sorry, repeated for clarifcation:
> test<-coxph(Surv(cull,status) ~ YoB,na.action=na.omit,SDF2)
> test
Call:
coxph(formula = Surv(cull, status) ~ YoB, data = SDF2, na.action = na.omit)
coef exp(coef) se(coef) z p
YoB1 3.263 26.136 24.427 0.1336 0.89
YoB2 1.004 2.729 8.149 0.1232 0.90
YoB3 0.227 1.255 4.080 0.0556 0.96
YoB4 0.136 1.146 2.452 0.0556 0.96
YoB5 -0.772 0.462 3.989 -0.1935 0.85
YoB6 0.188 1.207 1.279 0.1471 0.88
YoB7 0.204 1.226 0.959 0.2127 0.83
YoB8 0.340 1.405 0.745 0.4568 0.65
Likelihood ratio test=18 on 8 df, p=0.0208 n=122 (1 observations deleted due
to missing values)
YoB : "1991", "1992", "1993", "1994", "1995", "1996", "1997", "1998", "1999"
------------------------------------------------------------------
original question:
> so is Splus comparing each year to 1991 (so YoB1 is 1992), or to 1999 (so
> YoB1 is 1991), or just to each previous year in the list (so YoB1 is 1992,
> and is compared to 1991, with YoB2 being compared to YoB1 anad so on)?
Reply from Prof. Frank E Harrell Jr
Please read the posting guide; show your code. It would also be good to
use intuitive category names.
You might look at the Design library which has a wrapper function for
coxph called cph. The output makes the coding apparent. cph uses the
first level as the reference cell. For many things you don't need to
know that (e.g., contrast, summary, plot, nomogram, latex functions in
Design).
--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
Thanks
Natalie
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