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Details of the FACTEX Procedure 
See FACTEX15 in the SAS/QC Sample Library 
In an unreplicated blocked design, the interaction effect that is confounded with the block effect cannot be estimated. You can replicate the experiment so that a different interaction effect is confounded in each replicate. This enables you to obtain information about an interaction effect from the replicate(s) in which it is not confounded.
For example, consider a 2^{3} design with factors A, B, and C arranged in two blocks. Suppose you decide to run four replicates of the design. By constructing the design sequentially, you can choose the effects to be estimated in each replicate depending on the interaction confounded with the block effect in the other replicates.
In the first replicate, you specify only that the main effects are to be estimable. The following statements generate an eightrun twolevel design arranged in two blocks:
proc factex; factors a b c; blocks nblocks=2; model est=(a b c); examine confounding aliasing; output out=rep1 blockname=block nvals=(1 2); run;
The alias structure and the confounding scheme are listed in Output 15.12.1. The highest order interaction A*B*C is confounded with the block effect. The design, with recoded block levels, is saved in a dataset named REP1.
Output 15.12.1: Confounding Rule and Alias Structure for Replicate 1

model est=(a b c a*b*c); output out=rep2 blockname=block nvals=(3 4); run;
The alias structure and the confounding scheme for the second replicate are listed in Output 15.12.2. The interaction A*B*C is free of any aliases, but now the twofactor interaction B*C is confounded with the block effect.
Output 15.12.2: Confounding Rule and Alias Structure for Replicate 2

model est=(a b c a*b*c b*c); output out=rep3 blockname=block nvals=(5 6); run;
The alias structure and confounding rules are shown in Output 15.12.3. The interaction B*C is free of aliases, but the interaction A*C is confounded with the block effect.
Output 15.12.3: Confounding Rule and Alias Structure for Replicate 3

model est=(a b c a*b*c b*c a*c); output out=rep4 blockname=block nvals=(7 8); run;
The alias structure and confounding rules are displayed in Output 15.12.4.
Output 15.12.4: Confounding Rule and Alias Structure for Replicate 4

data combine; set rep1 rep2 rep3 rep4; run; proc print data=combine; run;
The final design is saved in the data set COMBINE. A listing of this data set is shown in Output 15.12.5.
Output 15.12.5: Combined Design
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