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Case-controlstudiesCase-controlstudiesThisversionismadeforbilingualteaching.Case-controlstudyisanessentialresearchdesignofEpidemiology,whichinvolvesidentifyingpatientswhohavetheoutcomeofinterest(cases)andcontrolpatientswhodonothavethatsameoutcome,andlookingbacktoseeiftheyhadtheexposureofinterest.Theexposurecouldbesomeenvironmentalfactor,abehaviouralfactor,orexposuretoadrugorothertherapeuticintervention.ThisversioniSelectStudyDesigntoMatchtheResearchGoalsSelectStudyDesigntoMatchtCase-ControlStudiesIntroductionMatchingInvestigateExampleDesignofCase-ControlStudiesDatacollectionandanalysisBiasStrengthsandWeaknessesSeveralimportantfeaturesCase-ControlStudiesIntroductiIntroductionHistoricalPerspectiveDefinitionTypesofDesignIntroductionHistoricalPerspecUniquecontributionofepidemiologytotherepertoireofclinicalresearchdesignsFirstcase-controlstudyperformedinlate1950sDollandHill’sstudyoflungcancerandsmokingbehavioramongphysiciansJeromeCornfield’sclassicdescriptionof“RetrospectiveStudies”Newstatisticaltoolsweredevelopedtoanalyzethestudydesign-logisticregressionHistoricalPerspectiveIntroductionUniquecontributionofepidemiDefinition

Acase-controlstudyisadesigninwhichindividualswithaneventorconditionofinterest,CASES,areidentifiedandthencomparedwithregardtooneormoreexposurestoindividualswithouttheeventorconditionofinterest,CONTROLS.Case-controlinvestigationstypicallyaredesignedtoassesstheassociationbetweenoccurrenceofdiseaseandanexposuresuspectedofcausing(orpreventing)thatdisease.IntroductionDefinition Acase-controlabcdCasesControlsDirectionofinquiryExposedExposedUnexposedUnexposeda/(a+c)b/(b+d)IntroductionabcdCasesControlsDirectionoTypesFamilyofepidemiologicalstudydesignsTraditionalcase-controldesignCase-controlstudieswithincohortsNestedcase-controlstudydesignCase-cohortstudydesignCase-parentstudydesignCase-onlystudydesignIntroductionTypesFamilyofepidemiologicalMatchingSummarizeTypesProblemswithMatchingMatchingSummarize

MatchingisdefinedastheprocessofselectingcontrolssothattheyresemblethecaseswithregardtocertaincharacteristicsThegoalofmatchingistocreatesimilardistributionsbetweencasesandcontrolswithregardtocertaincharacteristicsMatchingcanbeusedtoAdjustforpotentialconfoundingfactorsIncreaseprecisionofestimateMatchingSummarize

MatchingisdefinedastheprIndividuallevelmatchingForeachcaseinthestudy,oneormorecontrolsareselectedwithidentical(similar)characteristicsasthecaseFrequency,orgroup,matchingSelectcontrolssothattheproportionwithacertaincharacteristicisidenticaltotheproportionofcaseswiththatcharacteristicMatchingTypesIndividuallevelmatchingMatch

DifficultandexpensiveCannotevaluatetheeffectofcontrolledvariablesMaylimittheabilitytocontrolforothervariablesOvermatchingControlsresemblecasesintermsofknownandunknowncharacteristics,someofwhichmaybeassociatedwiththediseaseProblemswithMatchingMatching

