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EPI 5344: Survival Analysis in Epidemiology SAS Code for Cox models March 18 , 2014. Dr. N. Birkett, Department of Epidemiology & Community Medicine, University of Ottawa. SAS code (1). Cox models use Proc PHREG I assume that you all have at least Version 9.2 of SAS
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EPI 5344:Survival Analysis in EpidemiologySAS Code for Cox modelsMarch 18, 2014 Dr. N. Birkett, Department of Epidemiology & Community Medicine, University of Ottawa
SAS code (1) • Cox models use Proc PHREG • I assume that you all have at least Version 9.2 of SAS • Prior to this version, ‘phreg’ was more limited • An experimental version (tphreg)could be used instead. BUT, I strongly encourage you to upgrade to at least SAS 9.2
libname allison 'C:/allison_2010/data_sets'; PROC PHREG DATA=allison.recid; MODEL week*arrest(0)=fin age race wexp mar paro prio; RUN;
title 'Ties Handling: BRESLOW'; PROC PHREG DATA=allison.recid; MODEL week*arrest(0)=fin age race wexp mar paro prio / TIES=BRESLOW; RUN; title 'Ties Handling: EFRON'; PROC PHREG DATA=allison.recid; MODEL week*arrest(0)=fin age race wexp mar paro prio / TIES=EFRON; RUN; title 'Ties Handling: EXACT’; PROC PHREG DATA=allison.recid; MODEL week*arrest(0)=fin age race wexp mar paro prio / TIES=EXACT; RUN;
Breslow Efron Exact
Breslow Efron Exact
Breslow Efron & Exact
PROC PHREG DATA=allison.recid; class fin /param=ref ref=last ; MODEL week*arrest(0)=fin age race wexp mar paro prio / TIES=EFRON; RUN; PROC PHREG DATA=allison.recid; class fin /param=effect ; MODEL week*arrest(0)=fin age race wexp mar paro prio / TIES=EFRON; RUN;
An issue with ref coding (1) • By default, SAS orders the levels of a categorical variable by the ‘format’ labels if they have been assigned. • Consider:
An issue with ref coding (2) • You want to use ‘level=1’ as the reference. • This SAS code won’t do that: class x/param=ref ref=first; • Instead, the reference will be level 2. • You must use this code: class x/param=ref ref=first order=internal;
Three-level class variable • Just for test purposes, define a 3 level variable • combines race and financial aid:
PROC PHREG DATA=njb1; class racefin /param=ref ref=last ; MODEL week*arrest(0)=racefin age / TIES=EFRON; RUN; PROC PHREG DATA=njb1; class racefin /param=effect ; MODEL week*arrest(0)=racefin age / TIES=EFRON; RUN; PROC PHREG DATA=njb1; class racefin /param=orthopoly ; MODEL week*arrest(0)=racefin age / TIES=EFRON; RUN;