g factor (psychometrics) - Wikipedia

The g factor (also known as general intelligence, general mental ability or general intelligence factor) is a construct developed in psychometric ... gfactor(psychometrics) FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Psychometricfactoralsoknownas"generalintelligence" "Generalintelligence"redirectshere.NottobeconfusedwithIntelligence,Artificialgeneralintelligence,orIntelligencequotient. Thegfactor(alsoknownasgeneralintelligence,generalmentalabilityorgeneralintelligencefactor)isaconstructdevelopedinpsychometricinvestigationsofcognitiveabilitiesandhumanintelligence.Itisavariablethatsummarizespositivecorrelationsamongdifferentcognitivetasks,reflectingthefactthatanindividual'sperformanceononetypeofcognitivetasktendstobecomparabletothatperson'sperformanceonotherkindsofcognitivetasks.Thegfactortypicallyaccountsfor40to50percentofthebetween-individualperformancedifferencesonagivencognitivetest,andcompositescores("IQscores")basedonmanytestsarefrequentlyregardedasestimatesofindividuals'standingonthegfactor.[1]ThetermsIQ,generalintelligence,generalcognitiveability,generalmentalability,andsimplyintelligenceareoftenusedinterchangeablytorefertothiscommoncoresharedbycognitivetests.[2]However,thegfactoritselfismerelyamathematicalconstructindicatingthelevelofobservedcorrelationbetweencognitivetasks.[3]Themeasuredvalueofthisconstructdependsonthecognitivetasksthatareused,andlittleisknownabouttheunderlyingcausesoftheobservedcorrelations. TheexistenceofthegfactorwasoriginallyproposedbytheEnglishpsychologistCharlesSpearmanintheearlyyearsofthe20thcentury.Heobservedthatchildren'sperformanceratings,acrossseeminglyunrelatedschoolsubjects,werepositivelycorrelated,andreasonedthatthesecorrelationsreflectedtheinfluenceofanunderlyinggeneralmentalabilitythatenteredintoperformanceonallkindsofmentaltests.Spearmansuggestedthatallmentalperformancecouldbeconceptualizedintermsofasinglegeneralabilityfactor,whichhelabeledg,andmanynarrowtask-specificabilityfactors.SoonafterSpearmanproposedtheexistenceofg,itwaschallengedbyGodfreyThomson,whopresentedevidencethatsuchintercorrelationsamongtestresultscouldariseevenifnog-factorexisted.[4]Today'sfactormodelsofintelligencetypicallyrepresentcognitiveabilitiesasathree-levelhierarchy,wheretherearemanynarrowfactorsatthebottomofthehierarchy,ahandfulofbroad,moregeneralfactorsattheintermediatelevel,andattheapexasinglefactor,referredtoasthegfactor,whichrepresentsthevariancecommontoallcognitivetasks. Traditionally,researchonghasconcentratedonpsychometricinvestigationsoftestdata,withaspecialemphasisonfactoranalyticapproaches.However,empiricalresearchonthenatureofghasalsodrawnuponexperimentalcognitivepsychologyandmentalchronometry,brainanatomyandphysiology,quantitativeandmoleculargenetics,andprimateevolution.[5]Somescientistsconsidergasastatisticalregularityanduncontroversial,andageneralcognitivefactorappearsindatacollectedfrompeopleinnearlyeveryhumanculture.[6]Yet,thereisnoconsensusastowhatcausesthepositivecorrelationsbetweentests. Researchinthefieldofbehavioralgeneticshasshownthattheconstructofgishighlyheritableinmeasuredpopulations.Ithasanumberofotherbiologicalcorrelates,includingbrainsize.Itisalsoasignificantpredictorofindividualdifferencesinmanysocialoutcomes,particularlyineducationandemployment.Themostwidelyacceptedcontemporarytheoriesofintelligenceincorporatethegfactor.[7]However,criticsofghavecontendedthatanemphasisongismisplacedandentailsadevaluationofotherimportantabilities.StephenJ.Gouldfamouslydenouncedtheconceptofgassupportinganunrealisticreifiedviewofhumanintelligence. Contents 1Cognitiveabilitytesting 2Theories 2.1Mentalenergyorefficiency 2.2Samplingtheory 2.3Mutualism 3Factorstructureofcognitiveabilities 4"Indifferenceoftheindicator" 5Populationdistribution 6Spearman'slawofdiminishingreturns 7Practicalvalidity 7.1Academicachievement 7.2Jobattainment 7.3Jobperformance 7.4Income 7.5Othercorrelates 8Geneticandenvironmentaldeterminants 9Neuroscientificfindings 10ginnon-humans 11g(orc)inhumangroups 12Otherbiologicalassociations 13Groupsimilaritiesanddifferences 14Relationtootherpsychologicalconstructs 14.1Elementarycognitivetasks 14.2Workingmemory 14.3Piagetiantasks 14.4Personality 14.5Creativity 15Challenges 15.1Gf-Gctheory 15.2Theoriesofuncorrelatedabilities 15.3Flynn'smodel 15.4TheMismeasureofMan 15.4.1CritiqueofGould[citationneeded] 15.5Othercritiquesofg 16Seealso 17References 18Bibliography Cognitiveabilitytesting[edit] Spearman'scorrelationmatrixforsixmeasuresofschoolperformance.Allthecorrelationsarepositive,thepositivemanifoldphenomenon.Thebottomrowshowsthegloadingsofeachperformancemeasure.[8] Classics French English Math Pitch Music Classics – French .83 – English .78 .67 – Math .70 .67 .64 – Pitchdiscrimination .66 .65 .54 .45 – Music .63 .57 .51 .51 .40 – g .958 .882 .803 .750 .673 .646 SubtestintercorrelationsinasampleofScottishsubjectswhocompletedtheWAIS-Rbattery.ThesubtestsareVocabulary,Similarities,Information,Comprehension,Picturearrangement,Blockdesign,Arithmetic,Picturecompletion,Digitspan,Objectassembly,andDigitsymbol.Thebottomrowshowsthegloadingsofeachsubtest. [9] V S I C PA BD A PC DSp OA DS V – S .67 - I .72 .59 - C .70 .58 .59 - PA .51 .53 .50 .42 - BD .45 .46 .45 .39 .43 - A .48 .43 .55 .45 .41 .44 – PC .49 .52 .52 .46 .48 .45 .30 - DSp .46 .40 .36 .36 .31 .32 .47 .23 - OA .32 .40 .32 .29 .36 .58 .33 .41 .14 - DS .32 .33 .26 .30 .28 .36 .28 .26 .27 .25 - g .83 .80 .80 .75 .70 .70 .68 .68 .56 .56 .48 Correlationsbetweenmentaltests Cognitiveabilitytestsaredesignedtomeasuredifferentaspectsofcognition.Specificdomainsassessedbytestsincludemathematicalskill,verbalfluency,spatialvisualization,andmemory,amongothers.However,individualswhoexcelatonetypeoftesttendtoexcelatotherkindsoftests,too,whilethosewhodopoorlyononetesttendtodosoonalltests,regardlessofthetests'contents.[10]TheEnglishpsychologistCharlesSpearmanwasthefirsttodescribethisphenomenon.[11]Inafamousresearchpaperpublishedin1904,[12]heobservedthatchildren'sperformancemeasuresacrossseeminglyunrelatedschoolsubjectswerepositivelycorrelated.Thisfindinghassincebeenreplicatednumeroustimes.Theconsistentfindingofuniversallypositivecorrelationmatricesofmentaltestresults(orthe"positivemanifold"),despitelargedifferencesintests'contents,hasbeendescribedas"arguablythemostreplicatedresultinallpsychology".[13]Zeroornegativecorrelationsbetweentestssuggestthepresenceofsamplingerrororrestrictionoftherangeofabilityinthesamplestudied.[14] Usingfactoranalysisorrelatedstatisticalmethods,itispossibletocomputeasinglecommonfactorthatcanberegardedasasummaryvariablecharacterizingthecorrelationsbetweenallthedifferenttestsinatestbattery.Spearmanreferredtothiscommonfactorasthegeneralfactor,orsimplyg.(Byconvention,gisalwaysprintedasalowercaseitalic.)Mathematically,thegfactorisasourceofvarianceamongindividuals,whichentailsthatonecannotmeaningfullyspeakofanyoneindividual'smentalabilitiesconsistingofgorotherfactorstoanyspecifieddegrees.Onecanonlyspeakofanindividual'sstandingong(orotherfactors)comparedtootherindividualsinarelevantpopulation.[14][15][16] Differenttestsinatestbatterymaycorrelatewith(or"loadonto")thegfactorofthebatterytodifferentdegrees.Thesecorrelationsareknownasgloadings.Anindividualtesttaker'sgfactorscore,representingtheirrelativestandingonthegfactorinthetotalgroupofindividuals,canbeestimatedusingthegloadings.Full-scaleIQscoresfromatestbatterywillusuallybehighlycorrelatedwithgfactorscores,andtheyareoftenregardedasestimatesofg.Forexample,thecorrelationsbetweengfactorscoresandfull-scaleIQscoresfromDavidWechsler'stestshavebeenfoundtobegreaterthan.95.[1][14][17]ThetermsIQ,generalintelligence,generalcognitiveability,generalmentalability,orsimplyintelligencearefrequentlyusedinterchangeablytorefertothecommoncoresharedbycognitivetests.