[R] regression analysis with interactions

[Erik Iverson]

Jennifer Hou wrote:
> Hello,
> 
> I have got a linear model that looks like this:
> lm(criterion ~ variable.A*variable.a + variable.B*variable.b + variable.C *variable.c)
> 
> The output computed with stdCoeff() seems to be all right, but it does not show the coefficients of the interaction of the first pair of variables. Instead, it shows "NA":
> 

And what package is the `stdCoeff` function in? If we don't have a 
reproducible example, it's very hard to help.

What does calling the summary function on your lm object give you?


> (Intercept) 
> NA 
>                                                       
> variable.A
>  0.0925094150 
> variable.a
> 0.1517246479 
> variable.B
> -0.0023847092 
> variable.b
> 0.0256653197 
> variable.C
> 0.0194313471 
> variable.c
> 0.0192897539 
> 
> variable.A : variable.a
> NA 
> variable.B : variable.b
> 0.0471111439 
> variable.C : variable.c
> 0.0696702457 
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