Editing Human intelligence (section)

== Measuring ==
{{Main|Intelligence quotient}}
{{further|Psychometrics}}
[[Image:Terman1916Fig2IQDistribution.png|thumb|alt=Chart of IQ Distributions on 1916 Stanford-Binet Test|Score distribution chart for sample of 905 children tested on 1916 Stanford-Binet Test]]

The approach to understanding intelligence with the most supporters and published research over the longest period of time is based on [[Psychometrics|psychometric]] testing. It is also by far the most widely used in practical settings.<ref name=APA1995/> [[Intelligence quotient]] (IQ) tests include the [[Stanford-Binet]], [[Raven's Progressive Matrices]], the [[Wechsler Adult Intelligence Scale]] and the [[Kaufman Assessment Battery for Children]]. There are also psychometric tests that are not intended to measure intelligence itself but some closely related construct such as scholastic aptitude. In the United States examples include the [[Secondary School Admission Test|SSAT]], the [[SAT]], the [[ACT (test)|ACT]], the [[Graduate Record Examinations|GRE]], the [[MCAT]], the [[LSAT]], and the [[GMAT]].<ref name=APA1995/> Regardless of the method used, almost any test that requires examinees to reason and has a wide range of question difficulty will produce intelligence scores that are approximately [[normal distribution|normally distributed]] in the general population.<ref>Jensen, A. R. (1998). ''The g factor: The science of mental ability.'' Westport, CT: Praeger.</ref><ref>{{cite journal | last1 = Warne | first1 = R. T. | last2 = Godwin | first2 = L. R. | last3 = Smith | first3 = K. V. | year = 2013 | title = Are there more gifted people than would be expected in a normal distribution? An investigation of the overabundance hypothesis | journal = Journal of Advanced Academics | volume = 24 | issue = 4| pages = 224–241 | doi = 10.1177/1932202x13507969 | s2cid = 145575694 }}</ref>

Intelligence tests are widely used in educational,<ref>{{cite journal | last1 = Ritter | first1 = N. | last2 = Kilinc | first2 = E. | last3 = Navruz | first3 = B. | last4 = Bae | first4 = Y. | year = 2011 | title = Test Review: Test of Nonverbal Intelligence-4 (TONI-4) | journal = Journal of Psychoeducational Assessment | volume = 29 | issue = 5| pages = 384–388 | doi = 10.1177/0734282911400400 | s2cid = 146910420 }}</ref> business, and military settings because of their efficacy in predicting behavior. IQ and ''g'' (discussed in the next section) are correlated with many important social outcomes—individuals with low IQs are more likely to be divorced, have a child out of marriage, be incarcerated, and need long-term welfare support, while individuals with high IQs are associated with more years of education, higher status jobs and higher income.<ref name="isbn1591471818">{{Cite book |author=Geary, David M. |title=The Origin of the Mind: Evolution of Brain, Cognition, and General Intelligence |publisher=American Psychological Association (APA) |year=2004 |isbn=978-1-59147-181-3 |oclc=217494183}}</ref> Intelligence as measured by Psychometric tests has been found to be highly correlated with successful training and performance outcomes (e.g., adaptive performance),<ref>{{cite journal |last1=Bertua |first1=Cristina |last2=Anderson |first2=Neil |last3=Salgado |first3=Jesús F. |title=The predictive validity of cognitive ability tests: A UK meta-analysis |journal=Journal of Occupational and Organizational Psychology |date=September 2005 |volume=78 |issue=3 |pages=387–409 |doi=10.1348/096317905X26994}}</ref><ref>{{cite journal |last1=Lang |first1=Jonas W. B. |last2=Kersting |first2=Martin |last3=Hülsheger |first3=Ute R. |last4=Lang |first4=Jessica |title=General mental ability, narrower cognitive abilities, and job performance: The perspective of the nested factors model of cognitive abilities |journal=Personnel Psychology |date=5 August 2010 |volume=63 |issue=3 |pages=595–640 |doi=10.1111/j.1744-6570.2010.01182.x|url=https://cris.maastrichtuniversity.nl/ws/files/74901322/Hulsheger_2010_General_mental_ability_narrower_cognitive.pdf }}</ref><ref>{{cite journal |last1=Stasielowicz |first1=Lukasz |title=How important is cognitive ability when adapting to changes? A meta-analysis of the performance adaptation literature |journal=Personality and Individual Differences |date=November 2020 |volume=166 |pages=110178 |doi=10.1016/j.paid.2020.110178|s2cid=225033285 |url=http://psyarxiv.com/qu4t2/ }}</ref> and IQ/''g'' is the single best predictor of successful job performance; however, some researchers although largely concurring with this finding have advised caution in citing the strength of the claim due to a number of factors, these include: statistical assumptions imposed underlying some of these studies, studies done prior to 1970 which appear inconsistent with more recent studies, and ongoing debates within the Psychology literature as to the validity of current IQ measurement tools.<ref name=RichardsonNorgate2015>{{Cite journal | author= Richardson, K. | author2= Norgate, S. | year=2015 | title = Does IQ Really Predict Job Performance? | journal = Applied Developmental Science | volume=19 | issue=3 | pages=153–169| doi= 10.1080/10888691.2014.983635| pmid= 26405429 | pmc= 4557354 }}</ref><ref name=Ree1992>{{Cite journal |author=Ree, M.J. |author2=Earles, J.A. |year=1992 |title=Intelligence Is the Best Predictor of Job Performance |journal=Current Directions in Psychological Science |volume=1 |issue=3 |pages=86–89 |doi=10.1111/1467-8721.ep10768746|s2cid=145352062 }}</ref>

