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.