Bourne a Helen C Fox Ian J Deary Lawrence J Whalley School of Psychology University of Dundee Scotland UK Department of Mental Health University of Aberdeen Scotland UK Department of Psychology University of Edinburgh Scotland UK Received 24 Apri ID: 73832
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Doeschildhoodintelligencepredictvariationincognitivechangeinlaterlife?VictoriaJ.Bourne,HelenC.Fox,IanJ.Deary,LawrenceJ.WhalleySchoolofPsychology,UniversityofDundee,Scotland,UKDepartmentofMentalHealth,UniversityofAberdeen,Scotland,UKDepartmentofPsychology,UniversityofEdinburgh,Scotland,UKReceived24April2006;receivedinrevisedform13October2006;accepted26October2006Availableonline13December2006AbstractLowerchildhoodcognitiveabilitymaybeariskfactorforgreatercognitivedeclineinlatelifeandpro-gressiontodementia.Toassessvariationinage-relatedcognitivechange,itishelpfultohavevalidmea-suresofcognitiveabilityfromearlylife.Here,weexaminetherelationbetweenchildhoodintelligenceandcognitivechangeinlaterlifeintwosamples,onebornin1921andtheotherin1936.Allparticipantscompletedthesametestofmentalability(oneoftheMorayHouseTestseries)atageabout11years,andwerere-examinedonRavensProgressiveMatricesatage77(1921-born)orage64(1936-born).Wherepos-sible,the1921samplewasre-testedattheageofabout80yearsoldandthe1936samplere-testedatabout66years.Aftertakingintoaccountvariouscovariates,includingsex,educationandoccupation,childhoodintelligencewasasignicantpredictorofcognitivechangeinlaterlife.Resultswereinthedirectionthatparticipantswithlowerchildhoodmentalabilityexperiencedrelativelygreatercognitivedecline,whereasthoseofhigherchildhoodmentalabilityshowedimprovedperformance.Thisresultsuggeststhathigherpremorbidcognitiveabilityisprotectiveofdeclineinlaterlife.2006ElsevierLtd.Allrightsreserved.Ageing;Childhoodcognitiveability;Cognitivedecline0191-8869/$-seefrontmatter2006ElsevierLtd.Allrightsreserved. Correspondingauthor.Tel.:+441328384617.E-mailaddress:(V.J.Bourne).www.elsevier.com/locate/paid PersonalityandIndividualDierences42(2007)1551 1559 (14%)refusedtoattendthesecondwaveoftestingwithoutprovidingareason,20people(4%)didnotattendastheyhadmovedoutofthearea,17people(3%)haddied,19people(4%)didnotattendduetopersonalcircumstancesand32people(6%)wereunabletoprovidecompletedatasets.Datawereanalysedusingmultiplelinearregression,withRPMatwavetwoastheoutcomevariable.RPMatwaveonewastherstvariableenteredintothemodel.Thesecondblockcom-prisedanumberofcovariates,enteredsimultaneously,thatmaybeimplicatedincognitiveageingand/ordementia:sex(Dearyetal.,2004),yearsofeducation(Sta,Murray,Deary,&Whalley,),highestoccupationalstatus(Li,Wu,&Sung,2002),whethertheywereasmokeratwaveoneoftesting(Whalley,Fox,Deary,&Starr,2005)andunitsofalcoholconsumedaweekatwaveoneoftesting(Richards,Hardy,&Wadsworth,2005).Cohort(SMS32orSMS47)andintervalbetweentestingsessionindayswerealsoincludedaspossiblecovariates.Childhoodcognitiveabilitywasthenenteredintothemodelinaseparateblock.Byrunningtheanalysisinthisway,thevarianceinRPMatwavetwothatisaccountedforbyperformanceonRPMatwaveone(i.e.,thechangeincognitiveabilityfromwaveonetowavetwo)isanalysedwithintherstblockandpossiblecovariatesaretakenintoaccountinthesecondblock.Signicantndingsinthethirdblockcansubsequentlybeinterpretedaspredictorsofchangeincognitiveabilityfromwaveonetowavetwo,afterstatisticallycontrollingforanyvarianceexplainedbythecovariates.3.ResultsDescriptivestatisticsofthemeasurescanbeseeninTable1.Asummaryoftheregressionanal-ysisispresentedinTable2.RPMatwaveonewasasignicantpredictorofRPMatwavetwo Table1Demographicandcognitivecharacteristicsofthetwosamples,bornineither1921or1936MenWomenTotal1921BirthsampleN464591MHT(11years)42.2(13.3)43.1(10.6)42.6(12.0)RPM(77years)31.3(8.7)29.1(8.0)30.2(8.4)MMSE(77years)28.5(1.7)28.9(1.2)28.7(1.5)RPM(80years)30.6(8.3)29.3(8.3)30.0(8.2)MMSE(80years)28.1(1.8)28.4(1.5)28.3(1.7)ChangeinRPMscore.70(6.7).18(5.7).26(6.2)1936BirthsampleN166183349MHT(11years)43.2(12.6)44.6(12.0)44.0(12.3)RPM(64years)38.0(7.7)36.2(8.7)37.0(8.3)MMSE(64years)29.0(1.4)29.0(1.3)29.0(1.4)RPM(66years)38.4(8.1)36.4(8.7)37.4(8.5)MMSE(66years)28.8(1.4)28.9(1.2)28.8(1.3)ChangeinRPMscore.45(5.2).26(4.9).35(5.0)Allscoresareexpressedasmeans(SD)ofrawscores.MaximumscoreontheMorayHouseTest(MHT)was76,ontheMiniMentalStateExamination(MMSE)was30,andonRavensProgressiveMatrices(RPM)was60.V.J.Bourneetal./PersonalityandIndividualDierences42(2007)1551 