natalie nicholls (IAH-C) wrote:
Dear users,
In coxph - what does S use as the reference level in its output:
For example:
coef exp(coef) se(coef) z p
V151 3.263 26.136 24.427 0.1336 0.89
V152 1.004 2.729 8.149 0.1232 0.90
V153 0.227 1.255 4.080 0.0556 0.96
V154 0.136 1.146 2.452 0.0556 0.96
V155 -0.772 0.462 3.989 -0.1935 0.85
V156 0.188 1.207 1.279 0.1471 0.88
V157 0.204 1.226 0.959 0.2127 0.83
V158 0.340 1.405 0.745 0.4568 0.65
where V151 etc, are different levels of a factor. I am looking at the effects
of Year of Birth, the levels are:
"1991", "1992", "1993", "1994", "1995", "1996", "1997", "1998", "1999"
so is Splus comparing each year to 1991 (so V151 is 1992), or to 1999 (so V151
is 1991), or just to each previous year in the list (so V151 is 1992, and is
compared to 1991, with V152 being compared to V151 anad so on)?
Natalie
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
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