[2] Thegloadingsofmentaltestsarealwayspositiveandusuallyrangebetween.10and.90,withameanofabout.60andastandarddeviationofabout.15.Raven'sProgressiveMatricesisamongthetestswiththehighestgloadings,around.80.Testsofvocabularyandgeneralinformationarealsotypicallyfoundtohavehighgloadings.[18][19]However,thegloadingofthesametestmayvarysomewhatdependingonthecompositionofthetestbattery.[20] Thecomplexityoftestsandthedemandstheyplaceonmentalmanipulationarerelatedtothetests'gloadings.Forexample,intheforwarddigitspantestthesubjectisaskedtorepeatasequenceofdigitsintheorderoftheirpresentationafterhearingthemonceatarateofonedigitpersecond.Thebackwarddigitspantestisotherwisethesameexceptthatthesubjectisaskedtorepeatthedigitsinthereverseordertothatinwhichtheywerepresented.Thebackwarddigitspantestismorecomplexthantheforwarddigitspantest,andithasasignificantlyhighergloading.Similarly,thegloadingsofarithmeticcomputation,spelling,andwordreadingtestsarelowerthanthoseofarithmeticproblemsolving,textcomposition,andreadingcomprehensiontests,respectively.[14][21] Testdifficultyandgloadingsaredistinctconceptsthatmayormaynotbeempiricallyrelatedinanyspecificsituation.Teststhathavethesamedifficultylevel,asindexedbytheproportionoftestitemsthatarefailedbytesttakers,mayexhibitawiderangeofgloadings.Forexample,testsofrotememoryhavebeenshowntohavethesamelevelofdifficultybutconsiderablylowergloadingsthanmanyteststhatinvolvereasoning.[21][22] Theories[edit] Whiletheexistenceofgasastatisticalregularityiswell-establishedanduncontroversialamongexperts,thereisnoconsensusastowhatcausesthepositiveintercorrelations.Severalexplanationshavebeenproposed.[23] Mentalenergyorefficiency[edit] CharlesSpearmanreasonedthatcorrelationsbetweentestsreflectedtheinfluenceofacommoncausalfactor,ageneralmentalabilitythatentersintoperformanceonallkindsofmentaltasks.However,hethoughtthatthebestindicatorsofgwerethoseteststhatreflectedwhathecalledtheeductionofrelationsandcorrelates,whichincludedabilitiessuchasdeduction,induction,problemsolving,graspingrelationships,inferringrules,andspottingdifferencesandsimilarities.Spearmanhypothesizedthatgwasequivalentwith"mentalenergy".However,thiswasmoreofametaphoricalexplanation,andheremainedagnosticaboutthephysicalbasisofthisenergy,expectingthatfutureresearchwoulduncovertheexactphysiologicalnatureofg.[24] FollowingSpearman,ArthurJensenmaintainedthatallmentaltaskstapintogtosomedegree.AccordingtoJensen,thegfactorrepresentsa"distillate"ofscoresondifferenttestsratherthanasummationoranaverageofsuchscores,withfactoranalysisactingasthedistillationprocedure.[19]Hearguedthatgcannotbedescribedintermsoftheitemcharacteristicsorinformationcontentoftests,pointingoutthatverydissimilarmentaltasksmayhavenearlyequalgloadings.Wechslersimilarlycontendedthatgisnotanabilityatallbutrathersomegeneralpropertyofthebrain.Jensenhypothesizedthatgcorrespondstoindividualdifferencesinthespeedorefficiencyoftheneuralprocessesassociatedwithmentalabilities.[25]Healsosuggestedthatgiventheassociationsbetweengandelementarycognitivetasks,itshouldbepossibletoconstructaratioscaletestofgthatusestimeastheunitofmeasurement.[26] Samplingtheory[edit] Theso-calledsamplingtheoryofg,originallydevelopedbyEdwardThorndikeandGodfreyThomson,proposesthattheexistenceofthepositivemanifoldcanbeexplainedwithoutreferencetoaunitaryunderlyingcapacity.Accordingtothistheory,thereareanumberofuncorrelatedmentalprocesses,andalltestsdrawupondifferentsamplesoftheseprocesses.Theintercorrelationsbetweentestsarecausedbyanoverlapbetweenprocessestappedbythetests.[27][28]Thus,thepositivemanifoldarisesduetoameasurementproblem,aninabilitytomeasuremorefine-grained,presumablyuncorrelatedmentalprocesses.[16] IthasbeenshownthatitisnotpossibletodistinguishstatisticallybetweenSpearman'smodelofgandthesamplingmodel;bothareequallyabletoaccountforintercorrelationsamongtests.[29]Thesamplingtheoryisalsoconsistentwiththeobservationthatmorecomplexmentaltaskshavehighergloadings,becausemorecomplextasksareexpectedtoinvolvealargersamplingofneuralelementsandthereforehavemoreofthemincommonwithothertasks.[30] Someresearchershavearguedthatthesamplingmodelinvalidatesgasapsychologicalconcept,becausethemodelsuggeststhatgfactorsderivedfromdifferenttestbatteriessimplyreflectthesharedelementsoftheparticulartestscontainedineachbatteryratherthanagthatiscommontoalltests.Similarly,highcorrelationsbetweendifferentbatteriescouldbeduetothemmeasuringthesamesetofabilitiesratherthanthesameability.[31] Criticshavearguedthatthesamplingtheoryisincongruentwithcertainempiricalfindings.Basedonthesamplingtheory,onemightexpectthatrelatedcognitivetestssharemanyelementsandthusbehighlycorrelated.However,somecloselyrelatedtests,suchasforwardandbackwarddigitspan,areonlymodestlycorrelated,whilesomeseeminglycompletelydissimilartests,suchasvocabularytestsandRaven'smatrices,areconsistentlyhighlycorrelated.Anotherproblematicfindingisthatbraindamagefrequentlyleadstospecificcognitiveimpairmentsratherthanageneralimpairmentonemightexpectbasedonthesamplingtheory.[16][32] Mutualism[edit] The"mutualism"modelofgproposesthatcognitiveprocessesareinitiallyuncorrelated,butthatthepositivemanifoldarisesduringindividualdevelopmentduetomutualbeneficialrelationsbetweencognitiveprocesses.Thusthereisnosingleprocessorcapacityunderlyingthepositivecorrelationsbetweentests.Duringthecourseofdevelopment,thetheoryholds,anyoneparticularlyefficientprocesswillbenefitotherprocesses,withtheresultthattheprocesseswillendupbeingcorrelatedwithoneanother.ThussimilarlyhighIQsindifferentpersonsmaystemfromquitedifferentinitialadvantagesthattheyhad.[16][33]Criticshavearguedthattheobservedcorrelationsbetweenthegloadingsandtheheritabilitycoefficientsofsubtestsareproblematicforthemutualismtheory.[34] Factorstructureofcognitiveabilities[edit] AnillustrationofSpearman'stwo-factorintelligencetheory.Eachsmallovalisahypotheticalmentaltest.Theblueareascorrespondtotest-specificvariance(s),whilethepurpleareasrepresentthevarianceattributedtog. Factoranalysisisafamilyofmathematicaltechniquesthatcanbeusedtorepresentcorrelationsbetweenintelligencetestsintermsofasmallernumberofvariablesknownasfactors.Thepurposeistosimplifythecorrelationmatrixbyusinghypotheticalunderlyingfactorstoexplainthepatternsinit.Whenallcorrelationsinamatrixarepositive,astheyareinthecaseofIQ,factoranalysiswillyieldageneralfactorcommontoalltests.ThegeneralfactorofIQtestsisreferredtoasthegfactor,andittypicallyaccountsfor40to50percentofthevarianceinIQtestbatteries.[35]Thepresenceofcorrelationsbetweenmanywidelyvaryingcognitivetestshasoftenbeentakenasevidencefortheexistenceofg,butMcFarland(2012)showedthatsuchcorrelationsdonotprovideanymoreorlesssupportfortheexistenceofgthanfortheexistenceofmultiplefactorsofintelligence.[36] CharlesSpearmandevelopedfactoranalysisinordertostudycorrelationsbetweentests.Initially,hedevelopedamodelofintelligenceinwhichvariationsinallintelligencetestscoresareexplainedbyonlytwokindsofvariables:first,factorsthatarespecifictoeachtest(denoteds);andsecond,agfactorthataccountsforthepositivecorrelationsacrosstests.ThisisknownasSpearman'stwo-factortheory.LaterresearchbasedonmorediversetestbatteriesthanthoseusedbySpearmandemonstratedthatgalonecouldnotaccountforallcorrelationsbetweentests.Specifically,itwasfoundthatevenaftercontrollingforg,sometestswerestillcorrelatedwitheachother.Thisledtothepostulationofgroupfactorsthatrepresentvariancethatgroupsoftestswithsimilartaskdemands(e.g.,verbal,spatial,ornumerical)haveincommoninadditiontothesharedgvariance.