1559 =.84,.001)accountingfor67.2%ofthevariance.Withinthecovariatesblockonlyyearsofeducation(=.28,=.048)wassignicant,cohortapproachedsignicance(=1.7,=.053)andallothercovariateswerenotsignicant(&#x-249;&#x.600;.1forall).Thecovariatesaccountedforafurther1.5%ofthevariance.Participantswithfeweryearsofeducationtendedtoshowgreatercognitivedeclineandindividualsfromthe1921birthsampleshowedgreaterdeclinethanthosefromthe1936birthsample.Childhoodcognitivetestscorewasenteredintothethirdblockandwasasig-nicantpredictor(=.13,.001)explainingafurther2%ofthevariance.BecausethevarianceexplainedbyperformanceonRPMatwaveonehasalreadybeentakenintoaccountinthestblock,thisthirdblockcanbeinterpretedintermsofchildhoodcognitiveabilitypredictingchangeincognitiveabilityfromwaveonetowavetwo.Thereisapositiverelationshipbetweenthetwovariables(evidentinthecoecient).Assuch,witheachincreaseofonepointontheMHT,anindividualsperformanceonRPMatwavetwowouldbeexpectedtoincreaseby.13,overandabovethevarianceexplainedbyRPMatwaveone.Therefore,thehigheranindividualschild-hoodcognitiveability,thegreatertheirimprovementinperformancefromwaveonetowavetwo.Inordertoexaminewhetherthisrelationshipwasapparentinbothcohorts,partialcorrela-tionsbetweenchildhoodcognitiveabilityandtherawchangescore,controllingforeachofthevariablescontrolledforintheregressionanalysis,wereconductedforeachofthecohortssepa-rately.Asignicantcorrelationwasfoundforbothcohorts(SMS32:(82)=.315,=.003;(335)=.231,.001)indicatingthattherelationshipbetweenchildhoodcognitiveabil-ityandchangeincognitiveabilityinlaterlifeistrueofbothsamples,althoughstrongerintheSMS32sample.Itispossiblethatourndingsmayhavebeeninatedbytheinclusionofpossibledementiacasesorbyindividualswhohaveshowndramaticcognitivedeclinebetweenthewavesoftesting.Childhoodcognitiveabilityispredictiveofincreasedriskofdementia(Whalleyetal.,2000).Itispossiblethattherelationshipwehaveidentiedmaynotexistforallparticipants,butratheronlyinmoreextremecasesofcognitivedecline.Doestherelationshipbetweenchildhoodcognitiveabilityandchangeincognitiveperformanceinlaterliferemainforparticipantswhoshownosigns Table2FindingsfromthemultipleregressionanalysisBlocksignicanceBlockone:RPMatwaveone.84229.80(1,433)=888.3,.001Blocktwo:Cohort1.6601.94.053(7,426)=2.9,=.006.98.326Interval(days).001.47.640Yearsofeducation.2781.98.0481.60.109Unitsofalcoholperweek.019.59.553Smoker(yes/no).25.804Blockthree:Cognitiveabilityage11years.1295.29(1,425)=28.0,.001RPM=RavensProgressiveMatrices.V.J.Bourneetal./PersonalityandIndividualDierences42(2007)1551 1559 cognitiveability(e.g.,Matthews,Chateld,&Brayne,2006).Itislikelythatasimilarpatternwouldbeidentiedinourdata.Oursamplemaynot,therefore,haveincludedpeopleoflowercognitiveability,whoalsomayexperiencemoreextremelevelsofcognitivedecline.Giventhesepotentiallimitations,itispossiblethatourestimatesoftherelationbetweenchildhoodcognitiveabilityandcognitivedeclineinlaterlifemaythereforebeanunderestimate.Oneparticularstrengthofthispaperisthattherelationshipbetweenchildhoodcognitiveabilityandchangeincognitiveabilityinlaterlifewasfoundevenafteraccountingforthevarianceex-plainedbyfrequentlycitedriskfactorsforcognitiveageing.Whilstweattemptedtocontrolforanumberofpossiblecovariates,therearestillanumberofotherpossiblefactorsthatcouldinu-encecognitivedeclineinlaterlife.AfurtherissuetoconsideriswhethertherelationshipbetweenchildhoodIQandcognitivedeclineinlaterlifeisadirectone,orwhetherchildhoodintelligencemightinuenceotherfactors.Theseincludehealthbehaviours(e.g.,smoking,alcoholconsump-tion,diet),whichmaysubsequentlyimpactoncognitivevariationinlaterlife(Gottfredson,2004Poorphysicalhealthhasalsobeenidentiedasariskfactorforcognitivedecline(vanHoorenetal.,2005).Inconclusion,whilstestimatorsofpriorcognitiveabilitysuchaseducationandoccupationareoftendescribedaspredictorsofcognitivedeclineinlaterlife,ourstudydemon-stratesthatchildhoodcognitiveabilitymakesanimportantadditionalcontributiontocognitiveChristensen,H.,&Henderson,A.S.(1991).Isagekindertotheinitiallymoreable?AstudyofeminentscientistsandPsychologicalMedicine,21,935 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