g factor (psychometrics)

The g factor is a construct developed in <a href="/facts/Psychometric/56X26MDI">psychometric</a> investigations of <a href="/facts/Cognitive_skill/8L95q3bX">cognitive abilities</a> and human <a href="/facts/Intelligence/pRmAeRsw">intelligence</a>. It is a variable that summarizes positive <a href="/facts/Correlation/egkluAEm">correlations</a> among different cognitive tasks, reflecting the assertion that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks. The g factor typically accounts for 40 to 50 percent of the between-individual performance differences on a given <a href="/facts/Cognitive_test/07ruSL1L">cognitive test</a>, and composite scores ("IQ scores") based on many tests are frequently regarded as estimates of individuals' standing on the g factor. The terms <a href="/facts/Intelligence_quotient/rozfcXsk">IQ</a>, general intelligence, general cognitive ability, general mental ability, and simply intelligence are often used interchangeably to refer to this common core shared by cognitive tests. However, the g factor itself is a mathematical construct indicating the level of observed correlation between cognitive tasks. The measured value of this construct depends on the cognitive tasks that are used, and little is known about the underlying causes of the observed correlations.
The existence of the g factor was originally proposed by the English psychologist <a href="/facts/Charles_Spearman/3KzcgynP">Charles Spearman</a> in the early years of the 20th century. He observed that children's performance ratings, across seemingly unrelated school subjects, were positively <a href="/facts/Correlated/egkluAEm">correlated</a>, and reasoned that these correlations reflected the influence of an underlying general mental ability that entered into performance on all kinds of mental tests. Spearman suggested that all mental performance could be conceptualized in terms of a single general ability factor, which he labeled g, and many narrow task-specific ability factors. Soon after Spearman proposed the existence of g, it was challenged by <a href="/facts/Godfrey_Thomson/lzpPEUwU">Godfrey Thomson</a>, who presented evidence that such intercorrelations among test results could arise even if no g-factor existed. Today's factor models of intelligence typically represent cognitive abilities as a three-level hierarchy, where there are many narrow <a href="/facts/Factor_analysis/LT6B9I7D">factors</a> at the bottom of the hierarchy, a handful of broad, more general factors at the intermediate level, and at the apex a single factor, referred to as the g factor, which represents the variance common to all cognitive tasks.
Traditionally, research on g has concentrated on psychometric investigations of test data, with a special emphasis on <a href="/facts/Factor_analysis/LT6B9I7D">factor analytic</a> approaches. However, empirical research on the nature of g has also drawn upon experimental <a href="/facts/Cognitive_psychology/GnzIgx2I">cognitive psychology</a> and <a href="/facts/Mental_chronometry/K1SBWJ81">mental chronometry</a>, brain anatomy and physiology, <a href="/facts/Quantitative_genetics/r9ReNW6P">quantitative</a> and <a href="/facts/Molecular_genetics/Q8wsm0FE">molecular genetics</a>, and <a href="/facts/Evolution_of_human_intelligence/HcDgaT4B">primate evolution</a>. Research in the field of <a href="/facts/Behavioral_genetics/w7nscvfu">behavioral genetics</a> has shown that the construct of g is highly <a href="/facts/Heritability_of_IQ/3PAa75ra">heritable</a> in measured populations. It has a number of other biological correlates, including <a href="/facts/Brain_size/K0xy5XT5">brain size</a>. It is also a significant predictor of individual differences in many social outcomes, particularly in education and employment.
Critics have contended that an emphasis on g is misplaced and entails a devaluation of other important abilities. Some scientists, including <a href="/facts/Stephen_Jay_Gould/FtAcabjg">Stephen J. Gould</a>, have argued that the concept of g is a merely <a href="/facts/Reification_(fallacy)/g8kLcmaM">reified</a> construct rather than a <a href="/facts/Construct_validity/exjLSRJI">valid</a> measure of human intelligence.

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g factor (psychometrics)