Programming the statistical procedures from SAS

Contrast statement

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Regular Contributor
Posts: 204

Contrast statement

Hi there.

 

Can someone please explain to me about the contrast statement? 

For example, to test the linear/quadratic/cubic trend of a 4-level variable, the contrast statements will be

Linear -3 -1 1 3 
Quad 1 -1 -1 1 
Cubic -1 3 -3 1.

 

I just can't get my head around how it is -3 -1 1 3 for linear, 1 -1 -1 1 for quadratic and -1 3 -3 1 for cubic. I only understand they need to sum up to zero.

 

Thank you heaps.

Respected Advisor
Posts: 3,773

Re: Contrast statement

[ Edited ]

Run this program.

 

data op;
   input linear quadratic cubic;
   x + 1;
   cards ;
-3  1 -1
-1 -1  3
 1 -1 -3
 3  1  1
;;;;
   run;
proc print;
   run;
proc sgplot;
   pbspline x=x y=linear;
   pbspline x=x y=quadratic;
   pbspline x=x y=cubic;
   run;

Capture.PNG 

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