[R] Contrast matrix with a continuous variable

Carlos Alvarez Roa carlosalvarezroa at hotmail.com
Sun May 22 13:31:16 CEST 2016

Hello everyone, 

I was wondering if could help me designing a
contrast matrix when you have a continuous variable (Days).  


My model looks like




The factor A hast
two levels (A1 and A2) and factor B has three levels (B1, B2, and B3). I
measured the response variable Y every two or three days over 70 days

I need to look at
only a few comparisons over the 70 days such us: 

                                   A1 and B1 vs A2 and B1,  

                                   A2 and B2 vs
A2 and B1,  

                                   A1 and B2 vs
A2 and B2

I could use the
function contrast from the package contrast to design the matrix with the three
comparisons mentioned above for specific days at a time. However, I need to run
the comparison over the 70 days not at individual time points. 


I was wondering if
you could help me designing this contrast matrix. 


Any help would be
much appreciated.

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