Aug 31 / Iakovos Koukas

G Factor of Psychometrics

There are many types of IQ tests, which include a variety of content. There are verballinguistic tests, numerical-mathematical tests, spatial-visual tests, logical-abstract tests, mixed tests, and culture fair tests.

Charles Spearman, in 1904 made the first factor analysis of correlations between the tests. Spearman observed that children's performance ratings across unrelated school subjects were positively correlated. He suggested that these correlations were the result of an underlying general mental ability that influenced all kinds of mental tests. Spearman proposed that an individual's mental performance is the result of a single general ability factor, which he labeled g and many narrow special ability factors. Spearman also developed the two-factor theory of intelligence, which includes the concept of g factor or general intelligence factor, but also the s factor of specific intellectual abilities (verbal, spatial, numerical, and mechanical).

The g factor (or general intelligence or general intelligence factor) is a psychometric construct that governs all cognitive tasks and abilities. G factor is a variable that summarizes positive correlations among different cognitive tasks and mental tests. One's performance on one kind of cognitive task tends to be comparable to the same person's performance on other kinds of cognitive tasks. IQ, g factor, general intelligence, general cognitive ability, and simply intelligence are terms used interchangeably to refer to what cognitive tests try to measure.

Modern models of intelligence, like John Carroll's three-stratum theory, represent cognitive abilities as a three-level hierarchy, where there are many narrow taskspecific special factors at the bottom of the hierarchy, some broad factors at the intermediate level, which are fluid intelligence (Gf), crystallized intelligence (Gc), general memory and learning (Gy), broad visual perception (Gv), broad auditory perception (Gu), broad retrieval ability (Gr), broad cognitive speediness (Gs), and processing speed (Gt), and at the top a single factor, the g factor, which is the variable common to all cognitive tasks.

Research has established that g is highly heritable. G is also a significant predictor of individual differences in education, status, income, and employment.