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78 6 Design and sample sizeFigure 6.7Figure 6.6The Generate a Standard Design menu has a Check Power button, which you can press onceyou have generated the design. This pops up the Power for Design menu, which allows youto calculate the power, or probability with which various sizes of treatment responses willbe detected. In Figure 6.6 we have set the treatment term to be Drug.Dose, and the sizeof difference to be 1.75. When we click OK GenStat pops up the menu shown in Figure6.7, telling us that the power would be 0.95.6.2 PracticalConstruct a randomized block design for three factors Additive, Timing and Amountwith three, two and two levels, respectively. (Hint: select the design setting GeneralTreatment Structure (in Randomized Blocks) in the Generate a Standard Design menu. Set thenumber of replicates so that the design has a 90% chance (or power) to detect a differenceof 1.5 in the effects of the 3-way interaction, assuming a variance within blocks (residualmean square) of 0.5 and using the F ratio with a significance level of 5%.Your client now tells you that he cannot manage more than five replicates. What willthe power now be for the detection of the interaction?6.3 Control treatmentsWe now look at some of the otherpossibilities in the Standard DesignOptions menu. The Extra check boxenables you to add extra replicatesto the first level of any of thetreatment factors. This could beuseful if the first level is a controltreatment against which the otherlevels are to be compared. Whenyou check Extra box, the two otherboxes in the top line of the menubecome accessible, for you to selectthe factor of interest (in the righthandbox), and specify the numberof extra replications. In Figure 6.8Figure 6.8