d two subscales: verbal (information, vocabulary, comprehension, arithmetic, similarities, and digit span) and performance (picture completion and arrangement, block design, object assembly, and digit symbol). The next most popular test, the Stanford-Binet, employs fifteen subtests with four subscales: verbal reasoning (e.g. "How are a porpoise, dolphin and whale different from a shark?", abstract/visual reasoning (completion of matrix problems), quantitative reasoning (e.g. sequential questions such as, "What comes next: 5 10 9 18 17 34 33 __ __"), and short-term memory (repeating digits forwards and backwards). Raven's Matrices relies entirely on nonverbal methods to measure IQ, by requiring the test subject to discern the relationships between different objects. While both the Wechsler and Stanford-Binet are administered to individuals, Raven's Matrices may be given to a large number of people at the same time. Interestingly, despite the vast differences between the two tests, correlations between Raven's and Wechsler scores in the general population fall between 0.40 and 0.75 (Burke, 1958, 1985; Court & Raven, 1995; as cited in Mackintosh, 1998).Theories of IntelligenceFactor analysis has been employed to find patterns in the correlation matrices of IQ tests, with varying results (Mackintosh, 1998). In 1927, Charles Spearman developed a two-factor theory of intelligence, which involves the idea that there is a general intelligence (g) that may be measured with varying degrees of accuracy by tests. He proposed that the reason why all tests of ability correlate to a certain extent is because they all measure g. Other theories began to arise: by 1941, Thurstone & Thurstone suggested that IQ tests must measure a number of independent factors, which they called "primary mental abilities," and that researchers ought to focus on creating factorially pure tests. They found six distinct primary mental abilities: numerical, verbal comprehensi...
