the scientific model of causality

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1、1THESCIENTIFICMODELOFCAUSALITYJamesJ.Heckman*Causalityisaveryintuitivenotionthatisdifficulttomakeprecisewithoutlapsingintotautology.Twoingredientsarecentraltoanydefinition:(1)asetofpossibleoutcomes(counterfactuals)generatedbyafunctionofasetof‘‘factors’’or‘‘determin

2、ants’’and(2)amanipulationwhereone(ormore)ofthe‘‘factors’’or‘‘determinants’’ischanged.Aneffectisrealizedasachangeintheargumentofastablefunctionthatproducesthesamechangeintheoutcomeforaclassofinterventionsthatchangethe‘‘factors’’bythesameamount.Theoutcomesarecompared

3、atdifferentlevelsofthefactorsorgeneratingvariables.Holdingallfactorssaveoneataconstantlevel,thechangeintheoutcomeassociatedwithmanipulationofthevariedfactoriscalledacausaleffectofthemanipulatedfactor.Thisdefinition,orsomeversionofit,goesbacktoMill(1848)andMarshall(

4、1890).Haavelmo’s(1943)madeitmoreprecisewithinthecontextoflinearequationsmodels.Thephrase‘ceterisparibus’(everythingelseheldconstant)isamainstayofeconomicanalysisThisresearchwassupportedbyNSF97-09-873,00-99195,NSFSES-0241858,NIHR01-HD043411,andtheAmericanBarFoundati

5、on.AnearlierversionofthispaperwaspresentedattheISImeetinginSeoul,Korea,inAugust2001.IamgratefultoJaapAbbringandEdwardVytlacilforveryhelpfuldiscussionsaboutthetopicsofthispaperoverthepastfiveyears.YuXieandespeciallyT.N.Srinivasanmadehelpfulcommentsonthisversion.Some

6、ofthematerialinthispaperalsoappearsinHeckmanandVytlacil(2006a,b).*UniversityofChicago,UniversityCollegeLondon,andtheAmericanBarFoundation2JAMESJ.HECKMANandcapturestheessentialideaunderlyingcausalmodels.Thispaperdevelopsthescientificmodelofcausalitydevelopedineconom

7、icsandcomparesittomethodsadvocatedinepidemiology,statistics,andinmanyofthesocialsciencesoutsideofeconomicsthathavebeeninfluencedbystatisticsandepidemiology.Imaketwomainpointsthatarefirmlyanchoredintheecono-metrictradition.Thefirstisthatcausalityisapropertyofamodelo

8、fhypotheticals.Afullyarticulatedmodelofthephenomenabeing1studiedpreciselydefineshypotheticalorcounterfactualstates.Adefinitionofcausalitydropsout