[R] Baseline terms for lrm
dwinsemius at comcast.net
Tue Jan 18 21:25:02 CET 2011
On Jan 18, 2011, at 2:51 PM, Rob James wrote:
> Dear R-help and Prof. Harrell:
> My question concerns the baseline state for continuous variable in
> lrm() within the RMS package.
> I have a model which can be reduced to:
> lrm(FT ~ rcs(V1, c(0, 1,5))
> The model makes perfect sense if the baseline state is where V1>=5
> but the model makes no sense if the baseline category is 0 (which I
> had expected).
You are using terminology that suggests you ar working with a
categorical variable but asking a question about a function that only
makes sense when applied to contiguous variables. I think you need to
provide results from str and describe() on V1.
> Can someone point me to a reference, or suggest a command/test, to
> get the model to fess up to the baseline state. The variable V1 and
> V1' are shown in the model output, but there is no clear association
> between these pseudo-variables and the ranges specified in the cut.
Further suggestive evidence that you are working with categorical data
if there was construction of the variable with cut() function.
> Thus, it is seems possible to misidentify the baseline value for the
> Many thanks,
David Winsemius, MD
West Hartford, CT
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