DifficultandexpensiveProbleInvestigateExampletheassociationbetweenoccurrenceofEosinophilia-myalgiasyndrome(EMS)andIngestionofL-tryptophan.BackgroundconductresultsInvestigateExampletheassociaInvestigateExampleBackgroundEMSwasfirstrecognizedinOctober1989,itoccurspredominantlyinwomenandisrelativelyrare.whenastutephysiciansdeterminedthatthreepeoplewithunexplainedmyalgiasandeosinophiliahadconsumedL-tryptophan.Promptresponsebyhealthdepartmentsquicklyledtocase-controlstudies,theresultsofwhichsuggestedthatingestionofL-tryptophanwasthecauseofEMS.InvestigateExampleBackgroundTheCentersforDiseaseControlandPrevention(CDC)conductedaseriesofcase-controlstudiesin1989and1990.OneofthestudiesconductedinMinnesota,Researchersselected63casesubjectsofEMSinthemetropolitanareaofMinneapolis-St.Paul.Researchersrandomlyselected5188controlsubjectsinthesamearea.ResearchersinterviewedsubjectsandaskedabortpotentialriskfactorsandabouttheiruseofL-tryptophan.InvestigateExampleConductTheCentersforDiseaseControL-tryptophanwastakensignificantlymorefrequentlybycasesthanbycontrols—61of63casesubjects(97%),butonly101of5188controlsubjects(2%).L-Tryptophan-containingproductsweretakenoffthemarketinNovember1989,In1990,aftertherecallofL-tryptophan,thenumberofreportedcasesfelltonearzero.InvestigateExampleResultsL-tryptophanwastakensignifiDesignSelectionofCasesDevelopacasedefinitionthenidentifynewcaseswithinaspecifiedtimeperiodSelectionofControlsThesampleofcontrolsshouldhavethesameprevalenceofexposureasthesourcepopulationofunaffectedpersons.DeterminationofExposureDesignSelectionofCasesSelectionofCasesDesignSourcesofcasesSpeciesofcasesSomethingimportantSelectionofCasesDesignSoSelectionofCases

SourcesofCasesSourcesofCasesHospitalorclinicBecauseriskfactorsmayresultfromreferralpatternstospecifichospitals,multiplehospitals/clinicsoftenchosenReferralofmoreillpatientstohospitals,especiallytertiarycarecentersPopulation-basedorcommunityNewcasesreportedtohealthdepartments,registries,hospitalrecorddepartments,etc.CasescannotbeselectedbasedonknownorunknownassociationwithexposureofinterestDesignSelectionofCasesSelectionofCases

SpeciesofCasesNewlydiagnosedorincidentcasesPreviouslyexistingorprevalentcasesIncidentcasespreferredoverprevalentcasesinmostsettingsIfprevalentcaseschosen,thenriskfactorsidentifiedfordiseasemaybethoserelatedmoretosurvivalwithdiseasethandiseaseoccurrence.Survivorshipbiasalsotrueforincidentcases,butminimizedDesignSelectionofCases

SpSpecifythedefinitionofacaseThecriteriashouldminimizethelikelihoodthatanaffectedperson(truecase)ismissed(i.e,thecriteriamustbesensitive).Anonaffectedpersonisfalselyclassifiedasacase(i.e,thecriteriamustbespecific).Design

SelectionofCases

SomethingImportantSpecifythedefinitionofacaSelectionofControlsSourcesofcontrolsMultiplecontrolsSomethingimportantDesignSelectionofControlsSourcesoHospitalcontrolgroup

Hospitalizedpatients,bestifchosenfromthesamehospitalascasesinordertocontrolforunknownreferencepopulationSelectfromallpatientsadmittedtothehospitalSelectfromspecificdiagnosisDesignSelectionofControls

SourcesofControls(1)HospitalcontrolgroupDesignSSelectionofControls

SourcesofControls(2)CommunitycontrolgroupProbabilitysamplebest,butnotoftenpracticalSelectfromschoolrosters,insurancecompanies,etc.NeighborsofcasesRandomdigitdialingBestfriendDesignSelectionofControlsSelectionofControls

MultipleControlsControlsofthesametypeMayimproveprecisionofthemeasureofassociationPrecisionrarelyimprovedwithmorethan5controlspercaseControlsofdifferenttypesHospitalcontrolsandcommunitycontrolspercaseDesignSelectionofControlsControlscannotbeselectedbasedonknownorunknownassociationwithexposure(s)orriskfactorsofinterestDesignSelectionofControls

SomethingImportantControlscannotbeselectedba

DeterminationofExposureExposureSomethingimportantDesign

DeterminationofExposureExpo

DeterminationofExposure

ExposureExposureisdeterminedina‘retrospective’manner,thatisonemustlookbackintimetoassessexposurestatusbeforeapersonbecameacase.Eachindividual’spriorexposuretotheriskfactorofinterestOtherexposuresDesign