[37] AnillustrationofJohnB.Carroll'sthreestratumtheory,aninfluentialcontemporarymodelofcognitiveabilities.Thebroadabilitiesrecognizedbythemodelarefluidintelligence(Gf),crystallizedintelligence(Gc),generalmemoryandlearning(Gy),broadvisualperception(Gv),broadauditoryperception(Gu),broadretrievalability(Gr),broadcognitivespeediness(Gs),andprocessingspeed(Gt).Carrollregardedthebroadabilitiesasdifferent"flavors"ofg. Throughfactorrotation,itis,inprinciple,possibletoproduceaninfinitenumberofdifferentfactorsolutionsthataremathematicallyequivalentintheirabilitytoaccountfortheintercorrelationsamongcognitivetests.Theseincludesolutionsthatdonotcontainagfactor.Thusfactoranalysisalonecannotestablishwhattheunderlyingstructureofintelligenceis.Inchoosingbetweendifferentfactorsolutions,researchershavetoexaminetheresultsoffactoranalysistogetherwithotherinformationaboutthestructureofcognitiveabilities.[38] Therearemanypsychologicallyrelevantreasonsforpreferringfactorsolutionsthatcontainagfactor.Theseincludetheexistenceofthepositivemanifold,thefactthatcertainkindsoftests(generallythemorecomplexones)haveconsistentlylargergloadings,thesubstantialinvarianceofgfactorsacrossdifferenttestbatteries,theimpossibilityofconstructingtestbatteriesthatdonotyieldagfactor,andthewidespreadpracticalvalidityofgasapredictorofindividualoutcomes.Thegfactor,togetherwithgroupfactors,bestrepresentstheempiricallyestablishedfactthat,onaverage,overallabilitydifferencesbetweenindividualsaregreaterthandifferencesamongabilitieswithinindividuals,whileafactorsolutionwithorthogonalfactorswithoutgobscuresthisfact.Moreover,gappearstobethemostheritablecomponentofintelligence.[39]Researchutilizingthetechniquesofconfirmatoryfactoranalysishasalsoprovidedsupportfortheexistenceofg.[38] Agfactorcanbecomputedfromacorrelationmatrixoftestresultsusingseveraldifferentmethods.Theseincludeexploratoryfactoranalysis,principalcomponentsanalysis(PCA),andconfirmatoryfactoranalysis.Differentfactor-extractionmethodsproducehighlyconsistentresults,althoughPCAhassometimesbeenfoundtoproduceinflatedestimatesoftheinfluenceofgontestscores.[20][40] Thereisabroadcontemporaryconsensusthatcognitivevariancebetweenpeoplecanbeconceptualizedatthreehierarchicallevels,distinguishedbytheirdegreeofgenerality.Atthelowest,leastgeneralleveltherearemanynarrowfirst-orderfactors;atahigherlevel,therearearelativelysmallnumber–somewherebetweenfiveandten–ofbroad(i.e.,moregeneral)second-orderfactors(orgroupfactors);andattheapex,thereisasinglethird-orderfactor,g,thegeneralfactorcommontoalltests.[41][42][43]ThegfactorusuallyaccountsforthemajorityofthetotalcommonfactorvarianceofIQtestbatteries.[44]ContemporaryhierarchicalmodelsofintelligenceincludethethreestratumtheoryandtheCattell–Horn–Carrolltheory.[45] "Indifferenceoftheindicator"[edit] Spearmanproposedtheprincipleoftheindifferenceoftheindicator,accordingtowhichtheprecisecontentofintelligencetestsisunimportantforthepurposesofidentifyingg,becausegentersintoperformanceonallkindsoftests.Anytestcanthereforebeusedasanindicatorofg.[6]FollowingSpearman,ArthurJensenmorerecentlyarguedthatagfactorextractedfromonetestbatterywillalwaysbethesame,withinthelimitsofmeasurementerror,asthatextractedfromanotherbattery,providedthatthebatteriesarelargeanddiverse.[46]Accordingtothisview,everymentaltest,nomatterhowdistinctive,callsongtosomeextent.Thusacompositescoreofanumberofdifferenttestswillloadontogmorestronglythananyoftheindividualtestscores,becausethegcomponentscumulateintothecompositescore,whiletheuncorrelatednon-gcomponentswillcanceleachotherout.Theoretically,thecompositescoreofaninfinitelylarge,diversetestbatterywould,then,beaperfectmeasureofg.[47] Incontrast,L.L.Thurstonearguedthatagfactorextractedfromatestbatteryreflectstheaverageofalltheabilitiescalledforbytheparticularbattery,andthatgthereforevariesfromonebatterytoanotherand"hasnofundamentalpsychologicalsignificance."[48]Alongsimilarlines,JohnHornarguedthatgfactorsaremeaninglessbecausetheyarenotinvariantacrosstestbatteries,maintainingthatcorrelationsbetweendifferentabilitymeasuresarisebecauseitisdifficulttodefineahumanactionthatdependsonjustoneability.[49][50] Toshowthatdifferentbatteriesreflectthesameg,onemustadministerseveraltestbatteriestothesameindividuals,extractgfactorsfromeachbattery,andshowthatthefactorsarehighlycorrelated.Thiscanbedonewithinaconfirmatoryfactoranalysisframework.[23]WendyJohnsonandcolleagueshavepublishedtwosuchstudies.[51][52]Thefirstfoundthatthecorrelationsbetweengfactorsextractedfromthreedifferentbatterieswere.99,.99,and1.00,supportingthehypothesisthatgfactorsfromdifferentbatteriesarethesameandthattheidentificationofgisnotdependentonthespecificabilitiesassessed.Thesecondstudyfoundthatgfactorsderivedfromfouroffivetestbatteriescorrelatedatbetween.95–1.00,whilethecorrelationsrangedfrom.79to.96forthefifthbattery,theCattellCultureFairIntelligenceTest(theCFIT).TheyattributedthesomewhatlowercorrelationswiththeCFITbatterytoitslackofcontentdiversityforitcontainsonlymatrix-typeitems,andinterpretedthefindingsassupportingthecontentionthatgfactorsderivedfromdifferenttestbatteriesarethesameprovidedthatthebatteriesarediverseenough.Theresultssuggestthatthesamegcanbeconsistentlyidentifiedfromdifferenttestbatteries.[41][53] Populationdistribution[edit] Theformofthepopulationdistributionofgisunknown,becausegcannotbemeasuredonaratioscale[clarificationneeded].(ThedistributionsofscoresontypicalIQtestsareroughlynormal,butthisisachievedbyconstruction,i.e.,bynormalizingtherawscores.)Ithasbeenargued[who?]thatthereareneverthelessgoodreasonsforsupposingthatgisnormallydistributedinthegeneralpopulation,atleastwithinarangeof±2standarddeviationsfromthemean.Inparticular,gcanbethoughtofasacompositevariablethatreflectstheadditiveeffectsofmanyindependentgeneticandenvironmentalinfluences,andsuchavariableshould,accordingtothecentrallimittheorem,followanormaldistribution.[54] Spearman'slawofdiminishingreturns[edit] Anumberofresearchershavesuggestedthattheproportionofvariationaccountedforbygmaynotbeuniformacrossallsubgroupswithinapopulation.Spearman'slawofdiminishingreturns(SLODR),alsotermedthecognitiveabilitydifferentiationhypothesis,predictsthatthepositivecorrelationsamongdifferentcognitiveabilitiesareweakeramongmoreintelligentsubgroupsofindividuals.Morespecifically,(SLODR)predictsthatthegfactorwillaccountforasmallerproportionofindividualdifferencesincognitivetestsscoresathigherscoresonthegfactor. (SLODR)wasoriginallyproposedbyCharlesSpearman,[55]whoreportedthattheaveragecorrelationbetween12cognitiveabilitytestswas.466in78normalchildren,and.782in22"defective"children.DettermanandDanielrediscoveredthisphenomenonin1989.[56]TheyreportedthatforsubtestsofboththeWAISandtheWISC,subtestintercorrelationsdecreasedmonotonicallywithabilitygroup,rangingfromapproximatelyanaverageintercorrelationof.7amongindividualswithIQslessthan78to.4amongindividualswithIQsgreaterthan122.[57] (SLODR)hasbeenreplicatedinavarietyofchildandadultsampleswhohavebeenmeasuredusingbroadarraysofcognitivetests.Themostcommonapproachhasbeentodivideindividualsintomultipleabilitygroupsusinganobservableproxyfortheirgeneralintellectualability,andthentoeithercomparetheaverageinterrelationamongthesubtestsacrossthedifferentgroups,ortocomparetheproportionofvariationaccountedforbyasinglecommonfactor,inthedifferentgroups.[58]However,asbothDearyetal.(1996).[58]andTucker-Drob(2009)[59]havepointedout,dividingthecontinuousdistributionofintelligenceintoanarbitrarynumberofdiscreteabilitygroupsislessthanidealforexamining(SLODR).Tucker-Drob(2009)[59]extensivelyreviewedtheliteratureon(SLODR)andthevariousmethodsbywhichithadbeenpreviouslytested,andproposedthat(SLODR)couldbemostappropriatelycapturedbyfittingacommonfactormodelthatallowstherelationsbetweenthefactoranditsindicatorstobenonlinearinnature.HeappliedsuchafactormodeltoanationallyrepresentativedataofchildrenandadultsintheUnitedStatesandfoundconsistentevidencefor(SLODR).Forexample,Tucker-Drob(2009)foundthatageneralfactoraccountedforapproximately75%ofthevariationinsevendifferentcognitiveabilitiesamongverylowIQadults,butonlyaccountedforapproximately30%ofthevariationintheabilitiesamongveryhighIQadults. Arecentmeta-analyticstudybyBlumandHolling[60]alsoprovidedsupportforthedifferentiationhypothesis.Asopposedtomostresearchonthetopic,thisworkmadeitpossibletostudyabilityandagevariablesascontinuouspredictorsofthegsaturation,andnotjusttocomparelower-vs.higher-skilledoryoungervs.oldergroupsoftestees.Resultsdemonstratethatthemeancorrelationandgloadingsofcognitiveabilitytestsdecreasewithincreasingability,yetincreasewithrespondentage.