
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":

(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 

This happens with all my data frames, there is always a problem with the first pair of variables. Does anyone have an idea why R does not compute the coefficients of "variable.A : variable.a"?
Thanks in advance!

Best regards,
Jennifer
 		 	   		  
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