Cattell–Horn–Carroll theory

The Cattell–Horn–Carroll theory is an integration of two previously established theoretical models of intelligence: the theory of fluid and crystallized intelligence (Gf-Gc), and Carroll's three-stratum theory, a hierarchical, three-stratum model of intelligence. Due to substantial similarities between the two theories they were amalgamated to form the Cattell–Horn–Carroll theory. However, some researchers, including John Carroll, have questioned not only the need for, but also the empirical basis of, the theory.

In the late 1990s the CHC model was expanded by McGrew, later revised with the help of Flanagan. Later extensions of the model are detailed in McGrew and Schneider and McGrew. There are a fairly large number of distinct individual differences in cognitive ability, and CHC theory holds that the relationships among them can be derived by classifying them into three different strata: stratum I, "narrow" abilities; stratum II, "broad abilities"; and stratum III, consisting of a single "general ability" (or g).

Today, the Cattell–Horn–Carroll theory is widely accepted as the most comprehensive and empirically supported theory of cognitive abilities, informing a substantial body of research and the ongoing development of IQ (Intelligence Quotient) tests.

Background

Development of the CHC model

The Cattell–Horn–Carroll theory of intelligence is a synthesis of Cattell and Horn's Gf-Gc model of fluid and crystallised intelligence and Carroll's Three Stratum Hierarchy. Awareness of the similarities between Cattel and Horn's Gf-Gc expanded model abilities and Carroll's Broad Stratum II abilities were highlighted at a meeting in 1985 concerning the revision of the Woodcock-Johnson Psycho-Educational Battery. At this meeting Horn presented the Gf-Gc theory to several prominent figures in intelligence testing, including John B. Carroll. Carroll was already a vocal proponent of the Cattell-Horn theory, stating in 1993 that the Gf-Gc model "appears to offer the most well-founded and reasonable approach to an acceptable theory of the structure of cognitive abilities". This fortuitous meeting was the starting point for the integration of the two theories. The integration of the two theories evolved through a series of bridging events that occurred over two decades. Although there are many similarities between the two models, Horn consistently and unyieldingly argued against a single general ability g factor. Charles Spearman first proposed the existence of the g-factor (also known as general intelligence) in the early 20th century after discovering significant positive correlations between children's scores in seemingly unrelated academic subjects. Unlike Horn, Carroll argued that evidence for a single 'general' ability was overwhelming, and insisted that g was essential to a theory of human intelligence.

Cattell and Horn's Gf–Gc Model

Raymond B. Cattell (20 March 1905 – 2 February 1998) was the first to propose a distinction between "fluid intelligence" (Gf) and "crystallised intelligence" (Gc). Charles Spearman's s factors are considered a prequel to this idea, along with Thurstone's theory of Primary Mental Abilities. By 1991, John Horn, a student of Cattell's, had expanded the Gf-Gc model to include 9 or 10 broad abilities.

Fluid intelligence refers to quantitative reasoning, processing ability, adaptability to new environments and novel problem solving. Crystallised intelligence (Gc) refers to the accumulation of knowledge (general, procedural and declarative). Gc tasks include problem solving with familiar materials and culture-fair tests of general knowledge and vocabulary. Gf and Gc are both factors of g (general intelligence). Though distinct, there is interaction, as fluid intelligence is a determining factor in the speed with which crystallised knowledge is accumulated. Crystallised intelligence is known to increase with age as we accumulate knowledge throughout the lifespan. Fluid processing ability reaches a peak around age 20, then declines steadily. Recent research has explored the idea that training on working memory tasks can transfer to improvements in fluid intelligence. This idea did not hold under further scrutiny.

Carroll's three-stratum hierarchy

The American psychologist John B. Carroll (June 5, 1916 – July 1, 2003) made substantial contributions to psychology, psychometrics and educational linguistics. In 1993, Carroll published Human Cognitive Abilities: A Survey of Factor-Analytic Studies, in which he presented 'A Theory of Cognitive Abilities: The Three-Stratum Theory'. Carroll had re-analysed data-sets from 461 classic factor analytic studies of human cognition, distilling the results into 800 pages, thus providing a solid foundation for future research in human intelligence.

Carroll's three-stratum theory presented three levels of cognition: narrow abilities (stratum I), broad abilities (stratum II) and general abilities (stratum III).