(SLODR),asdescribedbyCharlesSpearman,couldbeconfirmedbyag-saturationdecreaseasafunctionofIQaswellasag-saturationincreasefrommiddleagetosenescence.Specificallyspeaking,forsampleswithameanintelligencethatistwostandarddeviations(i.e.,30IQ-points)higher,themeancorrelationtobeexpectedisdecreasedbyapproximately.15points.Thequestionremainswhetheradifferenceofthismagnitudecouldresultinagreaterapparentfactorialcomplexitywhencognitivedataarefactoredforthehigher-abilitysample,asopposedtothelower-abilitysample.Itseemslikelythatgreaterfactordimensionalityshouldtendtobeobservedforthecaseofhigherability,butthemagnitudeofthiseffect(i.e.,howmuchmorelikelyandhowmanymorefactors)remainsuncertain. Practicalvalidity[edit] Thepracticalvalidityofgasapredictorofeducational,economic,andsocialoutcomesisthesubjectofongoingdebate.[61]Someresearchershavearguedthatitismorefar-ranginganduniversalthananyotherknownpsychologicalvariable,[62]andthatthevalidityofgincreasesasthecomplexityofthemeasuredtaskincreases.[63][64]Othershavearguedthattestsofspecificabilitiesoutperformgfactorinanalysesfittedtoreal-worldsituations.[65][66][67] Atest'spracticalvalidityismeasuredbyitscorrelationwithperformanceonsomecriterionexternaltothetest,suchascollegegrade-pointaverage,oraratingofjobperformance.Thecorrelationbetweentestscoresandameasureofsomecriterioniscalledthevaliditycoefficient.Onewaytointerpretavaliditycoefficientistosquareittoobtainthevarianceaccountedbythetest.Forexample,avaliditycoefficientof.30correspondsto9percentofvarianceexplained.Thisapproachhas,however,beencriticizedasmisleadinganduninformative,andseveralalternativeshavebeenproposed.Onearguablymoreinterpretableapproachistolookatthepercentageoftesttakersineachtestscorequintilewhomeetsomeagreed-uponstandardofsuccess.Forexample,ifthecorrelationbetweentestscoresandperformanceis.30,theexpectationisthat67percentofthoseinthetopquintilewillbeabove-averageperformers,comparedto33percentofthoseinthebottomquintile.[68][69] Academicachievement[edit] Thepredictivevalidityofgismostconspicuousinthedomainofscholasticperformance.Thisisapparentlybecausegiscloselylinkedtotheabilitytolearnnovelmaterialandunderstandconceptsandmeanings.[63] Inelementaryschool,thecorrelationbetweenIQandgradesandachievementscoresisbetween.60and.70.Atmoreadvancededucationallevels,morestudentsfromthelowerendoftheIQdistributiondropout,whichrestrictstherangeofIQsandresultsinlowervaliditycoefficients.Inhighschool,college,andgraduateschoolthevaliditycoefficientsare.50–.60,.40–.50,and.30–.40,respectively.ThegloadingsofIQscoresarehigh,butitispossiblethatsomeofthevalidityofIQinpredictingscholasticachievementisattributabletofactorsmeasuredbyIQindependentofg.AccordingtoresearchbyRobertL.Thorndike,80to90percentofthepredictablevarianceinscholasticperformanceisduetog,withtherestattributedtonon-gfactorsmeasuredbyIQandothertests.[70] AchievementtestscoresaremorehighlycorrelatedwithIQthanschoolgrades.Thismaybebecausegradesaremoreinfluencedbytheteacher'sidiosyncraticperceptionsofthestudent.[71]InalongitudinalEnglishstudy,gscoresmeasuredatage11correlatedwithallthe25subjecttestsofthenationalGCSEexaminationtakenatage16.Thecorrelationsrangedfrom.77forthemathematicstestto.42forthearttest.ThecorrelationbetweengandageneraleducationalfactorcomputedfromtheGCSEtestswas.81.[72] ResearchsuggeststhattheSAT,widelyusedincollegeadmissions,isprimarilyameasureofg.Acorrelationof.82hasbeenfoundbetweengscorescomputedfromanIQtestbatteryandSATscores.Inastudyof165,000studentsat41U.S.colleges,SATscoreswerefoundtobecorrelatedat.47withfirst-yearcollegegrade-pointaverageaftercorrectingforrangerestrictioninSATscores(thecorrelationrisesto.55whencoursedifficultyisheldconstant,i.e.,ifallstudentsattendedthesamesetofclasses).[68][73] Jobattainment[edit] Thereisahighcorrelationof.90to.95betweentheprestigerankingsofoccupations,asratedbythegeneralpopulation,andtheaveragegeneralintelligencescoresofpeopleemployedineachoccupation.Atthelevelofindividualemployees,theassociationbetweenjobprestigeandgislower–onelargeU.S.studyreportedacorrelationof.65(.72correctedforattenuation).Meanlevelofgthusincreaseswithperceivedjobprestige.Ithasalsobeenfoundthatthedispersionofgeneralintelligencescoresissmallerinmoreprestigiousoccupationsthaninlowerleveloccupations,suggestingthathigherleveloccupationshaveminimumgrequirements.[74][75] Jobperformance[edit] Researchindicatesthattestsofgarethebestsinglepredictorsofjobperformance,withanaveragevaliditycoefficientof.55acrossseveralmeta-analysesofstudiesbasedonsupervisorratingsandjobsamples.Theaveragemeta-analyticvaliditycoefficientforperformanceinjobtrainingis.63.[76]Thevalidityofginthehighestcomplexityjobs(professional,scientific,anduppermanagementjobs)hasbeenfoundtobegreaterthaninthelowestcomplexityjobs,butghaspredictivevalidityevenforthesimplestjobs.Researchalsoshowsthatspecificaptitudeteststailoredforeachjobprovidelittleornoincreaseinpredictivevalidityovertestsofgeneralintelligence.Itisbelievedthatgaffectsjobperformancemainlybyfacilitatingtheacquisitionofjob-relatedknowledge.Thepredictivevalidityofgisgreaterthanthatofworkexperience,andincreasedexperienceonthejobdoesnotdecreasethevalidityofg.[63][74] Ina2011meta-analysis,researchersfoundthatgeneralcognitiveability(GCA)predictedjobperformancebetterthanpersonality(Fivefactormodel)andthreestreamsofemotionalintelligence.Theyexaminedtherelativeimportanceoftheseconstructsonpredictingjobperformanceandfoundthatcognitiveabilityexplainedmostofthevarianceinjobperformance.[77]OtherstudiessuggestedthatGCAandemotionalintelligencehavealinearindependentandcomplementarycontributiontojobperformance.CôtéandMiners(2015)[78]foundthattheseconstructsareinterrelatedwhenassessingtheirrelationshipwithtwoaspectsofjobperformance:organisationalcitizenshipbehaviour(OCB)andtaskperformance.EmotionalintelligenceisabetterpredictoroftaskperformanceandOCBwhenGCAislowandviceversa.Forinstance,anemployeewithlowGCAwillcompensatehis/hertaskperformanceandOCB,ifemotionalintelligenceishigh. Althoughthesecompensatoryeffectsfavouremotionalintelligence,GCAstillremainsasthebestpredictorofjobperformance.SeveralresearchershavestudiedthecorrelationbetweenGCAandjobperformanceamongdifferentjobpositions.Forinstance,Ghiselli(1973)[79]foundthatsalespersonshadahighercorrelationthansalesclerk.Theformerobtainedacorrelationof0.61forGCA,0.40forperceptualabilityand0.29forpsychomotorabilities;whereassalesclerkobtainedacorrelationof0.27forGCA,0.22forperceptualabilityand0.17forpsychomotorabilities.[80]OtherstudiescomparedGCA–jobperformancecorrelationbetweenjobsofdifferentcomplexity.HunterandHunter(1984)[81]developedameta-analysiswithover400studiesandfoundthatthiscorrelationwashigherforjobsofhighcomplexity(0.57).Followedbyjobsofmediumcomplexity(0.51)andlowcomplexity(0.38). Jobperformanceismeasuredbyobjectiveratingperformanceandsubjectiveratings.Althoughtheformerisbetterthansubjectiveratings,mostofstudiesinjobperformanceandGCAhavebeenbasedonsupervisorperformanceratings.Thisratingcriterionisconsideredproblematicandunreliable,mainlybecauseofitsdifficultytodefinewhatisagoodandbadperformance.Ratingofsupervisorstendstobesubjectiveandinconsistentamongemployees.[82]Additionally,supervisorratingofjobperformanceisinfluencedbydifferentfactors,suchashaloeffect,[83]facialattractiveness,[84]racialorethnicbias,andheightofemployees.