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74 6 Design and sample size6.1 Designing an experimentThe Generate a Standard Designmenu enables you to generate manystandard experimental designs. It isobtained by clicking Stats on themenu bar and selecting Design,followed by Standard Design. Thetype of design is selected using theDesign list box. The categoriesparallel those in the Analysis ofVariance menu again each with itsappropriate boxes and buttons.The menu in Figure 6.1 generatesa randomized-block design withfour blocks (corresponding to fourdifferent laboratories) to study twotreatment factors: Drug with threelevels, and Dose with two levels.Checking the Randomize Design box Figure 6.1asks GenStat to randomize thedesign. GenStat automatically determines the appropriate type of randomization from theinter-relationships of the blocking factors of the design. For a randomized-block design,this amounts to randomizing the allocation of the treatments independently within eachblock; see Section 6.3. (However, if you want to do your own randomization, you canuse the Randomize menu, obtained by clicking Stats on the menu bar and selecting Design,followed by Randomize.) The Randomization Seed box supplies a seed used to generate therandom numbers for the randomization. GenStat suggests a seed automatically (atrandom), in the same way that it suggests defaults for the other fields in the menu.However, you can supply your own seed if you prefer, and keeping the same seed willgenerate the same randomization if you want to reproduce the exact design in future. Themenu prints the design and, because the Dummy ANOVA table box is checked, it will alsogenerates a skeleton analysis-of-variance.