David Wechsler - Intelligence Scales

Intelligence Scales

Wechsler is best known for his intelligence tests. He is one of the most influential advocates of the role of nonintellective factors in testing. He emphasized that factors other than intellectual ability are involved in intelligent behavior. Wechsler objected to the single score offered by the 1937 Binet scale. Although his test did not directly measure nonintellective factors, it took these factors into careful account in its underlying theory. 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 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. While not rejecting the concept of global intelligence (as conceptualized by his teacher Charles Spearman), he divided the concept of intelligence into two main areas: verbal and performance (non-verbal) scales, each evaluated with different subtests.

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.