[85]However,Vinchur,Schippmann,SwitzerandRoth(1998)[80]foundintheirstudywithsalesemployeesthatobjectivesalesperformancehadacorrelationof0.04withGCA,whilesupervisorperformanceratinggotacorrelationof0.40.Thesefindingsweresurprising,consideringthatthemaincriterionforassessingtheseemployeeswouldbetheobjectivesales. InunderstandinghowGCAisassociatedjobperformance,severalresearchersconcludedthatGCAaffectsacquisitionofjobknowledge,whichinturnimprovesjobperformance.Inotherwords,peoplehighinGCAarecapabletolearnfasterandacquiremorejobknowledgeeasily,whichallowthemtoperformbetter.Conversely,lackofabilitytoacquirejobknowledgewilldirectlyaffectjobperformance.ThisisduetolowlevelsofGCA.Also,GCAhasadirecteffectonjobperformance.Inadailybasis,employeesareexposedconstantlytochallengesandproblemsolvingtasks,whichsuccessdependssolelyontheirGCA.Thesefindingsarediscouragingforgovernmentalentitiesinchargeofprotectingrightsofworkers.[86]BecauseofthehighcorrelationofGCAonjobperformance,companiesarehiringemployeesbasedonGCAtestsscores.Inevitably,thispracticeisdenyingtheopportunitytoworktomanypeoplewithlowGCA.[87]PreviousresearchershavefoundsignificantdifferencesinGCAbetweenrace/ethnicitygroups.Forinstance,thereisadebatewhetherstudieswerebiasedagainstAfro-Americans,whoscoredsignificantlylowerthanwhiteAmericansinGCAtests.[88]However,findingsonGCA-jobperformancecorrelationmustbetakencarefully.SomeresearchershavewarnedtheexistenceofstatisticalartifactsrelatedtomeasuresofjobperformanceandGCAtestscores.Forexample,Viswesvaran,OnesandSchmidt(1996)[89]arguedthatisquiteimpossibletoobtainperfectmeasuresofjobperformancewithoutincurringinanymethodologicalerror.Moreover,studiesonGCAandjobperformancearealwayssusceptibletorangerestriction,becausedataisgatheredmostlyfromcurrentemployees,neglectingthosethatwerenothired.Hence,samplecomesfromemployeeswhosuccessfullypassedhiringprocess,includingmeasuresofGCA.[90] Income[edit] Thecorrelationbetweenincomeandg,asmeasuredbyIQscores,averagesabout.40acrossstudies.Thecorrelationishigherathigherlevelsofeducationanditincreaseswithage,stabilizingwhenpeoplereachtheirhighestcareerpotentialinmiddleage.Evenwheneducation,occupationandsocioeconomicbackgroundareheldconstant,thecorrelationdoesnotvanish.[91] Othercorrelates[edit] Seealso:Evolutionofhumanintelligence§ Socialexchangetheory,Evolutionaryaesthetics,Evolutionarylinguistics,Evolutionarymusicology,Sexualselectioninhumans,Socialselection,andWasonselectiontask Thegfactorisreflectedinmanysocialoutcomes.Manysocialbehaviorproblems,suchasdroppingoutofschool,chronicwelfaredependency,accidentproneness,andcrime,arenegativelycorrelatedwithgindependentofsocialclassoforigin.[92]Healthandmortalityoutcomesarealsolinkedtog,withhigherchildhoodtestscorespredictingbetterhealthandmortalityoutcomesinadulthood(seeCognitiveepidemiology).[93] In2004,psychologistSatoshiKanazawaarguedthatgwasadomain-specific,species-typical,informationprocessingpsychologicaladaptation,[94]andin2010,Kanazawaarguedthatgcorrelatedonlywithperformanceonevolutionarilyunfamiliarratherthanevolutionarilyfamiliarproblems,proposingwhathetermedthe"Savanna-IQinteractionhypothesis".[95][96]In2006,PsychologicalReviewpublishedacommentreviewingKanazawa's2004articlebypsychologistsDennyBorsboomandConorDolanthatarguedthatKanazawa'sconceptionofgwasempiricallyunsupportedandpurelyhypotheticalandthatanevolutionaryaccountofgmustaddressitasasourceofindividualdifferences,[97]andinresponsetoKanazawa's2010article,psychologistsScottBarryKaufman,ColinG.DeYoung,DeirdreReis,andJeremyR.Graypublishedastudyin2011inIntelligenceof112subjectstakinga70-itemcomputerversionoftheWasonselectiontask(alogicpuzzle)inasocialrelationscontextasproposedbyevolutionarypsychologistsLedaCosmidesandJohnToobyinTheAdaptedMind,[98]andfoundinsteadthat"performanceonnon-arbitrary,evolutionarilyfamiliarproblemsismorestronglyrelatedtogeneralintelligencethanperformanceonarbitrary,evolutionarilynovelproblems".[99][100] Geneticandenvironmentaldeterminants[edit] Mainarticle:HeritabilityofIQ Heritabilityistheproportionofphenotypicvarianceinatraitinapopulationthatcanbeattributedtogeneticfactors.Theheritabilityofghasbeenestimatedtofallbetween40and80percentusingtwin,adoption,andotherfamilystudydesignsaswellasmoleculargeneticmethods.Estimatesbasedonthetotalityofevidenceplacetheheritabilityofgatabout50%.[101]Ithasbeenfoundtoincreaselinearlywithage.Forexample,alargestudyinvolvingmorethan11,000pairsoftwinsfromfourcountriesreportedtheheritabilityofgtobe41percentatagenine,55percentatagetwelve,and66percentatageseventeen.Otherstudieshaveestimatedthattheheritabilityisashighas80percentinadulthood,althoughitmaydeclineinoldage.MostoftheresearchontheheritabilityofghasbeenconductedintheUnitedStatesandWesternEurope,butstudiesinRussia(Moscow),theformerEastGermany,Japan,andruralIndiahaveyieldedsimilarestimatesofheritabilityasWesternstudies.[41][102][103][104] Aswithheritabilityingeneral,theheritabilityofgcanbeunderstoodinreferencetoaspecificpopulationataspecificplaceandtime,andfindingsforonepopulationdonotapplytoadifferentpopulationthatisexposedtodifferentenvironmentalfactors.[105]Apopulationthatisexposedtostrongenvironmentalfactorscanbeexpectedtohavealowerlevelofheritabilitythanapopulationthatisexposedtoonlyweakenvironmentalfactors.Forexample,onetwinstudyfoundthatgenotypedifferencesalmostcompletelyexplainthevarianceinIQscoreswithinaffluentfamilies,butmakeclosetozerocontributiontowardsexplainingIQscoredifferencesinimpoverishedfamilies.[106]Notably,heritabilityfindingsalsoonlyrefertototalvariationwithinapopulationanddonotsupportageneticexplanationfordifferencesbetweengroups.[107]Itistheoreticallypossibleforthedifferencesbetweentheaveragegoftwogroupstobe100%duetoenvironmentalfactorsevenifthevariancewithineachgroupis100%heritable. Behavioralgeneticresearchhasalsoestablishedthattheshared(orbetween-family)environmentaleffectsongarestronginchildhood,butdeclinethereafterandarenegligibleinadulthood.Thisindicatesthattheenvironmentaleffectsthatareimportanttothedevelopmentofgareuniqueandnotsharedbetweenmembersofthesamefamily.[103] Thegeneticcorrelationisastatisticthatindicatestheextenttowhichthesamegeneticeffectsinfluencetwodifferenttraits.Ifthegeneticcorrelationbetweentwotraitsiszero,thegeneticeffectsonthemareindependent,whereasacorrelationof1.0meansthatthesamesetofgenesexplainstheheritabilityofbothtraits(regardlessofhowhighorlowtheheritabilityofeachis).Geneticcorrelationsbetweenspecificmentalabilities(suchasverbalabilityandspatialability)havebeenconsistentlyfoundtobeveryhigh,closeto1.0.Thisindicatesthatgeneticvariationincognitiveabilitiesisalmostentirelyduetogeneticvariationinwhatevergis.Italsosuggeststhatwhatiscommonamongcognitiveabilitiesislargelycausedbygenes,andthatindependenceamongabilitiesislargelyduetoenvironmentaleffects.Thusithasbeenarguedthatwhengenesforintelligenceareidentified,theywillbe"generalistgenes",eachaffectingmanydifferentcognitiveabilities.[103][108][109] Muchresearchpointstogbeingahighlypolygenictraitinfluencedbymanycommongeneticvariants,eachhavingonlysmalleffects.Anotherpossibilityisthatheritabledifferencesingareduetoindividualshavingdifferent"loads"ofrare,deleteriousmutations,withgeneticvariationamongindividualspersistingduetomutation–selectionbalance.[109][110] Anumberofcandidategeneshavebeenreportedtobeassociatedwithintelligencedifferences,buttheeffectsizeshavebeensmallandalmostnoneofthefindingshavebeenreplicated.Noindividualgeneticvariantshavebeenconclusivelylinkedtointelligenceinthenormalrangesofar.Manyresearchersbelievethatverylargesampleswillbeneededtoreliablydetectindividualgeneticpolymorphismsassociatedwithg.[41][110]However,whilegenesinfluencingvariationinginthenormalrangehaveprovendifficulttofind,manysingle-genedisorderswithintellectualdisabilityamongtheirsymptomshavebeendiscovered.[111] Ithasbeensuggestedthatthegloadingofmentaltestshavebeenfoundtocorrelatewithheritability,[34]butboththeempiricaldataandstatisticalmethodologybearingonthisquestionaremattersofactivecontroversy.