topic Why my contrast statement gave me only one p-value? in Statistical Procedures

Why my contrast statement gave me only one p-value?

twotwotwo — Tue, 28 Feb 2012 17:54:32 GMT

Hi,

I performed a mixed model procedure and in this procedure, I used group as the fixed effect. The group is a categorical variable and has 4 level. And I want to compare the difference between each group with the contrast statement. Here is my code:

proc mixed data=test;

by brand;

class name;

model price=group;

contrast 'group1 vs2' group 1 -1 0 0;

contrast 'group1 vs3' group 1 0 -1 0;

contrast 'group1 vs4' group 1 0 0 -1;

run;

However, I got 3 SAME contrast p-value. But those 4 groups are different from each other. Why I got the same p-value for those 3 comparisons? Thanks!

Why my contrast statement gave me only one p-value?

art297 — Tue, 28 Feb 2012 18:05:45 GMT

Seeing the data might help someone trying to answer your question.

Why my contrast statement gave me only one p-value?

Doc_Duke — Tue, 28 Feb 2012 18:59:02 GMT

I think that the problem is in your CLASS statement. I think that it should read

CLASS group;

Doc Muhlbaier

Duke

Re: Why my contrast statement gave me only one p-value?

twotwotwo — Tue, 28 Feb 2012 18:59:25 GMT

Thanks for your response. Please see the attached. I only put part of my data. Thanks.

Why my contrast statement gave me only one p-value?

twotwotwo — Tue, 28 Feb 2012 19:23:31 GMT

Please see my attachment for the data. Thanks!

Why my contrast statement gave me only one p-value?

twotwotwo — Tue, 28 Feb 2012 19:26:42 GMT

Thanks for your reply. I really want CLASS name; How can I correct them? thanks!

Why my contrast statement gave me only one p-value?

Reeza — Tue, 28 Feb 2012 19:45:34 GMT

SAS isn't considering GROUP a categorical variable if its not in the class statement.

You might want to include in your BY statement perhaps, ie a separate model for each value of name? or you can have both in the class statement.

CLASS group name;

Not sure, depends on what you're trying to do.

Why my contrast statement gave me only one p-value?

twotwotwo — Tue, 28 Feb 2012 20:14:54 GMT

Thanks! It then gave me three different p-value.