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Interactions in factorial design

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Interactions in factorial design

Hi - I can specify a full factorial model with factors A, B, C and D in PROC GLM, PROC GLMSELECT etc using notation like this: A | B | C | D.  But can I tell the procedure that I only want to include interactions of A, B, C and D upto and including the second order?  Obviously I could write them all out in full (A*B  A*C A*D B*C etc), but I'm guessing there's probably an easier way.  Is there?

Many thanks.


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‎08-31-2012 08:00 AM
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Posts: 2,655

Re: Interactions in factorial design

There sure is.  For your situation, use A|B|C|D@2.  This will give a model with main effects and all two way interactions.  In the documenation for GLM, look at Example 42.11 Analysis of a Screening Design, where they present a four factor model, and fit main effects and the two way interactions.

Steve Denham

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Solution
‎08-31-2012 08:00 AM
Respected Advisor
Posts: 2,655

Re: Interactions in factorial design

There sure is.  For your situation, use A|B|C|D@2.  This will give a model with main effects and all two way interactions.  In the documenation for GLM, look at Example 42.11 Analysis of a Screening Design, where they present a four factor model, and fit main effects and the two way interactions.

Steve Denham

SAS Employee
Posts: 268

Re: Interactions in factorial design

Perfect - just what I needed.

Many thanks!

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