Marino Taussig De Bodonia, Agnese <agnese.marino09 <at> imperial.ac.uk> writes:
> I am using the package "MuMI" to run all the possible combinations
> of variables in my full model, and select
> my best models. When I enter my variables in the original model I
> write them like this
> lm(y~ a +b +c +a:b)
> However, "MuMI" will also use the variable b:a, which I do not want
> in my model.
> How do I stop that from happening?
(1) I think you mean "MuMIn".
(2) Please send a reproducible example! (Hint: see the posting
guide that is referred to at the bottom of all R-help messages ...)
(3) [now proceeding to try to guess what you mean ...]
a:b and b:a have identical meanings in the R formula syntax.
I tried to do something like what I thought you might have meant
and got what seemed to be reasonable answers.