诊断学概念-课件

PredictiveValuesBobL.Larson,DVM,PhDUniversityofMissouriCommercialAgriculture,BeefFocusTeamPredictiveValuesBobL.Larson1UseandInterpretationofDiagnosticTestsHelptomakeadiagnosis(doesnotstandalone)JudgeseverityofdiseasePredictsubsequentclinicalcourseofdiseaseEstimatelikelyresponsivenesstotherapyDetermineresponsetotherapy(posttherapy)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUseandInterpretationofDiag2DiagnosticTestsMustbetestedagainsta“goldstandard”Althoughnoperfecttestexists,agoldstandardisanaccepted,reliabletestPropertiesofdiagnostictestsSensitivity=

proportionoftruepositivesthattestpositiveHoweffectiveisthetestatidentifyinganimalswiththecondition?Specificity=

proportionoftruenegativesthattestnegativeHoweffectiveisthetestatidentifyinganimalswithoutthecondition?MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsMustbetested3DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus4DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTruePositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus5DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeTrueNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus6DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveFalsePositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus7DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeFalseNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus8DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus9DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus10DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)Falsenegative=c/(a+c)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus11DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)Falsenegative=c/(a+c)Falsepositive=b/(b+d)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus12NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi13NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi14NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi15NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi16NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi17Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementWherecut-offisplaceddeterminessensitivityandspecificityMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr18Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementWherecut-offisplaceddeterminessensitivityandspecificityNormalAbnormalFewFalseNegativesHighSensitivity-result+resultMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr19Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementWherecut-offisplaceddeterminessensitivityandspecificityNormalAbnormalFewFalsePositivesHighSpecificity-result+resultMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr20Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementWherecut-offisplaceddeterminessensitivityandspecificityNormalAbnormalTradeoffbetweenFalse–andFalse+-result+resultMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr21Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementTestwithHighSensitivityNormalAbnormalAnegativeresultallowsyoutorule-outwhateveryouaretesting-result+resultSnNoutMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr22Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementTestwithHighSpecificityNormalAbnormalApositiveresultallowsyoutorule-inwhateveryouaretesting-result+resultSpPinMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnostictestsuseanarbitr23DiagnosticTestsSensitivityandspecificityareinverselyrelatedSensitivityandspecificityarepropertiesofthediagnostictestandtellusifthetestisvalidTestsensitivityandspecificityhavelittleeffectontheconfidenceaveterinarianhasinanindividualresult.MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsSensitivityan24Because…NumberMeasurementMyillustrationisnotconsistentwithtruediseasedynamicsinapopulation(therealworld)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsBecause…NumberMeasurementMy25NumberMeasurementBecause…Myillustrationisnotconsistentwithtruediseasedynamicsinapopulation(therealworld)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberMeasurementBecause…Myi26PredictiveValue

WhatwearereallyinterestedinPredictivevaluestellusifatestisusefulPositivePredictiveValue(PPV)TheprobabilitythatananimalwithapositivetestresultistrulypositiveNegativePredictiveValue(NPV)TheprobabilitythatananimalwithanegativetestresultistrulynegativeDependentondiseaseprevalenceandtestsensitivityandspecificityMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPredictiveValue

Whatwearer27PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000Prevalenceis90%(900/1000=90%)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb28PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000TestSensitivity=540/900=60%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb29PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000TestSensitivity=60%NPV=90/450=20%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb30PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000TestSensitivity=60%NPV=90/450=20%TestSpecificity=90/100=90%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb31PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000TestSensitivity=60%NPV=90/450=20%TestSpecificity=90%PPV=540/550=98%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb32PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearolddairycow,withtypicalhistory,clinicalsignsandpositiveherd-matesWeassume90%ofcowswiththisdescriptionarepositive(prevalence=90%)Dz+Dz-TestPositive54010550TestNegative360904509001001,000PPV=540/550=98%NPV=90/450=20%Withpositivetestweare98%suresheisatruepositiveWithnegativetestweare20%suresheisatruenegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb33PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000Prevalenceis50%(500/1000=50%)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb34PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000TestSensitivity=300/500=60%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb35PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000TestSensitivity=60%NPV=450/650=69%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb36PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000TestSensitivity=60%NPV=450/650=69%TestSpecificity=450/500=90%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb37PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000TestSensitivity=60%NPV=450/650=69%TestSpecificity=90%PPV=300/350=86%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb38PPVandNPVAssumeatestforbovineJohne’sis60%sensitiveand90%specificOnexaminationofa5yearoldbeefcow,withtypicalhistory,clinicalsignsandunknownherdstatusWeassume50%ofcowswiththisdescriptionarepositive(prevalence=50%)Dz+Dz-TestPositive30050350TestNegative2004506505005001,000PPV=300/350=86%NPV=450/650=69%Withpositivetestweare86%suresheisatruepositiveWithnegativetestweare69%suresheisatruenegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVAssumeatestforb39PredictiveValueofaDiagnosticTest

