Dear all,
this might be not only an R-question but also a statistical.
When I do a logistic regression analysis (species distribution modeling)
with function lrm (Design package) I get the follwoing error message:
> tadl1<-lrm(triad~fd+dista+fd2+dista2+fd:dista+dista:geo2, x=T, y=T)
Error in if (!length(fname) || !any(fname == zname)) { :
missing value where TRUE/FALSE needed
The problem seems to be that geo2 (factor variable with 3 levels) is not
included as main effect. But when I run the same model with glm it is
working properly.
However, from an ecological point of view, inclusion of only the
interaction term makes sense. When running the model with inclusion of
both main effect and interaction, main effect has no significant
influence and the interaction only marginaly. And LR-Test underlines
model simplification.
Does anyone know how to solve the problem? I need the lrm function since
I have to validate my models via bootstrapping (validate.lrm).
Many thanks!
Eva
--
Eva Mosner
Lilienstraße 9
35043 Marburg
06421-8400886
0151-17867488
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