The diagnostic application of psychometrics was a forte of Wechsler. He began his career at a time (the late 1910s) when "Clinical Psychology" was virtually unknown to wider society. By the time he retired as head of the Bellevue Psychiatric Hospital (and member of the New York University College of Medicine in 1961), clinical psychology was a major area of the discipline (indeed, an integral part of everyday life). Wechslers' introduction to the assessment of cognitive abilities was serendipitous.

By chance, he was assigned to assist E.G. Boring in testing army recruits during World War I. His observations on the inadequacies of the Army Alpha Tests (designed to measure abilities of conscripts from wildly differing backgrounds) led him to realize that academically defined "intelligence" was conceptually impoverished, in no way applicable to "real life" situations. Wechsler's military service took him to London where he studied under Spearman and Pearson. These experiences led Wechsler to appreciate the diagnostic potential of ability measures. In 1934 he began construction of the most wildly used adult intelligence test battery ­ the Wechsler Adult Intelligence Scale (WAIS). Although the WAIS reigns supreme as Wechsler's memorial, he later developed many other scales for use with specialized groups. As an adjunct to the WAIS, Wechsler made another major contribution to psychology -- the 'Deviation Quotient'. Today, this commonly serves as an indication of adult individual differences in intelligence level. However, in our opinion, the rigidity involved in standardizing the WAIS, has made it slow to adapt to changes in the conceptualization of intelligence (particularly those that stem from multi-faceted cognitive ability theories [see Pallier, Roberts, & Stankov, 1999]).