DeterminationofExposure

DeterminationofExposure

SomethingImportant(1)CasesandcontrolsmustbeassessedforexposureinthesamewayInterviewsshouldbestandardized,monitored,andconductedbytrainedinterviewers.Design

DeterminationofExposure

ExposuremustbemeasuredinablindedmannerDatacollectorsmustbeunawareofwhethersubjectisacaseorcontrolDatacollectorsshouldbeunawareofthestudyhypothesisDesign

DeterminationofExposure

SomethingImportant(2)ExposuremustbemeasuredinaDatacollectionandanalysisCollectionofDataAnalysisofDataORUnmatchedanalysisMatchedanalysisAnalyticStrategyDatacollectionandanalysisCo

CollectionofDataInterviewsandquestionnairesInformationconcerningriskfactorsmayalsobeobtainedfrommedical,occupational,orotherrecords.Datacollectionandanalysis

CollectionofDataInterviews

AnalysisofDataDatacollectionandanalysisUnexposed-cExposed-aPopulationatRiskExposed-bCases

ControlsUnexposed-d

AnalysisofDataDatacollect

OddsRatioThepowerofthestudydesignliesinthesymmetryoftheOR.ORistheoddsofexposuregivendiseasedividedbytheoddsofexposuregivennodisease.Rememberthattheoddsofexposureamongcasescomparedwithcontrolsisthesameastheoddsofdiseaseamongexposedandunexposed.a+b+c+d

OddsRatioThepoweroftheExposedUnexposedTotalCasesControlsacbda+bc+dTotala+cb+da+b+c+dUnmatchedanalysis

DatacollectionandanalysisExposedUnexposedTotalCasesaba+Unmatchedanalysis

UnmatchedanalysisControlExposedControlUnexposedTotalCaseexposedaba+bCaseunexposedcdc+dTotala+cb+da+b+c+d

Case-controlpairsthatsharethesameexposurestatusdonotcontributetotheestimateofrisk.DatacollectionandanalysisMatchedanalysisControlExposedControlUnexposMatchedanalysisDatacollectionandanalysisMatchedanalysisDatacollectio

AnalyticStrategyAssessrelationship/associationbetweenExposureandindependentvariablesCase/ControlstatusandindependentvariablesCalculatecrude,orunadjusted,ORforexposure-caseassociationMatchedanalysisrequiredformatchedstudiesDatacollectionandanalysis

AnalyticStrategyAssessrelat

AnalyticStrategyStratifiedanalysisCalculatestratum-specificORsforexposure-caserelationshipDeterminepresenceofconfoundingandinteractionLogisticregressionanalysisRegressiontechniqueusedtoadjustforconfoundingandinteractionSpeciallogisticmodelappliedinmatchedstudiesDatacollectionandanalysis

AnalyticStrategyStratifiedaBiasIntroductionSelectionbiasInformationbiasConfoundingBiasIntroduction

IntroductionCase-controlstudiesaresubjecttobiasandconfounding,bothwilldistorttheresultsofthestudyBiasisdefinedasthedeviationofresults,orinferences,fromthetruth,orprocessesleadingtosuchdeviation.Thereareabout75differenttypesofbiasnowidentifiedinpublishedcase-controlstudiesBias

IntroductionCase-controlstudSelectionBiasFeaturesTypesBiasSelectionBiasFeaturesBiasFeatures(1)Selectionbiasreflectssystematicerrorsthatarisefromthewayinwhichsubjectsareselected.Ifthepriorexposureofthecasesstudieddiffersfromthatofallcasesarisingfromthesourcepopulation—orifpriorexposureofcontrolsdiffersfromthatofpersonsinthesourcepopulationwithoutthediseaseorinterest—selectionbiasmaybepresent.BiasFeatures(1)SelectionbiasrefFeatures(2)Preferentialdiagnosisofexposedcasesmayleadtoselectionbias.Lowparticipationmayleadtoselectionbias.Errorsinsamplingcontrolsfromthesourcepopulationcanalsocreateselectionbias.BiasFeatures(2)PreferentialdiagnTypesAdmissionratebiasPrevalence-incidencebiasDetectionsignalbiasTimeeffectbiasBiasTypesAdmissionratebiasBiasInformationBiasAdistortioninmeasuringexposureoroutcomedatathatresultsindifferentquality(i.e.,accuracyorreliability)orfrequencyofinformationbetweencomparisongroups.RecallbiasConfoumdingbiasBiasInformationBiasAdistortioniConfoundingBiasConfoundingisadistortionofresultsthatoccurswhentheapparenteffectsoftheexposureofinterestareattributableentirelyorinparttotheeffectsofanextraneousvariable.CriteriaforconfoundingFactorisassociatedwithexposureFactorisassociatedwithdiseaseintheabsenceofexposureFactorisnotinthecausalpathbetweenexposureandoutcomeBiasConfoundingBiasConfoundingis

