Editing Intelligence quotient (section)

===General factor (''g'')===
{{main|g factor (psychometrics)|l1=''g'' factor}}
The many different kinds of IQ tests include a wide variety of item content. Some test items are visual, while many are verbal. Test items vary from being based on abstract-reasoning problems to concentrating on arithmetic, vocabulary, or general knowledge.

The British psychologist [[Charles Spearman]] in 1904 made the first formal [[factor analysis]] of [[correlation]]s between the tests. He observed that children's school grades across seemingly unrelated school subjects were positively correlated, and reasoned that these correlations reflected the influence of an underlying general mental ability that entered into performance on all kinds of mental tests. He suggested that all mental performance could be conceptualized in terms of a single general ability factor and a large number of narrow task-specific ability factors. Spearman named it ''g'' for "general factor" and labeled the specific factors or abilities for specific tasks ''s''.{{sfn|Deary|2001|pp=6–12}} In any collection of test items that make up an IQ test, the score that best measures ''g'' is the composite score that has the highest correlations with all the item scores. Typically, the "''g''-loaded" composite score of an IQ test battery appears to involve a common strength in abstract reasoning across the test's item content.{{Citation needed|date=June 2020}}