Charles Spearman (1927) (figure 7) has proposed a theory of two factors (General Ability "g" and Special Ability), which is based on the observation that those people who perform well on the tests of general intelligence do usually perform well on tests for special abilities (like verbal or mathematical processing) and vice-versa. Thus, Spearman's main idea was that gifted people are gifted in general and dull people are generally dull the same way. This theory was widely accepted for practical use. The tests, directly measuring Spearman's "g" are in a wide practice nowadays. Raven Standard Progressive Matrices, developed by J.C. Raven and distributed by US Psychological Corporation is test battery of this kind.
There's a belief, that most fundamental principles in psychometrics and testing became available by 1930, and that with a few exceptions, the remainder of the 20th century was devoted to applying or refining these principles. The later theories divided into two groups with one tended to be based on Spearman's model, while the other followers divide intelligence into several components. Some notable theories are listed below.
- Thurstone (1938) believed that Spearman's hypothesis of a general factor did not fully reflect the intelligence and was a practical success only because of the simple averaging of more primary mental abilities. He identified 7 of them, which he considered would describe intelligence more specifically. The abilities are verbal relations, verbal fluency, number, memory, perceptual speed, induction, and spatial visualization. Though this theory is accepted, it is not widely used for practical assessment because of the greater difficulties with analysis and applications.
- Raymond Cattell (1963) believed that "g" is composed of fluid and crystallized intelligence. He considered that fluid intelligence was based on the abilities to see the relations between things and prevailed during the first part of a person's life, while the crystallized intelligence was based on acquired knowledge and skills and prevailed after about 40 years old. There a few tests according to this theory available, e.g. KAIT (Kaufman Adolescent and Adult Intelligence Test), which is a general intelligence tests, including two separate Crystallized and Fluid scales.
- Robert Sternberg (1973 — present) proposed a triarchic model of three intelligences, namely: analytical (A), practical (P) and creative (C). A is similar to standard psychometric definition of intelligence, P is the one, solving real life problems in everyday life and C is responsible for insight, synthesis, and the ability to react to novel stimuli and situations. The existence of P and C shows that this theory views intelligence wider then it gets from a classical Spearman's "g" theory and, in part, explains why some people, who have very high IQ often fail to succeed in life. Steinberg has developed STAT (Sternberg Triarchic Abilities Test), a battery of multiple-choice questions that measures all 3 intelligences on separate scales. This theory is notable for marking the shift of concepts towards understanding the nature of intelligence by identifying the underlying cognitive processing involved in intelligence.
- Howard Gardner (1983) developed a theory of multiple intelligences (7 originally). Unlike most other theories, Gardner does support his approach purely through statistical reanalysis of data, but also involves developmental, neurophysiologic, case study and educational evidence. According to Gardner, the intelligence consists of linguistic, logical-mathematic, spatial, musical, bodily-kinesthetic, intrapersonal, interpersonal. Later he has added existential and naturalist intelligences. There are some multiple intelligences quizzes and tests, but I am unaware about any solution with a properly proved reliability and validity.
- Vernon & Carroll (1960's — nowadays) proposed a hierarchical model, where Spearman's general intelligence "g" takes the top position, then it can be broken down into major group factors, which are also divided into minor group factors, close to Thurstone's primary mental abilities. This model is one of the most widely accepted nowadays and is in constant development with the cooperation of the authors.
Ivan Tugoy, 2003