[112][113][114]Severalstudiessuggestthattestswithlargergloadingsaremoreaffectedbyinbreedingdepressionloweringtestscores.[citationneeded]Thereisalsoevidencethattestswithlargergloadingsareassociatedwithlargerpositiveheteroticeffectsontestscores,whichhasbeensuggestedtoindicatethepresenceofgeneticdominanceeffectsforg.[115] Neuroscientificfindings[edit] Mainarticle:Neuroscienceandintelligence ghasanumberofcorrelatesinthebrain.Studiesusingmagneticresonanceimaging(MRI)haveestablishedthatgandtotalbrainvolumearemoderatelycorrelated(r~.3–.4).Externalheadsizehasacorrelationof~.2withg.MRIresearchonbrainregionsindicatesthatthevolumesoffrontal,parietalandtemporalcortices,andthehippocampusarealsocorrelatedwithg,generallyat.25ormore,whilethecorrelations,averagedovermanystudies,withoverallgreymatterandoverallwhitematterhavebeenfoundtobe.31and.27,respectively.Somebutnotallstudieshavealsofoundpositivecorrelationsbetweengandcorticalthickness.However,theunderlyingreasonsfortheseassociationsbetweenthequantityofbraintissueanddifferencesincognitiveabilitiesremainlargelyunknown.[2] Mostresearchersbelievethatintelligencecannotbelocalizedtoasinglebrainregion,suchasthefrontallobe.Brainlesionstudieshavefoundsmallbutconsistentassociationsindicatingthatpeoplewithmorewhitematterlesionstendtohavelowercognitiveability.ResearchutilizingNMRspectroscopyhasdiscoveredsomewhatinconsistentbutgenerallypositivecorrelationsbetweenintelligenceandwhitematterintegrity,supportingthenotionthatwhitematterisimportantforintelligence.[2] Someresearchsuggeststhatasidefromtheintegrityofwhitematter,alsoitsorganizationalefficiencyisrelatedtointelligence.ThehypothesisthatbrainefficiencyhasaroleinintelligenceissupportedbyfunctionalMRIresearchshowingthatmoreintelligentpeoplegenerallyprocessinformationmoreefficiently,i.e.,theyusefewerbrainresourcesforthesametaskthanlessintelligentpeople.[2] Smallbutrelativelyconsistentassociationswithintelligencetestscoresincludealsobrainactivity,asmeasuredbyEEGrecordsorevent-relatedpotentials,andnerveconductionvelocity.[116][117] ginnon-humans[edit] Mainarticle:gfactorinnon-humans Evidenceofageneralfactorofintelligencehasalsobeenobservedinnon-humananimals.Studieshaveshownthatgisresponsiblefor47%ofthevarianceatthespecieslevelinprimates[118]andaround55%oftheindividualvarianceobservedinmice.[119][120]Areviewandmeta-analysisofgeneralintelligence,however,foundthattheaveragecorrelationamongcognitiveabilitieswas0.18andsuggestedthatoverallsupportforgisweakinnon-humananimals.[121] Whilenotabletobeassessedusingthesameintelligencemeasuresusedinhumans,cognitiveabilitycanbemeasuredwithavarietyofinteractiveandobservationaltoolsfocusingoninnovation,habitreversal,sociallearning,andresponsestonovelty.Non-humanmodelsofgsuchasmiceareusedtostudygeneticinfluencesonintelligenceandneurologicaldevelopmentalresearchintothemechanismsbehindandbiologicalcorrelatesofg.[122] g(orc)inhumangroups[edit] Mainarticle:CollectiveintelligenceSimilartogforindividuals,anewresearchpathaimstoextractageneralcollectiveintelligencefactorcforgroupsdisplayingagroup'sgeneralabilitytoperformawiderangeoftasks.[123]Definition,operationalizationandstatisticalapproachforthiscfactorarederivedfromandsimilartog.Causes,predictivevalidityaswellasadditionalparallelstogareinvestigated.[124] Otherbiologicalassociations[edit] Heightiscorrelatedwithintelligence(r~.2),butthiscorrelationhasnotgenerallybeenfoundwithinfamilies(i.e.,amongsiblings),suggestingthatitresultsfromcross-assortativematingforheightandintelligence,orfromanotherfactorthatcorrelateswithboth(e.g.nutrition).Myopiaisknowntobeassociatedwithintelligence,withacorrelationofaround.2to.25,andthisassociationhasbeenfoundwithinfamilies,too.[125] Groupsimilaritiesanddifferences[edit] Seealso:SexdifferencesinintelligenceandRaceandintelligence Cross-culturalstudiesindicatethatthegfactorcanbeobservedwheneverabatteryofdiverse,complexcognitivetestsisadministeredtoahumansample.ThefactorstructureofIQtestshasalsobeenfoundtobeconsistentacrosssexesandethnicgroupsintheU.S.andelsewhere.[117]Thegfactorhasbeenfoundtobethemostinvariantofallfactorsincross-culturalcomparisons.Forexample,whenthegfactorscomputedfromanAmericanstandardizationsampleofWechsler'sIQbatteryandfromlargesampleswhocompletedtheJapanesetranslationofthesamebatterywerecompared,thecongruencecoefficientwas.99,indicatingvirtualidentity.Similarly,thecongruencecoefficientbetweenthegfactorsobtainedfromwhiteandblackstandardizationsamplesoftheWISCbatteryintheU.S.was.995,andthevarianceintestscoresaccountedforbygwashighlysimilarforbothgroups.[126] Moststudiessuggestthattherearenegligibledifferencesinthemeanlevelofgbetweenthesexes,butthatsexdifferencesincognitiveabilitiesaretobefoundinmorenarrowdomains.Forexample,malesgenerallyoutperformfemalesinspatialtasks,whilefemalesgenerallyoutperformmalesinverbaltasks.[127]Anotherdifferencethathasbeenfoundinmanystudiesisthatmalesshowmorevariabilityinbothgeneralandspecificabilitiesthanfemales,withproportionatelymoremalesatboththelowendandthehighendofthetestscoredistribution.[128] Differencesingbetweenracialandethnicgroupshavebeenfound,particularlyintheU.S.betweenblack-andwhite-identifyingtesttakers,thoughthesedifferencesappeartohavediminishedsignificantlyovertime,[113]andtobeattributabletoenvironmental(ratherthangenetic)causes.[113][129]Someresearchershavesuggestedthatthemagnitudeoftheblack-whitegapincognitivetestresultsisdependentonthemagnitudeofthetest'sgloading,withtestsshowinghighergloadingproducinglargergaps(seeSpearman'shypothesis),[130]whileothershavecriticizedthisviewasmethodologicallyunfounded.[131][132]StillothershavenotedthatdespitetheincreasinggloadingofIQtestbatteriesovertime,theperformancegapbetweenracialgroupscontinuestodiminish.[113]Comparativeanalysishasshownthatwhileagapofapproximately1.1standarddeviationinmeanIQ(around16points)betweenwhiteandblackAmericansexistedinthelate1960s,between1972and2002blackAmericansgainedbetween4and7IQpointsrelativetonon-HispanicWhites,andthat"theggapbetweenBlacksandWhitesdeclinedvirtuallyintandemwiththeIQgap."[113]Incontrast,AmericansofEastAsiandescentgenerallyslightlyoutscorewhiteAmericans.[133]IthasbeenclaimedthatracialandethnicdifferencessimilartothosefoundintheU.S.canbeobservedglobally,[134]butthesignificance,methodologicalgrounding,andtruthofsuchclaimshaveallbeendisputed.[135][136][137][138][139][140] Relationtootherpsychologicalconstructs[edit] Elementarycognitivetasks[edit] Mainarticles:ElementarycognitivetaskandMentalchronometry AnillustrationoftheJensenbox,anapparatusformeasuringchoicereactiontime. Elementarycognitivetasks(ECTs)alsocorrelatestronglywithg.ECTsare,asthenamesuggests,simpletasksthatapparentlyrequireverylittleintelligence,butstillcorrelatestronglywithmoreexhaustiveintelligencetests.DeterminingwhetheralightisredorblueanddeterminingwhethertherearefourorfivesquaresdrawnonacomputerscreenaretwoexamplesofECTs.Theanswerstosuchquestionsareusuallyprovidedbyquicklypressingbuttons.Often,inadditiontobuttonsforthetwooptionsprovided,athirdbuttonishelddownfromthestartofthetest.Whenthestimulusisgiventothesubject,theyremovetheirhandfromthestartingbuttontothebuttonofthecorrectanswer.Thisallowstheexaminertodeterminehowmuchtimewasspentthinkingabouttheanswertothequestion(reactiontime,usuallymeasuredinsmallfractionsofsecond),andhowmuchtimewasspentonphysicalhandmovementtothecorrectbutton(movementtime).Reactiontimecorrelatesstronglywithg,whilemovementtimecorrelateslessstrongly.[141] ECTtestinghasallowedquantitativeexaminationofhypothesesconcerningtestbias,subjectmotivation,andgroupdifferences.Byvirtueoftheirsimplicity,ECTsprovidealinkbetweenclassicalIQtestingandbiologicalinquiriessuchasfMRIstudies. Workingmemory[edit] Onetheoryholdsthatgisidenticalornearlyidenticaltoworkingmemorycapacity.Amongotherevidenceforthisview,somestudieshavefoundfactorsrepresentinggandworkingmemorytobeperfectlycorrelated.However,inameta-analysisthecorrelationwasfoundtobeconsiderablylower.