=== General intelligence factor or ''g'' ===
{{Main|g factor (psychometrics)}}

There are many different kinds of IQ tests using a wide variety of test tasks. Some tests consist of a single type of task, others rely on a broad collection of tasks with different contents (visual-spatial,<ref>{{cite journal | last1 = Delen | first1 = E. | last2 = Kaya | first2 = F. | last3 = Ritter | first3 = N. | year = 2012 | title = Test review: Test of Comprehensive Nonverbal Intelligence-2 (CTONI-2) | journal = Journal of Psychoeducational Assessment | volume = 30 | issue = 2| pages = 209–213 | doi = 10.1177/0734282911415614 | s2cid = 144773295 }}</ref> verbal, numerical) and asking for different cognitive processes (e.g., reasoning, memory, rapid decisions, visual comparisons, spatial imagery, reading, and retrieval of [[general knowledge]]). The psychologist [[Charles Spearman]] early in the 20th century carried out the first formal [[factor analysis]] of [[correlation]]s between various test tasks. He found a trend for all such tests to correlate positively with each other, which is called a ''positive manifold''. Spearman found that a single common factor explained the positive correlations among tests. Spearman named it ''g'' for "[[general intelligence factor]]". He interpreted it as the core of human intelligence that, to a larger or smaller degree, influences success in all cognitive tasks and thereby creates the positive manifold. This interpretation of ''g'' as a common cause of test performance is still dominant in psychometrics. (Although, an alternative interpretation was recently advanced by van der Maas and colleagues.<ref>{{cite journal|last=van der Maas|first=H. L. J.|author2=Dolan, C. V. |author3=Grasman, R. P. P. P. |author4=Wicherts, J. M. |author5=Huizenga, H. M. |author6= Raijmakers, M. E. J. |s2cid=10152374|title=A dynamical model of general intelligence: The positive manifold of intelligence by mutualism|journal=Psychological Review|year=2006|volume=113|pages=842–861|doi=10.1037/0033-295X.113.4.842|pmid=17014305|issue=4}}</ref> Their ''mutualism model'' assumes that intelligence depends on several independent mechanisms, none of which influences performance on all cognitive tests. These mechanisms support each other so that efficient operation of one of them makes efficient operation of the others more likely, thereby creating the positive manifold.)

IQ tests can be ranked by how highly they load on the ''g'' factor. Tests with high ''g''-loadings are those that correlate highly with most other tests. One comprehensive study investigating the correlations between a large collection of tests and tasks<ref>{{cite journal|last=Marshalek|first=B. |author2=Lohman, D. F. |author3=Snow, R. E. |title=The complexity continuum in the radex and hierarchical models of intelligence|journal=Intelligence|year=1983|volume=7|pages=107–127|doi=10.1016/0160-2896(83)90023-5|issue=2}}</ref> has found that the [[Raven's Progressive Matrices]] have a particularly high correlation with most other tests and tasks. The ''Raven's'' is a test of inductive reasoning with abstract visual material. It consists of a series of problems, sorted approximately by increasing difficulty. Each problem presents a 3 x 3 matrix of abstract designs with one empty cell; the matrix is constructed according to a rule, and the person must find out the rule to determine which of 8 alternatives fits into the empty cell. Because of its high correlation with other tests, the Raven's Progressive Matrices are generally acknowledged as a good indicator of general intelligence. This is problematic, however, because there are substantial gender differences on the ''Raven's'',<ref>{{cite journal|last=Lynnn|first=R.|author2=Irving, P.|title=Sex differences on the progressive matrices: A meta-analysis|journal=Intelligence|year=2004|volume=32|pages=481–498|doi=10.1016/j.intell.2004.06.008|issue=5}}</ref> which are not found when ''g'' is measured directly by computing the general factor from a broad collection of tests.<ref>{{cite journal|last=Halpern|first=D. F.|author2=LaMay, M. L.|title=The smarter sex: A critical review of sex differences in intelligence|journal=[[Educational Psychology Review]]|year=2000|volume=12|pages=229–246|doi=10.1023/A:1009027516424|issue=2|s2cid=142961814}}</ref>

