Is there a difference between I(x*y) and I(y*x) ? I have a call to lmer that results in this complaint: Error in is.alpha2.subordinate * ~z.min.co.res : non-numeric argument to binary operator when I change this line: I(is.alpha2.subordinate*z.min.co.res)+ to this: I(z.min.co.res*is.alpha2.subordinate)+ the complaint goes away. I'd like to understand why.
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