StrengthsandWeaknessesStrengthsRarediseaseLonglatencybetweenexposureanddiseaseExploremultiplehypothesesInexpensive

StrengthsandWeaknessesStren

StrengthsandWeaknessesWeaknessesPronetobiasTemporalrelationshipscannotbeestablishedInefficientforrareexposures,unlessexposureoftenleadtodisease

StrengthsandWeaknessesWeakn

SeveralimportantfeaturesThestudyprovidesanefficientmeanstostudyrarediseases.Case-controlstudiestendtobemorefeasiblethanotherstudies.Case-controlstudiesallowresearcherstoinvestigateseveralriskfactors.Asinglecase-controlinvestigationdoesnot“prove”causality,butitcanprovidesuggestiveevidenceofacausalrelationshipthatwarrantsinterventionbypublichealthofficialstoreduceexposuretotheimplicatedriskfactor.

SeveralimportantfeaturesThCase-controlstudiesCase-controlstudiesThisversionismadeforbilingualteaching.Case-controlstudyisanessentialresearchdesignofEpidemiology,whichinvolvesidentifyingpatientswhohavetheoutcomeofinterest(cases)andcontrolpatientswhodonothavethatsameoutcome,andlookingbacktoseeiftheyhadtheexposureofinterest.Theexposurecouldbesomeenvironmentalfactor,abehaviouralfactor,orexposuretoadrugorothertherapeuticintervention.ThisversioniSelectStudyDesigntoMatchtheResearchGoalsSelectStudyDesigntoMatchtCase-ControlStudiesIntroductionMatchingInvestigateExampleDesignofCase-ControlStudiesDatacollectionandanalysisBiasStrengthsandWeaknessesSeveralimportantfeaturesCase-ControlStudiesIntroductiIntroductionHistoricalPerspectiveDefinitionTypesofDesignIntroductionHistoricalPerspecUniquecontributionofepidemiologytotherepertoireofclinicalresearchdesignsFirstcase-controlstudyperformedinlate1950sDollandHill’sstudyoflungcancerandsmokingbehavioramongphysiciansJeromeCornfield’sclassicdescriptionof“RetrospectiveStudies”Newstatisticaltoolsweredevelopedtoanalyzethestudydesign-logisticregressionHistoricalPerspectiveIntroductionUniquecontributionofepidemiDefinition

Acase-controlstudyisadesigninwhichindividualswithaneventorconditionofinterest,CASES,areidentifiedandthencomparedwithregardtooneormoreexposurestoindividualswithouttheeventorconditionofinterest,CONTROLS.Case-controlinvestigationstypicallyaredesignedtoassesstheassociationbetweenoccurrenceofdiseaseandanexposuresuspectedofcausing(orpreventing)thatdisease.IntroductionDefinition Acase-controlabcdCasesControlsDirectionofinquiryExposedExposedUnexposedUnexposeda/(a+c)b/(b+d)IntroductionabcdCasesControlsDirectionoTypesFamilyofepidemiologicalstudydesignsTraditionalcase-controldesignCase-controlstudieswithincohortsNestedcase-controlstudydesignCase-cohortstudydesignCase-parentstudydesignCase-onlystudydesignIntroductionTypesFamilyofepidemiologicalMatchingSummarizeTypesProblemswithMatchingMatchingSummarize

MatchingisdefinedastheprocessofselectingcontrolssothattheyresemblethecaseswithregardtocertaincharacteristicsThegoalofmatchingistocreatesimilardistributionsbetweencasesandcontrolswithregardtocertaincharacteristicsMatchingcanbeusedtoAdjustforpotentialconfoundingfactorsIncreaseprecisionofestimateMatchingSummarize

