Finally, I found the answer from here... http://www.childrensmercy.org/stats/weblog2005/StratifiedCoxRegression.asp http://www.childrensmercy.org/stats/weblog2005/StratifiedCoxRegression.asp
Thernau and Grambsch describe it well in their book on survival analysis. /Analysis of multicenter clinical trials frequently uses stratification. Because of varying patient populations and referral patterns, the different clinical centers in the trial are likely to have difference baseline survival curves, ones that do not have simple parallel relationships. Strata play a role similar to blocks in randomized block designs analyzed by two-factor analysis of variance. (page 44)./ -- View this message in context: http://r.789695.n4.nabble.com/Package-survival-Difference-of-coxph-strata-with-subset-tp3657397p3658798.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