[142]Onecriticismthathasbeenmadeofstudiesthatidentifygwithworkingmemoryisthat"wedonotadvanceunderstandingbyshowingthatonemysteriousconceptislinkedtoanother."[143] Piagetiantasks[edit] Psychometrictheoriesofintelligenceaimatquantifyingintellectualgrowthandidentifyingabilitydifferencesbetweenindividualsandgroups.Incontrast,JeanPiaget'stheoryofcognitivedevelopmentseekstounderstandqualitativechangesinchildren'sintellectualdevelopment.Piagetdesignedanumberoftaskstoverifyhypothesesarisingfromhistheory.Thetaskswerenotintendedtomeasureindividualdifferences,andtheyhavenoequivalentinpsychometricintelligencetests.[144][145]Forexample,inoneofthebest-knownPiagetianconservationtasksachildisaskediftheamountofwaterintwoidenticalglassesisthesame.Afterthechildagreesthattheamountisthesame,theinvestigatorpoursthewaterfromoneoftheglassesintoaglassofdifferentshapesothattheamountappearsdifferentalthoughitremainsthesame.Thechildisthenaskediftheamountofwaterinthetwoglassesisthesameordifferent. NotwithstandingthedifferentresearchtraditionsinwhichpsychometrictestsandPiagetiantasksweredeveloped,thecorrelationsbetweenthetwotypesofmeasureshavebeenfoundtobeconsistentlypositiveandgenerallymoderateinmagnitude.Acommongeneralfactorunderliesthem.IthasbeenshownthatitispossibletoconstructabatteryconsistingofPiagetiantasksthatisasgoodameasureofgasstandardIQtests.[144][146] Personality[edit] Mainarticle:Intelligenceandpersonality Thetraditionalviewinpsychologyisthatthereisnomeaningfulrelationshipbetweenpersonalityandintelligence,andthatthetwoshouldbestudiedseparately.Intelligencecanbeunderstoodintermsofwhatanindividualcando,orwhathisorhermaximalperformanceis,whilepersonalitycanbethoughtofintermsofwhatanindividualwilltypicallydo,orwhathisorhergeneraltendenciesofbehaviorare.Researchhasindicatedthatcorrelationsbetweenmeasuresofintelligenceandpersonalityaresmall,andithasthusbeenarguedthatgisapurelycognitivevariablethatisindependentofpersonalitytraits.Ina2007meta-analysisthecorrelationsbetweengandthe"BigFive"personalitytraitswerefoundtobeasfollows: conscientiousness−.04 agreeableness.00 extraversion.02 openness.22 emotionalstability.09 Thesamemeta-analysisfoundacorrelationof.20betweenself-efficacyandg.[147][148][149] Someresearchershavearguedthattheassociationsbetweenintelligenceandpersonality,albeitmodest,areconsistent.Theyhaveinterpretedcorrelationsbetweenintelligenceandpersonalitymeasuresintwomainways.Thefirstperspectiveisthatpersonalitytraitsinfluenceperformanceonintelligencetests.Forexample,apersonmayfailtoperformatamaximallevelonanIQtestduetohisorheranxietyandstress-proneness.Thesecondperspectiveconsidersintelligenceandpersonalitytobeconceptuallyrelated,withpersonalitytraitsdetermininghowpeopleapplyandinvesttheircognitiveabilities,leadingtoknowledgeexpansionandgreatercognitivedifferentiation.[147][150] Creativity[edit] Someresearchersbelievethatthereisathresholdlevelofgbelowwhichsociallysignificantcreativityisrare,butthatotherwisethereisnorelationshipbetweenthetwo.Ithasbeensuggestedthatthisthresholdisatleastonestandarddeviationabovethepopulationmean.Abovethethreshold,personalitydifferencesarebelievedtobeimportantdeterminantsofindividualvariationincreativity.[151][152] Othershavechallengedthethresholdtheory.Whilenotdisputingthatopportunityandpersonalattributesotherthanintelligence,suchasenergyandcommitment,areimportantforcreativity,theyarguethatgispositivelyassociatedwithcreativityevenatthehighendoftheabilitydistribution.ThelongitudinalStudyofMathematicallyPrecociousYouthhasprovidedevidenceforthiscontention.Ithasshowedthatindividualsidentifiedbystandardizedtestsasintellectuallygiftedinearlyadolescenceaccomplishcreativeachievements(forexample,securingpatentsorpublishingliteraryorscientificworks)atseveraltimestherateofthegeneralpopulation,andthatevenwithinthetop1percentofcognitiveability,thosewithhigherabilityaremorelikelytomakeoutstandingachievements.Thestudyhasalsosuggestedthatthelevelofgactsasapredictorofthelevelofachievement,whilespecificcognitiveabilitypatternspredicttherealmofachievement.[153][154] Challenges[edit] Gf-Gctheory[edit] Mainarticle:Fluidandcrystallizedintelligence RaymondCattell,astudentofCharlesSpearman's,rejectedtheunitarygfactormodelanddividedgintotwobroad,relativelyindependentdomains:fluidintelligence(Gf)andcrystallizedintelligence(Gc).Gfisconceptualizedasacapacitytofigureoutnovelproblems,anditisbestassessedwithtestswithlittleculturalorscholasticcontent,suchasRaven'smatrices.Gccanbethoughtofasconsolidatedknowledge,reflectingtheskillsandinformationthatanindividualacquiresandretainsthroughouthisorherlife.Gcisdependentoneducationandotherformsofacculturation,anditisbestassessedwithteststhatemphasizescholasticandculturalknowledge.[2][45][155]Gfcanbethoughttoprimarilyconsistofcurrentreasoningandproblemsolvingcapabilities,whileGcreflectstheoutcomeofpreviouslyexecutedcognitiveprocesses.[156] TherationalefortheseparationofGfandGcwastoexplainindividuals'cognitivedevelopmentovertime.WhileGfandGchavebeenfoundtobehighlycorrelated,theydifferinthewaytheychangeoveralifetime.Gftendstopeakataroundage20,slowlydecliningthereafter.Incontrast,Gcisstableorincreasesacrossadulthood.Asinglegeneralfactorhasbeencriticizedasobscuringthisbifurcatedpatternofdevelopment.CattellarguedthatGfreflectedindividualdifferencesintheefficiencyofthecentralnervoussystem.Gcwas,inCattell'sthinking,theresultofaperson"investing"hisorherGfinlearningexperiencesthroughoutlife.[2][31][45][157] Cattell,togetherwithJohnHorn,laterexpandedtheGf-Gcmodeltoincludeanumberofotherbroadabilities,suchasGq(quantitativereasoning)andGv(visual-spatialreasoning).WhileallthebroadabilityfactorsintheextendedGf-Gcmodelarepositivelycorrelatedandthuswouldenabletheextractionofahigherordergfactor,CattellandHornmaintainedthatitwouldbeerroneoustopositthatageneralfactorunderliesthesebroadabilities.Theyarguedthatgfactorscomputedfromdifferenttestbatteriesarenotinvariantandwouldgivedifferentvaluesofg,andthatthecorrelationsamongtestsarisebecauseitisdifficulttotestjustoneabilityatatime.[2][49][158] However,severalresearchershavesuggestedthattheGf-Gcmodeliscompatiblewithag-centeredunderstandingofcognitiveabilities.Forexample,JohnB.Carroll'sthree-stratummodelofintelligenceincludesbothGfandGctogetherwithahigher-ordergfactor.Basedonfactoranalysesofmanydatasets,someresearchershavealsoarguedthatGfandgareoneandthesamefactorandthatgfactorsfromdifferenttestbatteriesaresubstantiallyinvariantprovidedthatthebatteriesarelargeanddiverse.[45][159][160] Theoriesofuncorrelatedabilities[edit] Severaltheoristshaveproposedthatthereareintellectualabilitiesthatareuncorrelatedwitheachother.AmongtheearliestwasL.L.Thurstonewhocreatedamodelofprimarymentalabilitiesrepresentingsupposedlyindependentdomainsofintelligence.However,Thurstone'stestsoftheseabilitieswerefoundtoproduceastronggeneralfactor.Hearguedthatthelackofindependenceamonghistestsreflectedthedifficultyofconstructing"factoriallypure"teststhatmeasuredjustoneability.Similarly,J.P.Guilfordproposedamodelofintelligencethatcomprisedupto180distinct,uncorrelatedabilities,andclaimedtobeabletotestallofthem.LateranalyseshaveshownthatthefactorialproceduresGuilfordpresentedasevidenceforhistheorydidnotprovidesupportforit,andthatthetestdatathatheclaimedprovidedevidenceagainstgdidinfactexhibittheusualpatternofintercorrelationsaftercorrectionforstatisticalartifacts.