power and sample size - mgh biostatistics center

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1、SamplesizeandstudydesignBrianHealy,PhDCommentsfromlasttimeWedidnotcoverconfoundingToomuchinoneclass/Notenoughexamples/SuperficiallevelIwantedtoshowoneexampleforeachtypeofanalysissothatyoucandeterminewhatyourdatamatches.Thiswayyoucanspeaktoastatisticianknowingtheb

2、asicideas.MyhopewasforyoutofeelconfidentenoughtolearnmoreaboutthetopicsrelevanttoyouWorkedexamplelecturesThisisnotbasicbiostatisticsIdidTeachforAmericaObjectivesTypeIIerrorHowtoimprovepower?SamplesizecalculationStudydesignconsiderationsReviewPreviousclasseswehave

3、focusedondataanalysisAFTERdatacollectionHypothesistestingallowedustodeterminewhethertherewasastatisticallysignificant:DifferencebetweengroupsAssociationbetweentwocontinuousfactorsAssociationbetweentwodichotomousfactorsExampleWeknowthattheheartrateforhealthyadulti

4、s80beatsperminuteandthishasanapproximatelynormaldistribution(accordingtomywife)Someeliteathletes,likeLanceArmstrong,havelowerheartrate,butitisnotknownifthisistrueonaverageHowcouldweaddressthisquestion?ExperimentaldesignOnewaytodothisistocollectasampleofnormalcont

5、rolsandasampleofeliteathletesandcomparetheirmeanWhattestwouldyouuse?AnotherwayistocollectasampleofeliteathletesandcomparetheirmeantotheknownpopulationmeanThisisaonesampletestNullhypothesis:meanelite=80QuestionHowlargeasampleofeliteathletesshouldIcollect?Whatisthe

6、benefitofhavingalargesamplesize?MoreinformationMoreaccurateestimateofthepopulationmeanWhatisthedisadvantageofalargesamplesize?CostEffortrequiredtocollectWhatisthe“correct”samplesize?EffectofsamplesizeLet’ssaywewantedtoestimatethebloodpressureofpeopleatMGHIfwesamp

7、led3people,wouldwehaveagoodestimateofthepopulationmean?Howmuchwillsamplemeanvaryfromsampletosample?Doesourestimateoftheimproveifwesampled30people?Wouldthesamplemeantovarymoreorlessfromsampletosample?Whatabout300people?Simulationhttp://onlinestatbook.com/stat_sim/

8、sampling_dist/index.htmlWhatistheshapeofthedistributionofsamplemeans?Whereisthecurvecentered?Whathappenstocurveassamplesizeincreases?Technical:Centrallimittheo