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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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