Wechsler Adult Intelligence Scale – IV (WAIS-IV)

The author of the original WAIS defined ‘intelligence’ as; “The global capacity of a person to act purposefully, to think rationally, and to deal effectively with his/her environment.” (David Wechsler, 1939. The measurement of adult intelligence. Baltimore: Williams & Wilkins, p. 229.)

The current version of the Wechsler Adult Intelligence Scale – (WAIS-IV) was released in 2008.  It can be administered to people between the ages of 16 and 90.  It is composed of 10 core subtests and five supplemental subtests.  There are five aspects of intelligence that are identified:

• Full Scale IQ (FSIQ) is considered the most valid measure of overall cognitive ability.
• Verbal Comprehension Index (VCI) is designed to measure verbal reasoning and concept formation.
• Perceptual Reasoning Index (PRI) is designed to measure fluid reasoning in the perceptual domain with tasks that assess nonverbal concept formation, visual perception and organization, visual-motor coordination, learning, and the ability to separate figure and ground in visual stimuli.
• Working Memory Index (WMI) is the ability to sustain attention, concentrate, and exert mental control.
• Processing Speed Index (PSI) is the ability to process simple or routine visual material without making errors.

These five indexes were constructed to have means of 100 and standard deviations of 15 IQ points.  An IQ of 100 defines the performance of the average adult at that age.  About two-thirds of all adults obtain IQs between 85 and 115 (1 standard deviation below and above the mean).  About 95 percent score between 70 and 130 (2 standard deviations on either side of the mean).  More than 99 percent obtain scores between 55 and 145 (3 standard deviations from the mean).

The following are commonly used diagnostic labels together with corresponding numerical limits in terms of IQs and percentages.