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Details of the FACTEX Procedure |
See FACTEX12 in the SAS/QC Sample Library |
You can replicate a design to obtain an independent estimate of experimental error or to estimate effects more precisely. There are two ways you can replicate a design using the FACTEX procedure: you can replicate the entire design with the DESIGNREP= option, or you can replicate each point in the design with the POINTREP= option. The following example illustrates the difference.
A process engineer is conducting an experiment to study the shrinkage of an injection-molded plastic component. The engineer chooses to determine the effect of the following four factors, each at two levels: holding pressure (PRESSURE), molding temperature (TEMP), cooling time (TIME), and injection velocity (VELOCITY).
The design used is a half-fraction of a 24 factorial design, denoted as 24-1IV. The following statements construct the design:
proc factex; factors pressure temp time velocity; size fraction=2; model res=max; output out=savunrep; run; proc print data=savunrep; run;
The design, saved in the data set SAVUNREP, is shown in Output 15.6.1.
Output 15.6.1: Unreplicated Design
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proc factex; factors pressure temp time velocity; size fraction=2; model res=max; output out=savedrep designrep=3; run; proc print data=savedrep; run;
The design, saved in the data set SAVEDREP, is displayed in Output 15.6.2.
Output 15.6.2: Design ReplicationNow, instead of replicating the entire design, suppose the engineer decides to replicate each run in the design three times. The following statements construct a 24-1IV design in 24 runs with point replication:
proc factex; factors pressure temp time velocity; size fraction=2; model res=max; output out=saveprep pointrep=3; run; proc print data=saveprep; run;
The design, saved in the data set SAVEPREP, is displayed in Output 15.6.3. The first design point is replicated three times (observations 1 -3), the second design point is replicated three times (observations 4 -6), and so on.
Output 15.6.3: Point Replication
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