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Hello, I ran my simulations on the Unix verson of R1.9.1 and the Windows version of R2.0.1 on XP. I kept getting different values for the mean of the same column of the same matrix, and am perplexed. I would appreciate if anyone could help explain the difference? Here is a sample code: set.seed(7293) z1v <- rnorm(1000, mean=68, sd=13) z1v <- (z1v-mean(z1v))/sd(z1v) Using R1.9.1 on Unix,

Hello, I need to implement variable selection procedures (such as stepwise and backward selection) in Cox proportional hazards model, but can't seem to find an R or S-plus command for these procedures. I am aware that these can be done in SAS. I would appreciate help from anyone who knows how to implement these procedures in Cox models using S-plus or (preferably) R. Thanks! Regards,