MatchingisdefinedastheprIndividuallevelmatchingForeachcaseinthestudy,oneormorecontrolsareselectedwithidentical(similar)characteristicsasthecaseFrequency,orgroup,matchingSelectcontrolssothattheproportionwithacertaincharacteristicisidenticaltotheproportionofcaseswiththatcharacteristicMatchingTypesIndividuallevelmatchingMatch

DifficultandexpensiveCannotevaluatetheeffectofcontrolledvariablesMaylimittheabilitytocontrolforothervariablesOvermatchingControlsresemblecasesintermsofknownandunknowncharacteristics,someofwhichmaybeassociatedwiththediseaseProblemswithMatchingMatching

DifficultandexpensiveProbleInvestigateExampletheassociationbetweenoccurrenceofEosinophilia-myalgiasyndrome(EMS)andIngestionofL-tryptophan.BackgroundconductresultsInvestigateExampletheassociaInvestigateExampleBackgroundEMSwasfirstrecognizedinOctober1989,itoccurspredominantlyinwomenandisrelativelyrare.whenastutephysiciansdeterminedthatthreepeoplewithunexplainedmyalgiasandeosinophiliahadconsumedL-tryptophan.Promptresponsebyhealthdepartmentsquicklyledtocase-controlstudies,theresultsofwhichsuggestedthatingestionofL-tryptophanwasthecauseofEMS.InvestigateExampleBackgroundTheCentersforDiseaseControlandPrevention(CDC)conductedaseriesofcase-controlstudiesin1989and1990.OneofthestudiesconductedinMinnesota,Researchersselected63casesubjectsofEMSinthemetropolitanareaofMinneapolis-St.Paul.Researchersrandomlyselected5188controlsubjectsinthesamearea.ResearchersinterviewedsubjectsandaskedabortpotentialriskfactorsandabouttheiruseofL-tryptophan.InvestigateExampleConductTheCentersforDiseaseControL-tryptophanwastakensignificantlymorefrequentlybycasesthanbycontrols—61of63casesubjects(97%),butonly101of5188controlsubjects(2%).L-Tryptophan-containingproductsweretakenoffthemarketinNovember1989,In1990,aftertherecallofL-tryptophan,thenumberofreportedcasesfelltonearzero.InvestigateExampleResultsL-tryptophanwastakensignifiDesignSelectionofCasesDevelopacasedefinitionthenidentifynewcaseswithinaspecifiedtimeperiodSelectionofControlsThesampleofcontrolsshouldhavethesameprevalenceofexposureasthesourcepopulationofunaffectedpersons.DeterminationofExposureDesignSelectionofCasesSelectionofCasesDesignSourcesofcasesSpeciesofcasesSomethingimportantSelectionofCasesDesignSoSelectionofCases

SourcesofCasesSourcesofCasesHospitalorclinicBecauseriskfactorsmayresultfromreferralpatternstospecifichospitals,multiplehospitals/clinicsoftenchosenReferralofmoreillpatientstohospitals,especiallytertiarycarecentersPopulation-basedorcommunityNewcasesreportedtohealthdepartments,registries,hospitalrecorddepartments,etc.CasescannotbeselectedbasedonknownorunknownassociationwithexposureofinterestDesignSelectionofCasesSelectionofCases

SpeciesofCasesNewlydiagnosedorincidentcasesPreviouslyexistingorprevalentcasesIncidentcasespreferredoverprevalentcasesinmostsettingsIfprevalentcaseschosen,thenriskfactorsidentifiedfordiseasemaybethoserelatedmoretosurvivalwithdiseasethandiseaseoccurrence.Survivorshipbiasalsotrueforincidentcases,butminimizedDesignSelectionofCases

SpSpecifythedefinitionofacaseThecriteriashouldminimizethelikelihoodthatanaffectedperson(truecase)ismissed(i.e,thecriteriamustbesensitive).Anonaffectedpersonisfalselyclassifiedasacase(i.e,thecriteriamustbespecific).Design

SelectionofCases

SomethingImportantSpecifythedefinitionofacaSelectionofControlsSourcesofcontrolsMultiplecontrolsSomethingimportantDesignSelectionofControlsSourcesoHospitalcontrolgroup

