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Details of the FACTEX Procedure 
See FACTEX10 in the SAS/QC Sample Library 
Folding over a fractional factorial design is a method for breaking the links between aliased effects in a design. Folding over a design means adding a new fraction identical to the original fraction except that the signs of all the factors are reversed. The new fraction is called a foldover design. Combining a foldover design with the original fraction converts a design of odd resolution r into a design of resolution r+1.^{*} For example, folding over a resolution 3 design yields a resolution 4 design. You can use the FACTEX procedure to construct the original design fraction and a DATA step to generate the foldover design.
Consider a 1/8 fraction of a 2^{6} factorial design with factors A, B, C, D, E, and F. The following statements construct a 2^{63}_{III} design:
proc factex; factors a b c d e f; size fraction=8; /* Specify 1/8 fraction design */ model resolution=3; /* of resolution 3 */ examine aliasing; output out=original; run; title 'Original Design'; proc print data=original; run;
The design, which is saved in the data set ORIGINAL, is displayed in Output 15.4.1.
Output 15.4.1: A 2^{63}_{III} Design


data foldover; /* Create the foldover design with */ set original; /* the factor signs reversed */ a=a; b=b; c=c; d=d; e=e; f=f; run; title 'FoldOver Design'; proc print data=foldover; run;
The foldover design is displayed in Output 15.4.3.
Output 15.4.3: A 2^{63}_{III} Design with Signs Reversed

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