Alejandra Solis Herrera wrote:
Hi,
I'm trying to fit a binary logistic regression model, and would like to
consider certain characteristics B and C only for people with variable A=1 and
not for those with variable A=0, so I'm trying to do the following:
model<- lrm(formula= y ~ A: (B+C) + D + E +...)
I've had no problem with adding interaction terms using " * ", but every time I try to
use " : ", as in my example, I get an error message like:
The Design package doesn't support that. It uses the (highly
recommended) hierarchy principle so it assumes you will use * for
interactions.
Frank
Error in if (!length(fname) || !any(fname == zname)) { :
Missing value where TRUE/FALSE needed
I would really appreciate any advice on how to solve this, I don't know what in
the notation should be different for different operators.
Thanks in advance, kind regards,
Alejandra Solís
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