working memory. The Verbal Comprehension Index (VCI) included the following tests: Information Similarities Vocabulary The Working Memory Index (WMI) included: Arithmetic Digit Span Letter-Number-Sequencing Subtest(s) not included in the sub-indices: Comprehension Supplementary subtest(s) (Only to be used for total VIQ index scoring and specified sub-index): Letter-Number-Sequencing Performance IQ (PIQ) Included six tests and it also provided two sub-indices; perceptual organization and processing speed. The Perceptual Organization Index (POI) included: Block Design Matrix Reasoning Picture Completion The Processing Speed Index (PSI) included: Digit Symbol-Coding Symbol Search Subtest(s) not included in the sub-indices: Picture Arrangement Supplementary subtests (Only to be used for total PIQ index scoring and specified sub-index): Object Assembly Symbol Search WAIS-IV The current version of the test, the WAIS-IV, which was released in 2008, is composed of 10 core subtests and five supplemental subtests, with the 10 core subtests yielding scaled scores that sum to derive the Full Scale IQ. With the WAIS-IV, the verbal/performance IQ scores from previous versions were removed and replaced by the index scores. The General Ability Index (GAI) was included, which consists of the Similarities, Vocabulary and Information subtests from the Verbal Comprehension Index and the Block Design, Matrix Reasoning and Visual Puzzles subtests from the Perceptual Reasoning Index. The GAI is clinically useful because it can be used as a measure of cognitive abilities that are less vulnerable to impairments of processing speed and working memory. Index scores and scales There are four index scores representing major components of intelligence: Verbal Comprehension Index (VCI) Perceptual Reasoning Index (PRI) Working Memory Index (WMI) Processing Speed Index (PSI) Two broad scores, which can be used to summarize general intellectual ability, can also be derived: Full Scale IQ (FSIQ), based on the total combined performance of the VCI, PRI, WMI, and PSI General Ability Index (GAI), based only on the six subtests that the VCI and PRI comprise. Standardization The WAIS-IV was standardized on a sample of 2,200 people in the United States, ranging in age from 16 to 90. The demographic characteristics of the sample were modeled after the proportions of different groups in an analysis of data from the U.S. Census Bureau. An extension of the standardization has been conducted with 688 Canadians in the same age range. Age range and uses The WAIS-IV measure is acceptable for use with people who are 16–90 years of age. For people younger than 16, the Wechsler