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BiostatisticsMain21-30Q21Inalargepopulationwithlittlemigration,theincidenceofdiabetesmellitusrtypellisequalto3casesper1,000peryear;andhasbeenstableforthelast30years.Theprevalenceofthisdiseaseincreasedprogressivelyoverthesameperiod.Whichofthefollowingcouldbethemostlikelyexplanationofthistrendovertime?A.HighmortalityindiabeticsB.SelectivesurvivalC.ImprovedqualityofcareD.DecreasedhospitalizationrateE.IncreaseddiagnosticaccuracyA21Correctanswer:CIncidenceandprevalencearetwoImportantconceptsinepidemiology.Itisthusveryimportanttoknowthedifferencebetweenthesetwo.Incidenceisthemeasureoftheappearanceofnewcases.Prevalenceisthemeasureofthosewiththediseaseinthepopulationataparticularpointintime.Therelationshipbetweenthesetwocategoriescanbedemonstratedbythefollowingapproximationinastablepopulation(littlemigration):Prevalence=(Incidence)x(Time)Theabovevignettedescribedadiseasewitharisingprevalencebutstableincidence.Morepeoplearebeingdocumentedtohavethedisease,whilethenumberofpeoplebeingdiagnosedremainsthesame.Suchtrendcanbeattributedtofactorswhichprolongthedurationofthedisease(e.g.fimprovedqualityofcare).(ChoiceA)Ahighmortalityrateindiabeticswouldresultinadecreasedprevalence.(ChoicesBandD)Selectivesurvivalanddecreasedhospitalizationratearenothelpfulinexplainingtheincreasedprevalencedescribedinthisscenario.(ChoiceE)Increaseddiagnosticaccuracyaffectsboththeprevalenceandincidenceofadisease.EducationalObjective:AnincreasingprevalenceandstableIncidencecanbeattributedtofactorswhichprolongthedurationofadisease(e.g.,improvedqualityofcare-thisscenarioistypicalfortheUSMLE).Q22Bleedingriskisthemajorconcernwhenanticoagulatingpatientswithnon-valvularatrialfibrillation.TheadvertisementpromotesKalaxinasasafemedication.InthestudycomparingKalaxinandwarfarin,whichofthefollowingspecificbleedingrisksweremostsimilarbetweenthe2groups?A.GastrointestinalbleedingB.IntracranialbleedingC.Life-threateningbleedingD.MajorbleedingE.TotalbleedingA22Correctanswer:DThedrugadvertisementiscomparingtheeffectofKalaxinversuswarfarinforpreventingstrokeinnon-valvularatrialfibrillation.Itcomparesthehazardratesforadverseeventsforbothdrugsintheformofhazardratios.Ahazardrateisthechanceofaneventoccurringinoneofthestudygroupsduringasetperiod.Ahazardratioisthechanceofaneventoccurringinthetreatmentgroupcomparedtothechanceofthateventoccurringinthecontrolgroupduringasetperiod.Ahazardratio1indicatesthataneventismorelikelytooccurinthecontrolgroup.Ahazardratio1signifiesthataneventismorelikelytooccurinthetreatmentgroup.Aratiocloseto1implieslittledifferencebetweenthe2groups.Inthisstudy,thehazardratioformajorbleedingwas0.9G;whichistheclosestto1comparedtotheotheransweroptions.Inaddition,the95%confidenceinterval(0.84-1.10)containsthenullvalueof1，indicatingthatthereisnosignificantdifferenceintheriskofmajorbleedingbetweenthe2groups.Thisinformationispresentedinthetextbelowthebargraph.Aswithanycommercialentity,drugmanufacturersmayhaveincentivetomaximizethevisibilityofadrug'sbenefitsoveritsrisksorsideeffects.Asaresult,itisimportanttocriticallyreadallpresentedinformationwhenreviewingadrugadvertisement.(ChoiceA)Thehazardratioforgastrointestinalbleedingis1.75,indicatingthatKalaxinhasahigherchanceofcausinggastrointestinalbleedingthanwarfarin.Thehazardratioformajorgastrointestinalbleedingis1.38.(ChoiceB)Thehazardratioforintracranialbleedingis0,39,indicatingthatKalaxinhasalowerchanceofcausingintracranialbleedingthanwarfarin.(ChoiceC)Thehazardratioforlife-threateningbleedingis0.75rindicatingthatKalaxinhasalowerchanceofcausinglife-threateningbleedingthanwarfarin.(ChoiceE)Thehazardratiofortotalbleedingis0.91,indicatingthatKalaxinhasaslightlylowerchanceofcausingoverallbleedingthanwarfarin.Educationalobjective:Hazardratiosareproportionsthatindicatethechanceofaneventoccurringinthetreatmentgroupcomparedtothechanceoftheeventoccurringinthecontrolgroup.Whenreviewingadrugadvertisement,itisimportanttocriticallyreadallthepresentedinformation.Q23Whenassigningpatientstotreatmentandcontrolgroups:properrandomizationisimportanttoavoidtheeffectofextraneousvariablesinthestudyresults.Inthecurrentstudy,whichofthefollowingformsofadditionalinformationwouldhelpmostindeterminingrandomizationsuccess?A.AnnualstrokeratesB.BaselinepatientcharacteristicsC.PatientcompliancechartD.Patientfollow-upratesE.SubgroupanalysistablesA23Correctanswer:BInanyrandomizedclinicalstudy,thegoalofsuccessfulrandomizationistoeliminatebiasintreatmentassignments.Anidealrandomizationprocessminimizesselectionbias,resultsinnear-equaltreatmentandcontrolgroupsizes,andachievesalowprobabilityofhavingconfoundingvariables.Atableofpatientbaselinecharacteristicsforbothtreatmentandcontrolgroupswouldshowifthe2groupsincludedpatientswithsimilarfeaturesandwouldhelpconfirmproperrandomization.(ChoiceA)Annualstrokerateisanendpointofthestudythatmaybeinfluencedbypatientrandomization,butitdoesnotdeterminesuccessofrandomization.(ChoiceC)Patientcompliancechartsindicatehowwellapatienttoleratedthetreatmentandfollowedthetreatmentregimen：butitwouldnotdirectlyindicatet