Editing Intelligence quotient (section)

===Cattell–Horn–Carroll theory===
{{main|Cattell–Horn–Carroll theory}}
[[File:Raymond Cattell.jpg|thumb|upright|right|Psychologist [[Raymond Cattell]] defined [[fluid and crystallized intelligence]] and authored the [[Cattell Culture Fair III]] IQ test.]]
[[Raymond Cattell]] (1941) proposed two types of cognitive abilities in a revision of Spearman's concept of general intelligence. [[Fluid intelligence]] (Gf) was hypothesized as the ability to solve novel problems by using reasoning, and [[crystallized intelligence]] (Gc) was hypothesized as a knowledge-based ability that was very dependent on education and experience. In addition, fluid intelligence was hypothesized to decline with age, while crystallized intelligence was largely resistant to the effects of aging. The theory was almost forgotten, but was revived by his student [[John L. Horn]] (1966) who later argued Gf and Gc were only two among several factors, and who eventually identified nine or ten broad abilities. The theory continued to be called Gf-Gc theory.<ref name=Kaufman2009/>

[[John Bissell Carroll|John B. Carroll]] (1993), after a comprehensive reanalysis of earlier data, proposed the [[three stratum theory]], which is a hierarchical model with three levels. The bottom stratum consists of narrow abilities that are highly specialized (e.g., induction, spelling ability). The second stratum consists of broad abilities. Carroll identified eight second-stratum abilities. Carroll accepted Spearman's concept of general intelligence, for the most part, as a representation of the uppermost, third stratum.<ref name=Lubinski2004>{{cite journal |last1=Lubinski |first1=David |title=Introduction to the Special Section on Cognitive Abilities: 100 Years After Spearman's (1904) "'General Intelligence,' Objectively Determined and Measured" |journal=Journal of Personality and Social Psychology |date=2004 |volume=86 |issue=1 |pages=96–111 |doi=10.1037/0022-3514.86.1.96 |pmid=14717630 |s2cid=6024297}}</ref>{{sfn|Carroll|1993|p={{page needed|date=October 2020}}}}

In 1999, a merging of the Gf-Gc theory of Cattell and Horn with Carroll's Three-Stratum theory has led to the Cattell–Horn–Carroll theory (CHC Theory), with ''g'' as the top of the hierarchy, ten broad abilities below, and further subdivided into seventy narrow abilities on the third stratum. CHC Theory has greatly influenced many of the current broad IQ tests.<ref name=Kaufman2009/>

Modern tests do not necessarily measure all of these broad abilities. For example, ''quantitative knowledge'' and ''reading and writing ability'' may be seen as measures of school achievement and not IQ.<ref name=Kaufman2009/> ''Decision speed'' may be difficult to measure without special equipment. ''g'' was earlier often subdivided into only Gf and Gc, which were thought to correspond to the nonverbal or performance subtests and verbal subtests in earlier versions of the popular Wechsler IQ test. More recent research has shown the situation to be more complex.<ref name="Kaufman2009" /> Modern comprehensive IQ tests do not stop at reporting a single IQ score. Although they still give an overall score, they now also give scores for many of these more restricted abilities, identifying particular strengths and weaknesses of an individual.<ref name="Kaufman2009" />