Several critics, such as [[Stephen Jay Gould]], have been critical of ''g'', seeing it as a statistical artifact, and that IQ tests instead measure a number of unrelated abilities.<ref name="mom">''The Mismeasure of Man'', Stephen Jay Gould, Norton, 1996</ref><ref name="Schlinger2003">{{Cite journal |author=Schlinger, H.D. |year=2003 |title=The Myth of Intelligence |url=https://www.questia.com/PM.qst?a=o&se=gglsc&d=5001903843 |journal=The Psychological Record |volume=53 |issue=1 |pages=15–33 |access-date=2008-03-18 |archive-date=2009-10-07 |archive-url=http://arquivo.pt/wayback/20091007164436/http://www.questia.com/PM.qst?a=o&se=gglsc&d=5001903843 |url-status=dead }}</ref> The 1995 American Psychological Association's report "[[Intelligence: Knowns and Unknowns]]" stated that IQ tests do correlate and that the view that ''g'' is a statistical artifact was a minority one.

=== General collective intelligence factor or ''c'' ===
{{Main|Collective intelligence}}

A recent scientific understanding of collective intelligence, defined as a group's general ability to perform a wide range of tasks,<ref>{{Cite journal|last1=Woolley|first1=Anita Williams|last2=Chabris|first2=Christopher F.|last3=Pentland|first3=Alex|last4=Hashmi|first4=Nada|last5=Malone|first5=Thomas W.|s2cid=74579|date=2010-10-29|title=Evidence for a Collective Intelligence Factor in the Performance of Human Groups|journal=Science|volume=330|issue=6004|pages=686–688|doi=10.1126/science.1193147|issn=0036-8075|pmid=20929725|bibcode=2010Sci...330..686W|doi-access=free}}</ref> expands the areas of human intelligence research applying similar methods and concepts to groups. Definition, operationalization and methods are similar to the psychometric approach of general individual intelligence where an individual's performance on a given set of cognitive tasks is used to measure intelligence indicated by the [[G factor (psychometrics)|general intelligence factor ''g'']] extracted via factor analysis.<ref>{{Cite journal|last=Spearman, C.E.|date=1904|title="General intelligence," objectively determined and measured|journal=American Journal of Psychology |volume=15 |issue= 2|pages= 201–293|doi=10.2307/1412107|jstor=1412107}}</ref> In the same vein, collective intelligence research aims to discover a ''c'' factor' explaining between-group differences in performance as well as structural and group compositional causes for it.<ref>{{Cite journal|last1=Woolley|first1=Anita Williams|last2=Aggarwal|first2=Ishani|last3=Malone|first3=Thomas W.|date=2015-12-01|title=Collective Intelligence and Group Performance|journal=Current Directions in Psychological Science|volume=24|issue=6|pages=420–424|doi=10.1177/0963721415599543|s2cid=146673541|issn=0963-7214}}</ref>

=== Historical psychometric theories ===
{{Main|Intelligence quotient#History}}

Several different theories of intelligence have historically been important for [[psychometrics]]. Often they emphasized more factors than a single one like in ''[[g factor (psychometrics)|g factor]]''.

=== Cattell–Horn–Carroll theory ===
{{Main|Cattell–Horn–Carroll theory}}

Many of the broad, recent IQ tests have been greatly influenced by the [[Cattell–Horn–Carroll theory]]. It is argued to reflect much of what is known about intelligence from research. A hierarchy of factors for human intelligence is used. ''g'' is at the top. Under it there are 10 broad abilities that in turn are subdivided into 70 narrow abilities. The broad abilities are:<ref name=Kaufman2009>IQ Testing 101, Alan S. Kaufman, 2009, Springer Publishing Company, {{ISBN|978-0-8261-0629-2}}</ref>
*Fluid intelligence (Gf): includes the broad ability to reason, form concepts, and solve problems using unfamiliar information or novel procedures.
*Crystallized intelligence (Gc): includes the breadth and depth of a person's acquired knowledge, the ability to communicate one's knowledge, and the ability to reason using previously learned experiences or procedures.
*Quantitative reasoning (Gq): the ability to comprehend quantitative concepts and relationships and to manipulate numerical symbols.
*Reading & writing ability (Grw): includes basic reading and writing skills.
*Short-term memory (Gsm): is the ability to apprehend and hold information in immediate awareness and then use it within a few seconds.
*Long-term storage and retrieval (Glr): is the ability to store information and fluently retrieve it later in the process of thinking.
*Visual processing (Gv): is the ability to perceive, analyze, synthesize, and think with visual patterns, including the ability to store and recall visual representations.
*Auditory processing (Ga): is the ability to analyze, synthesize, and discriminate auditory stimuli, including the ability to process and discriminate speech sounds that may be presented under distorted conditions.
*Processing speed (Gs): is the ability to perform automatic cognitive tasks, particularly when measured under pressure to maintain focused attention.
*Decision/reaction time/speed (Gt): reflect the immediacy with which an individual can react to stimuli or a task (typically measured in seconds or fractions of seconds; not to be confused with Gs, which typically is measured in intervals of 2–3 minutes). See [[Mental chronometry]].
Modern tests do not necessarily measure of all of these broad abilities. For example, Gq and Grw may be seen as measures of school achievement and not IQ.<ref name=Kaufman2009/> Gt 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/>