Hospitalizedpatients,bestifchosenfromthesamehospitalascasesinordertocontrolforunknownreferencepopulationSelectfromallpatientsadmittedtothehospitalSelectfromspecificdiagnosisDesignSelectionofControls

SourcesofControls(1)HospitalcontrolgroupDesignSSelectionofControls

SourcesofControls(2)CommunitycontrolgroupProbabilitysamplebest,butnotoftenpracticalSelectfromschoolrosters,insurancecompanies,etc.NeighborsofcasesRandomdigitdialingBestfriendDesignSelectionofControlsSelectionofControls

MultipleControlsControlsofthesametypeMayimproveprecisionofthemeasureofassociationPrecisionrarelyimprovedwithmorethan5controlspercaseControlsofdifferenttypesHospitalcontrolsandcommunitycontrolspercaseDesignSelectionofControlsControlscannotbeselectedbasedonknownorunknownassociationwithexposure(s)orriskfactorsofinterestDesignSelectionofControls

SomethingImportantControlscannotbeselectedba

DeterminationofExposureExposureSomethingimportantDesign

DeterminationofExposureExpo

DeterminationofExposure

ExposureExposureisdeterminedina‘retrospective’manner,thatisonemustlookbackintimetoassessexposurestatusbeforeapersonbecameacase.Eachindividual’spriorexposuretotheriskfactorofinterestOtherexposuresDesign

DeterminationofExposure

DeterminationofExposure

SomethingImportant(1)CasesandcontrolsmustbeassessedforexposureinthesamewayInterviewsshouldbestandardized,monitored,andconductedbytrainedinterviewers.Design

DeterminationofExposure

ExposuremustbemeasuredinablindedmannerDatacollectorsmustbeunawareofwhethersubjectisacaseorcontrolDatacollectorsshouldbeunawareofthestudyhypothesisDesign

DeterminationofExposure

SomethingImportant(2)ExposuremustbemeasuredinaDatacollectionandanalysisCollectionofDataAnalysisofDataORUnmatchedanalysisMatchedanalysisAnalyticStrategyDatacollectionandanalysisCo

CollectionofDataInterviewsandquestionnairesInformationconcerningriskfactorsmayalsobeobtainedfrommedical,occupational,orotherrecords.Datacollectionandanalysis

CollectionofDataInterviews

AnalysisofDataDatacollectionandanalysisUnexposed-cExposed-aPopulationatRiskExposed-bCases

ControlsUnexposed-d

AnalysisofDataDatacollect

OddsRatioThepowerofthestudydesignliesinthesymmetryoftheOR.ORistheoddsofexposuregivendiseasedividedbytheoddsofexposuregivennodisease.Rememberthattheoddsofexposureamongcasescomparedwithcontrolsisthesameastheoddsofdiseaseamongexposedandunexposed.a+b+c+d

OddsRatioThepoweroftheExposedUnexposedTotalCasesControlsacbda+bc+dTotala+cb+da+b+c+dUnmatchedanalysis

DatacollectionandanalysisExposedUnexposedTotalCasesaba+Unmatchedanalysis

UnmatchedanalysisControlExposedControlUnexposedTotalCaseexposedaba+bCaseunexposedcdc+dTotala+cb+da+b+c+d

Case-controlpairsthatsharethesameexposurestatusdonotcontributetotheestimateofrisk.DatacollectionandanalysisMatchedanalysisControlExposedControlUnexposMatchedanalysisDatacollectionandanalysisMatchedanalysisDatacollectio

AnalyticStrategyAssessrelationship/associationbetweenExposureandindependentvariablesCase/ControlstatusandindependentvariablesCalculatecrude,orunadjusted,ORforexposure-caseassociationMatchedanalysisrequiredformatchedstudiesDatacollectionandanalysis

AnalyticStrategyAssessrelat

AnalyticStrategyStratifiedanalysisCalculatestratum-specificORsforexposure-caserelationshipDeterminepresenceofconfoundingandinteractionLogisticregressionanalysisRegressiontechniqueusedtoadjustforconfoundingandinteractionSpeciallogisticmodelappliedinmatchedstudiesDatacollectionandanalysis

AnalyticStrategyStratifiedaBiasIntroductionSelectionbiasInformationbias

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