class12 Survival Analysis

《class12 Survival Analysis》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、BS805Class12SurvivalAnalysis•SurvivalData–TimestoaneventoPositiveoRightskewedoOftencensored•Kaplan-Meierplotsofsurvivalprobability•TestsofdifferenceinsurvivalpatternbetweengroupsologranktestoGehantest•CoxRegressionSurvivalData•Survivaldatausuallycomefromtrackingthetimeuntilaneventoccurs.•But,maya

2、riseinothersettings,notallofwhicharerelatedtotime.Ingeneral,survivaldatais•Positive(≥0)•Rightskewed(longrighttailonthehistogram,mean>median)•Censored(incompletefollow-uponsomesubjects)Censoringcanhappenbecausethereisnotenoughtimeinthestudyforallsubjectstohaveevents,orifsomesubjectsleavethestudybe

3、foretheyhaveanevent.1BS805Class12ExampleMenwhoexperienceafirstmyocardialinfarction(atypeofheartattack)aregivendailyaspirin,andfolloweduntilasecondmyocardialinfarction(MI)occurs.Subjectsaccrueintothestudyovertime,asthefirstMIisexperienced.•LinebeginswhensubjecthasfirstMI.•Xdenotesasubjectwhohadsec

4、ondMIwhileinstudy.•0denotesasubjectwhodidnothavesecondMIinstudy.•Follow-upisterminatedwhensubjectsleavethestudy,oratstudyend.AspirinTrial0X0XStartEndTimeThetypicalformatforsuchdatawouldbe:obstimetosecondm.i.(yrs)censored12022.513604512BS805Class12Thecensoringcolumnisthecensoringindicator•1iftheob

5、servation’seventwasobserved(happenedwhileonstudy)•0iftheobservationwascensoredBecauseofskewnessandcensoring,meansandstandarddeviationsareeithernotdefined(censoring),ornotveryuseful(skewness).Mediansandinter-quartilerangesarecommonlyusedforsurvivaldata,butifmuchofthedataarecensored,theyalsomaynotb

6、edefined.•ifatleast50%ofdataarecensored,themedianisnotdefined3BS805Class12Kaplan-MeierPlotsProbabilitiesofsurvivingbeyonddifferentvaluesoftimeareusedtodescribesurvivaldata.Subjectswhosurviveattimetarethosewhohavenothadtheeventofinterestinthefirsttunitsoffollow-uptime.Notationfortheprobabilityofsu

7、rvivalattimetisS(t)=Pr(T≥t),whereTisthetimevariable,andS(t)isthesurvivalfunction.Survivalprobabilitiescanbeestimatedwithcensoreddata.•Ifasubjectiscensoredat2years,weknowthathissurvivalisatleastaslongas2years.•Estimates