=== Insufficiency of measurement via IQ ===
{{Excerpt|Intelligence quotient|Validity as a measure of intelligence}}
A study suggested that intelligence is composed of distinct cognitive systems, each of which having its own capacity and being (to some degree) independent of other components, with the cognitive profile being emergent from [[neuroanatomy|anatomically]] distinct cognitive systems (such as brain regions or neural networks).<ref>{{cite news |title=IQ scores not accurate marker of intelligence, study shows |url=https://www.cbsnews.com/news/iq-scores-not-accurate-marker-of-intelligence-study-shows/ |access-date=7 November 2022 |work=CBS News}}</ref><ref>{{cite journal |last1=Hampshire |first1=Adam |last2=Highfield |first2=Roger R. |last3=Parkin |first3=Beth L. |last4=Owen |first4=Adrian M. |title=Fractionating Human Intelligence |journal=Neuron |date=20 December 2012 |volume=76 |issue=6 |pages=1225–1237 |doi=10.1016/j.neuron.2012.06.022 |pmid=23259956 |s2cid=1536350 |language=en |issn=0896-6273|doi-access=free }}</ref> For example, IQ and reading-/language-related traits/[[skill]]s appear to be [[Genetic correlation|influenced]] "at least partly [by] distinct genetic factors".<ref>{{cite news |title=Massive genome study informs the biology of reading and language |url=https://medicalxpress.com/news/2022-08-massive-genome-biology-language.html |access-date=18 September 2022 |work=[[Max Planck Society]] via medicalxpress.com |language=en}}</ref><ref>{{cite journal |last1=Eising |first1=Else |last2=Mirza-Schreiber |first2=Nazanin |last3=de Zeeuw |first3=Eveline L. |last4=Wang |first4=Carol A. |last5=Truong |first5=Dongnhu T. |last6=Allegrini |first6=Andrea G. |last7=Shapland |first7=Chin Yang |last8=Zhu |first8=Gu |last9=Wigg |first9=Karen G. |last10=Gerritse |first10=Margot L. |display-authors=et al. |title=Genome-wide analyses of individual differences in quantitatively assessed reading- and language-related skills in up to 34,000 people |journal=Proceedings of the National Academy of Sciences |date=30 August 2022 |volume=119 |issue=35 |pages=e2202764119 |doi=10.1073/pnas.2202764119 |pmid=35998220 |pmc=9436320 |bibcode=2022PNAS..11902764E |language=en |issn=0027-8424|doi-access=free}}</ref>

Various types of potential measures related to some definitions of intelligence but not part of IQ measurement include:
* [[Cognitive flexibility]] – abilities in switching between different concepts, or to adapt behaviour in novel or changing environments<ref>{{cite web |last1=Sahakian |first1=Barbara Jacquelyn |last2=Langley |first2=Christelle |last3=Leong |first3=Victoria |title=IQ tests can't measure it, but 'cognitive flexibility' is key to learning and creativity |url=https://theconversation.com/iq-tests-cant-measure-it-but-cognitive-flexibility-is-key-to-learning-and-creativity-163284 |website=The Conversation |date=23 June 2021 |access-date=7 November 2022 |language=en}}</ref>
* [[Moral intelligence]]<ref name="Gardner">{{cite web |last1=Gardner |first1=Howard |title=Who Owns Intelligence? |url=http://arowe.pbworks.com/w/file/fetch/51366150/Who%20Owns%20Intelligence.pdf |access-date=7 November 2022}}</ref><ref>{{cite book |last1=Bartlett |first1=Steven James |title=Epistemological Intelligence |date=2017 |url=https://philarchive.org/archive/BAREI-4 |access-date=7 November 2022}}</ref>
* [[Prioritization]] and goal-selection
* Direct measures of brain activity<ref name="Gardner"/> and other [[neuroimaging intelligence testing]] – partly investigated in the [[Neuroscience and intelligence|neuroscience of intelligence]]