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
term.
Many thanks,
David Winsemius, MD
West Hartford, CT
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