[161][162] Morerecently,HowardGardnerhasdevelopedthetheoryofmultipleintelligences.Hepositstheexistenceofninedifferentandindependentdomainsofintelligence,suchasmathematical,linguistic,spatial,musical,bodily-kinesthetic,meta-cognitive,andexistentialintelligences,andcontendsthatindividualswhofailinsomeofthemmayexcelinothers.AccordingtoGardner,testsandschoolstraditionallyemphasizeonlylinguisticandlogicalabilitieswhileneglectingotherformsofintelligence.Whilepopularamongeducationalists,Gardner'stheoryhasbeenmuchcriticizedbypsychologistsandpsychometricians.Onecriticismisthatthetheorydoesviolencetobothscientificandeverydayusagesoftheword"intelligence."SeveralresearchershavearguedthatnotallofGardner'sintelligencesfallwithinthecognitivesphere.Forexample,Gardnercontendsthatasuccessfulcareerinprofessionalsportsorpopularmusicreflectsbodily-kinestheticintelligenceandmusicalintelligence,respectively,eventhoughonemightusuallytalkofathleticandmusicalskills,talents,orabilitiesinstead.AnothercriticismofGardner'stheoryisthatmanyofhispurportedlyindependentdomainsofintelligenceareinfactcorrelatedwitheachother.Respondingtoempiricalanalysesshowingcorrelationsbetweenthedomains,Gardnerhasarguedthatthecorrelationsexistbecauseofthecommonformatoftestsandbecausealltestsrequirelinguisticandlogicalskills.HiscriticshaveinturnpointedoutthatnotallIQtestsareadministeredinthepaper-and-pencilformat,thatasidefromlinguisticandlogicalabilities,IQtestbatteriescontainalsomeasuresof,forexample,spatialabilities,andthatelementarycognitivetasks(forexample,inspectiontimeandreactiontime)thatdonotinvolvelinguisticorlogicalreasoningcorrelatewithconventionalIQbatteries,too.[72][163][164][165] RobertSternberg,workingwithvariouscolleagues,hasalsosuggestedthatintelligencehasdimensionsindependentofg.Hearguesthattherearethreeclassesofintelligence:analytic,practical,andcreative.AccordingtoSternberg,traditionalpsychometrictestsmeasureonlyanalyticintelligence,andshouldbeaugmentedtotestcreativeandpracticalintelligenceaswell.Hehasdevisedseveralteststothiseffect.Sternbergequatesanalyticintelligencewithacademicintelligence,andcontrastsitwithpracticalintelligence,definedasanabilitytodealwithill-definedreal-lifeproblems.Tacitintelligenceisanimportantcomponentofpracticalintelligence,consistingofknowledgethatisnotexplicitlytaughtbutisrequiredinmanyreal-lifesituations.Assessingcreativityindependentofintelligencetestshastraditionallyproveddifficult,butSternbergandcolleagueshaveclaimedtohavecreatedvalidtestsofcreativity,too.ThevalidationofSternberg'stheoryrequiresthatthethreeabilitiestestedaresubstantiallyuncorrelatedandhaveindependentpredictivevalidity.Sternberghasconductedmanyexperimentswhichheclaimsconfirmthevalidityofhistheory,butseveralresearchershavedisputedthisconclusion.Forexample,inhisreanalysisofavalidationstudyofSternberg'sSTATtest,NathanBrodyshowedthatthepredictivevalidityoftheSTAT,atestofthreeallegedlyindependentabilities,wasalmostsolelyduetoasinglegeneralfactorunderlyingthetests,whichBrodyequatedwiththegfactor.[166][167] Flynn'smodel[edit] JamesFlynnhasarguedthatintelligenceshouldbeconceptualizedatthreedifferentlevels:brainphysiology,cognitivedifferencesbetweenindividuals,andsocialtrendsinintelligenceovertime.Accordingtothismodel,thegfactorisausefulconceptwithrespecttoindividualdifferencesbutitsexplanatorypowerislimitedwhenthefocusofinvestigationiseitherbrainphysiology,or,especially,theeffectofsocialtrendsonintelligence.Flynnhascriticizedthenotionthatcognitivegainsovertime,ortheFlynneffect,are"hollow"iftheycannotbeshowntobeincreasesing.HearguesthattheFlynneffectreflectsshiftingsocialprioritiesandindividuals'adaptationtothem.ToapplytheindividualdifferencesconceptofgtotheFlynneffectistoconfusedifferentlevelsofanalysis.Ontheotherhand,accordingtoFlynn,itisalsofallacioustodeny,byreferringtotrendsinintelligenceovertime,thatsomeindividualshave"betterbrainsandminds"tocopewiththecognitivedemandsoftheirparticulartime.Atthelevelofbrainphysiology,Flynnhasemphasizedboththatlocalizedneuralclusterscanbeaffecteddifferentlybycognitiveexercise,andthatthereareimportantfactorsthataffectallneuralclusters.[168] TheMismeasureofMan[edit] PerhapsthemostfamouscritiqueoftheconstructofgisthatofthepaleontologistandbiologistStephenJayGould,presentedinhis1981bookTheMismeasureofMan.Hearguedthatpsychometriciansfallaciouslyreifiedthegfactorintoanineluctable"thing"thatprovidedaconvenientexplanationforhumanintelligence,groundedonlyinmathematicaltheoryratherthantherigorousapplicationofmathematicaltheorytobiologicalknowledge.[169]AnexampleisprovidedintheworkofCyrilBurt,publishedposthumouslyin1972:"Thetwomainconclusionswehavereachedseemclearandbeyondallquestion.Thehypothesisofageneralfactorenteringintoeverytypeofcognitiveprocess,tentativelysuggestedbyspeculationsderivedfromneurologyandbiology,isfullyborneoutbythestatisticalevidence;andthecontentionthatdifferencesinthisgeneralfactordependlargelyontheindividual'sgeneticconstitutionappearsincontestable.Theconceptofaninnate,generalcognitiveability,whichfollowsfromthesetwoassumptions,thoughadmittedlysheerlyanabstraction,isthuswhollyconsistentwiththeempiricalfacts."[170]Spearman'sgandtheconceptofinherited,immutableintelligencewereaboonforeugenicistsandpseudoscientistsalike.[171] CritiqueofGould[citationneeded][edit] ManyresearchershavecriticizedGould'sarguments.Forexample,theyhaverejectedtheaccusationofreification,maintainingthattheuseofextractedfactorssuchasgaspotentialcausalvariableswhoserealitycanbesupportedorrejectedbyfurtherinvestigationsconstitutesanormalscientificpracticethatinnowaydistinguishespsychometricsfromothersciences[clarificationneeded][citationneeded].CriticshavealsosuggestedthatGoulddidnotunderstandthepurposeoffactoranalysis,andthathewasignorantofrelevantmethodologicaladvancesinthefield[citationneeded].Whiledifferentfactorsolutionsmaybemathematicallyequivalentintheirabilitytoaccountforintercorrelationsamongtests,solutionsthatyieldagfactorarepsychologicallypreferableforseveralreasonsextrinsictofactoranalysis,includingthephenomenonofthepositivemanifold,thefactthatthesamegcanemergefromquitedifferenttestbatteries,thewidespreadpracticalvalidityofg,andthelinkageofgtomanybiologicalvariables.[38][39][172] Othercritiquesofg[edit] JohnHornandJohnMcArdlehavearguedthatthemoderngtheory,asespousedby,forexample,ArthurJensen,isunfalsifiable,becausetheexistenceofacommonfactorlikegfollowstautologicallyfrompositivecorrelationsamongtests.TheycontrastedthemodernhierarchicaltheoryofgwithSpearman'soriginaltwo-factortheorywhichwasreadilyfalsifiable(andindeedwasfalsified).[31] JosephGravesJr.andAmandaJohnsonhavearguedthatg"...istothepsychometricianswhatHuygens'etherwastoearlyphysicists:anonentitytakenasanarticleoffaithinsteadofoneinneedofverificationbyrealdata."[173] Seealso[edit] CharlesSpearman –Englishpsychologist(1863–1945) Factoranalysisinpsychometrics –Statisticalmethod Fluidandcrystallizedintelligence –Factorsofgeneralintelligence Flynneffect –20th-centuryriseinoverallhumanintelligence Intelligence –Abilitytoperceive,infer,retainorapplyinformation Intelligencequotient –Scorefromatestdesignedtoassessintelligence Malleabilityofintelligence Spearman'shypothesis Eugenics –Aimtoimproveperceivedhumangeneticquality 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Weinberg,R.A.(1989)."IntelligenceandIQ.LandmarkIssuesandGreatDebates".AmericanPsychologist.44(2):98–104.doi:10.1037/0003-066X.44.2.98. vteHumanintelligencetopicsTypes Collective Emotional Intellectual Linguistic Multiple Social Spatial (visuospatial) Abilities,traits,andconstructs Cognition Communication Creativity Fluidandcrystallizedintelligence gfactor Intelligencequotient Knowledge Learning Memory Problemsolving Reasoning Thought (abstraction) Understanding Visualprocessing Modelsandtheories Cattell–Horn–Carrolltheory Fluidandcrystallizedintelligence Multiple-intelligencestheory Three-stratumtheory Triarchictheory PASStheory Areasofresearch Evolutionofhumanintelligence HeritabilityofIQ Psychometrics Intelligenceandenvironment /fertility /height /health /longevity /neuroscience /personality /race /sex Outlineofhumanintelligence /thought vteEvolutionarypsychology History Theoreticalfoundations Criticism Processes Adaptations Altruism Reciprocal Baldwineffect By-products 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