资源描述：
《Imputation missing data》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。
1、CHAPTER25Missing-dataimputationMissingdataariseinalmostallseriousstatisticalanalyses.Inthischapterwediscussavarietyofmethodstohandlemissingdata,includingsomerelativelysimpleapproachesthatcanoftenyieldreasonableresults.WeuseasarunningexampletheSocialIndicatorsSurvey,a
2、telephonesurveyofNewYorkCityfamiliesconductedeverytwoyearsbytheColumbiaUniversitySchoolofSocialWork.Nonresponseinthissurveyisadistractiontoourmaingoalofstudyingtrendsinattitudesandeconomicconditions,andwewouldliketosimplycleanthedatasetsoitcouldbeanalyzedasiftherewer
3、enomissingness.AftersomebackgroundinSections25.1–25.3,wediscussinSections25.4–25.5ourgeneralapproachofrandomimputation.Section25.6discussessituationswherethemissing-dataprocessmustbemodeled(thiscanbedoneinBugs)inordertoperformimputationscorrectly.MissingdatainRandBug
4、sInR,missingvaluesareindicatedbyNA’s.Forexample,toseesomeofthedatafromfiverespondentsinthedatafilefortheSocialIndicatorsSurvey(arbitrarilypickingrows91–95),wetypecbind(sex,race,educ_r,r_age,earnings,police)[91:95,]Rcodeandgetsexraceeduc_rr_ageearningspoliceRoutput[91,]
5、13331NA0[92,]21237135.001[93,]23240NA1[94,]113423.001[95,]131240.00NAInclassicalregression(aswellasmostothermodels),Rautomaticallyexcludesallcasesinwhichanyoftheinputsaremissing;thiscanlimittheamountofinformationavailableintheanalysis,especiallyifthemodelincludesmany
6、inputswithpotentialmissingness.Thisapproachiscalledacomplete-caseanalysis,andwediscusssomeofitsweaknessesbelow.InBugs,missingoutcomesinaregressioncanbehandledeasilybysimplyin-cludingthedatavector,NA’sandall.Bugsexplicitlymodelstheoutcomevariable,andsoitistrivialtouse
7、thismodelto,ineffect,imputemissingvaluesateachiteration.Thingsbecomemoredifficultwhenpredictorshavemissingvalues.Forexample,ifwewantedtomodelattitudestowardthepolice,givenearningsanddemographicpredictors,thenthemodelwouldnotautomaticallyaccountforthemissingvaluesofearni
8、ngs.Wewouldhavetoremovethemissingvalues,imputethem,ormodelthem.InBugs,regressionpredictorsaretypicallyunmodeledandsoBugsdoesnotknow
