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What is General Mental Ability g


The idea of general mental ability, or intelligence, was first conceptualised by Spearman in 1904. He reflected on the popularly held notion that some people are more academically able than others, noting that people who tend to perform well in one intellectual domain (e.g. science) also tend to perform well in other domains (e.g. languages, mathematics, etc.). He concluded that an underlying factor which he termed general intelligence, or ‘g’, accounted for this tendency for people to perform well across a wide range of areas, while differences in a person’s specific abilities or aptitudes accounted for their tendency to perform marginally better in one area than in another (e.g. to be marginally better at French than they are at Geography).

In his 1904 paper Spearman outlined the theoretical framework underpinning Classical Test Theory and factor analysis; the latter being the statistical procedure that is used to identify the shared factor (‘g’) that accounts for a person’s tendency to perform well (or badly) across a range of different academic tasks. Subsequent developments in the mathematics underpinning factor analysis, combined with advances in computing, meant that after the Second World War psychologists were able to begin exploring the structure of human mental abilities using these new statistical procedures.

Being most famous for his work on personality, and in particular the development of the 16PF*, the work that Raymond B. Cattell (1967) did on the structure of human intelligence has often been overlooked. Through an extensive research programme, Cattell and his colleagues identified that ‘g’ (general intelligence) could be decomposed into two highly correlated subtypes of mental ability, which he termed fluid and crystallised intelligence. Fluid intelligence is reasoning ability in its most abstract and purest form. It is the ability to analyse novel problems, identify the patterns and relationships that underpin these problems and extrapolate from these using logic. This ability is central to all logical problem solving and is crucial for solving scientific, technical and mathematical problems. Research has suggested that fluid intelligence is relatively independent of a person’s educational experience, and is strongly determined by genetic factors. As such, many psychologists consider fluid intelligence to be the ‘purest’ form of intelligence, or ‘innate mental ability. As such abstract reasoning tests are considered by many to be the best way to assess fluid intelligence. These tests are sometimes (wrongly) described as culture fair tests, as no specific knowledge is required (e.g. an extensive vocabulary, an understanding of numbers, etc.) to complete them.


Crystallised intelligence, on the other hand, consists of fluid intelligence as it is evidenced in culturally valued activities. High levels of crystallised intelligence are evidenced in a person’s good level of general knowledge, their extensive vocabulary and their ability to reason using words and numbers. In short, crystallised intelligence is the product of a person’s cultural and educational experience in interaction with their fluid intelligence. As such, traditional tests of verbal and numerical reasoning ability are considered by many to be the best measures of crystallised intelligence.





* 16PF is a Trademark of IPAT



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