the r book survival analysis

《the r book survival analysis》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。

1、25MultivariateStatisticsThisclassofstatisticalmethodsisfundamentallydifferentfromtheothersinthisbookbecausethereisnoresponsevariable.Insteadoftryingtounderstandvariationinaresponsevariableintermsofexplanatoryvariables,inmultivariatestatisticswelookforstructureinthedata.Theproblemistha

2、tstructureisrathereasytofind,andalltoooftenitisafeatureofthatparticulardatasetalone.Therealchallengeistofindgeneralstructurethatwillapplytootherdatasetsaswell.Unfortunately,thereisnoguaranteedmeansofdetectingpattern,andagreatdealofingenuityhasbeenshownbystatisticiansindevisingmeansofpat

3、ternrecognitioninmultivariatedatasets.Themaindivisionisbetweenmethodsthatassumeagivenstructureandseektodividethecasesintogroups,andmethodsthatseektodiscoverstructurefrominspectionofthedataframe.Thereallyimportantpointisthatyouneedtoknowexactlywhatthequestionisthatyouaretryingtoanswer.

4、Donotmistaketheopaquefortheprofound.ThemultivariatetechniquesimplementedinRinclude:
principalcomponentsanalysis(prcomp);
factoranalysis(factanal);
clusteranalysis(hclust,kmeans);
discriminantanalysis(lda,qda);
neuralnetworks(nnet).Thesetechniquesarenotrecommendedunlessyouknowexactlywh

5、atyouaredoing,andexactlywhyyouaredoingit.Beginnersaresometimesattractedtomultivariatetechniquesbecauseofthecomplexityoftheoutputstheyproduce.25.1PrincipalcomponentsanalysisTheideaofprincipalcomponentsanalysis(PCA)istofindasmallnumberoflinearcombinationsofthevariablessoastocapturemostof

6、thevariationinthedataframeasawhole.Withalargenumberofvariablesitmaybeeasiertoconsiderasmallnumberofcombinationsoftheoriginaldataratherthantheentiredataframe.TheRBook,SecondEdition.MichaelJ.Crawley.©2013JohnWiley&Sons,Ltd.Published2013byJohnWiley&Sons,Ltd.810THERBOOKSuppose,forexample,

7、thatyouhadthreevariablesmeasuredoneachsubject,andyouwantedtodistiltheessenceofeachindividual’sperformanceintoasinglenumber.Anobvioussolutionisthearithmeticmeanofthethreenumbers1v+1v+1v,wherevvandvarethethreevariables(e.g.pupils’examscores3132331,23inmaths,physicsandchemistry).Thevecto

8、rofco