PPVandNPVPPVandNPVaregreatlyinfluencedbypre-testlikelihoodofdiseasePublishedprevalencedataYourclinicalskillsandjudgmentPositive%Negative%PrePostPrePostExample190981020Example250865069MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPredictiveValueofaDiagnost40PPVandNPVTheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood:96%sensitiveand99%specificHowever,theprevalenceofPIanimalsinthegeneralcalfpopulationislow(0.3%)So,howdoesaverygoodtestperforminapopulationwithlowprevalence?MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTheimmunohistochem41PPVandNPVTheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood:96%sensitiveand99%specificHowever,theprevalenceofPIanimalsinthegeneralcalfpopulationislow(0.3%)So,howdoesaverygoodtestperforminapopulationwithlowprevalence?BVDPIDz+Dz-TestPositive2889971,285TestNegative1298,70398,71530099,700100,000TestSensitivity=96%TestSpecificity=99%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTheimmunohistochem42PPVandNPVTheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood:96%sensitiveand99%specificHowever,theprevalenceofPIanimalsinthegeneralcalfpopulationislow(0.3%)So,howdoesaverygoodtestperforminapopulationwithlowprevalence?BVDPIDz+Dz-TestPositive2889971,285TestNegative1298,70398,71530099,700100,000TestSensitivity=96%NPV=98,703/98,715=99.9%TestSpecificity=99%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTheimmunohistochem43PPVandNPVTheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood:96%sensitiveand99%specificHowever,theprevalenceofPIanimalsinthegeneralcalfpopulationislow(0.3%)So,howdoesaverygoodtestperforminapopulationwithlowprevalence?BVDPIDz+Dz-TestPositive288True+997False+1,285TestNegative1298,70398,71530099,700100,000TestSensitivity=96%NPV=98,703/98,715=99.9%TestSpecificity=99%PPV=288/1,285=22%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTheimmunohistochem44PPVandNPVTheimmunohistochemistrytestforpersistentlyinfectedBVDanimalsisverygood:96%sensitiveand99%specificHowever,theprevalenceofPIanimalsinthegeneralcalfpopulationislow(0.3%)So,howdoesaverygoodtestperforminapopulationwithlowprevalence?BVDPIDz+Dz-TestPositive2889971,285TestNegative1298,70398,71530099,700100,000TestSensitivity=96%NPV=98,703/98,715=99.9%TestSpecificity=99%PPV=288/1,285=22%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTheimmunohistochem45PPVandNPVDisease+Population=100headDisease-Population99%SpecificPPVandNPVDisease+Populatio46PPVandNPVEvaluatingacomponentofthephysicalexaminationObservationforpresentofdyspneaAuscultationwithstethoscopeEtc.Preg.Preg+Preg-TestPositive9022904TestNegative484896950501000TestSensitivity=95%TestSpecificity=96%PregnancyDeterminationviaRectalPalpationAssumehighsensitivityandspecificity(truth?)Prevalenceis95%PPV=99.8%NPV=50%MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVEvaluatingacompon47PPVandNPVTakeHomeAsprevalencefalls,PPV(positivepredictivevalue)mustalsofallandNPV(negativepredictive)valuemustrise,regardlessofsensitivityandspecificityofthetest.Asprevalenceincreases,PPVmustincreaseandNPVmustfall,regardlessofthesensitivityandspecificityofthetest.Yourclinicaljudgmentoftensetsthepre-testprobability(prevalence)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsPPVandNPVTakeHomeAspreval48DiagnosticTestingStrategyMustknowwhatyouareaskingRuling-outapreliminarydiagnosisRuling-inapreliminarydiagnosisScreeningforregulatoryorbiosecurityreasonsDescribingaherdproductionsituationMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestingStrategyMus49DiagnosticTestingStrategyMustunderstandpredictivevalueoftestinthepopulationyouaretestingMustknowwhatyouareaskingRuling-outapreliminarydiagnosisRuling-inapreliminarydiagnosisScreeningforregulatoryorbiosecurityreasonsDescribingaherdproductionsituationMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestingStrategyMus50DiagnosticTestingStrategyMaywanttousemorethanonediagnostictestMustunderstandpredictivevalueoftestinthepopulationyouaretestingMustknowwhatyouareaskingRuling-outapreliminarydiagnosisRuling-inapreliminarydiagnosisScreeningforregulatoryorbiosecurityreasonsDescribingaherdproductionsituationMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestingStrategyMay51UsingmorethanonediagnostictestSeries

