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: 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 SolĂs [[alternative HTML version deleted]]
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