. Read it on Internet Archive: https://archive.org/details/measurementofadu00wech.