/ConfirmatoryRuntwoormoretestssequentiallyUsedtoconfirmapositivetestwithalowpositivepredictivevalue(lowspecificityorlowprevalence)AnegativeresultineitherresultsinanegativeconclusionMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUsingmorethanonediagnostic52UsingmorethanonediagnostictestSeries/ConfirmatoryRuntwoormoretestssequentiallyUsedtoconfirmapositivetestwithalowpositivepredictivevalue(lowspecificityorlowprevalence)AnegativeresultineitherresultsinanegativeconclusionParallelRuntwoormoretestsconcurrentlyUsedtofindpositivecaseswhenthetesthasalownegativepredictivevalue(lowsensitivityorhighprevalence)ApositiveresultineitherresultsinapositiveconclusionMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUsingmorethanonediagnostic53UsingmorethanonediagnostictestTestInterpretationFAVISeriesParallel-+-+--++MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUsingmorethanonediagnostic54UsingmorethanonediagnostictestTestInterpretationFAVISeriesParallel-+-+--++Series=Anegativeresultineithertest=negativeinterpretation--(-)+MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUsingmorethanonediagnostic55UsingmorethanonediagnostictestTestInterpretationFAVISeriesParallel-+-+--++Series=Anegativeresultineithertest=negativeinterpretation--(-)+-+++Parallel=Apositiveresultineithertest=positiveinterpretationMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUsingmorethanonediagnostic56诊断学概念-课件57PredictiveValuesBobL.Larson,DVM,PhDUniversityofMissouriCommercialAgriculture,BeefFocusTeamPredictiveValuesBobL.Larson58UseandInterpretationofDiagnosticTestsHelptomakeadiagnosis(doesnotstandalone)JudgeseverityofdiseasePredictsubsequentclinicalcourseofdiseaseEstimatelikelyresponsivenesstotherapyDetermineresponsetotherapy(posttherapy)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsUseandInterpretationofDiag59DiagnosticTestsMustbetestedagainsta“goldstandard”Althoughnoperfecttestexists,agoldstandardisanaccepted,reliabletestPropertiesofdiagnostictestsSensitivity=

proportionoftruepositivesthattestpositiveHoweffectiveisthetestatidentifyinganimalswiththecondition?Specificity=

proportionoftruenegativesthattestnegativeHoweffectiveisthetestatidentifyinganimalswithoutthecondition?MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsMustbetested60DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus61DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTruePositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus62DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeTrueNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus63DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveFalsePositiveTestNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus64DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveTestNegativeFalseNegativeMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus65DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus66DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus67DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)Falsenegative=c/(a+c)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus68DiagnosticTestsDiseaseStatusPresentAbsentTestPositiveaba+bTestNegativecdc+da+cb+da+b+c+dSensitivity=a/(a+c)Specificity=d/(b+d)Falsenegative=c/(a+c)Falsepositive=b/(b+d)MeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsDiagnosticTestsDiseaseStatus69NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi70NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi71NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi72NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi73NumberofanimalsMeasurementDiagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)PopulationAPopulationBMeasurementofdiseaseeventsInfectiousdiseaseepidemiologyInterpretingdiagnostictestsNumberofanimalsMeasurementDi74Diagnostictestsuseanarbitrarycut-offtoseparatetwopopulations(normalvs.abnormal)NumberMeasurementWherecut-offisplaceddeterminessensitivityandspecificityMeasurementofdiseaseeventsInfectiousdis