Re: [R] Survival dummy variables and some questions

From: Frank E Harrell Jr <f.harrell_at_vanderbilt.edu>
Date: Mon 18 Jul 2005 - 22:46:13 EST

Stephen wrote:
> Hi All,
>
>
>
> I am currently conducting some survival analyses. I would like to
> extract coefficients at each level of the IVs.
>
> I read on a previous posting that dummy regression using coxph was not
> possible.

I'm not sure what that means.

>
> Therefore I though, hey why not categorize the variables
>
> (I realize some folks object to categorization but the paper I am
> replicating appears to have done so ...)

The fact that some people murder doesn't mean we should copy them. And murdering data, though not as serious, should also be avoided.

Make sure that eventbefore is a "pre time zero" measurement.

Frank

>
> and turn the variables into factors and then try the analysis.
>
>
>
> E.g.,
>
> Dataset <- read.table("categ.dat", header=TRUE)
>
> Dataset$eventbefore2c <- factor(Dataset$eventbefore)
>
> .. other IVs here
>
> ...
>
> surv.mod1 <- coxph(Surv(start, stop, event) ~ sex2 + ageonset2c +
> eventbefore2c + daysbefore2c, data=Dataset)
>
>
>
> Strangely enough, I receive a warning message when the variables are
> treated in this way: X matrix deemed to be singular; variable 11 in:
> coxph(Surv(start, stop, event) ~ sex2 + ageonset2c + eventbefore2c +
>
>
>
> I donít receive any warnings just treating the variables in their
> initial continuous format.
>
> I am currently using version
>
> platform i386-pc-mingw32
>
> arch i386
>
> os mingw32
>
> system i386, mingw32
>
> status
>
> major 2
>
> minor 1.1
>
> year 2005
>
> month 06
>
> day 20
>
> language R
>
>
>
>
>
> Is this approach to dummy variable using coxph erroneous?
>
>
>
> Is there another way to conduct dummy variable regression with coxph?
>
>
>
> Also, if I include frailty (id) does anyone know of a useful way to
> investigate frailty?
>
>
>
> If one were to plot recurrent events does anyone know of a way of
> interpreting them?
>
>
>
> References & code appreciated.
>
>
>
> BTW. not too familiar with R, less so with survival analysis .... but
> well worth the effort.
>
>
>
> Many thanks in advance...
>
>
>
> Regards
>
>
>
> Stephen
>
>
> ???? ?"? ???? ????
> http://mail.nana.co.il
>
> [[alternative HTML version deleted]]
>
>
>
> ------------------------------------------------------------------------
>
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-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University

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Received on Mon Jul 18 22:49:14 2005

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