Download pdf guide - VSN International

76 6 Design and sample sizeClicking OK in Figure 6.3, pops ups the menu shownin Figure 6.4, which indicates the required number ofreplicates. You can then either click Apply to enter thatnumber automatically into the design menu (Figure6.1), click Cancel to close the menu with no actions, orclick Change to return to the Replications Required menu(Figure 6.4). The result here, of 4, matches what we had Figure 6.4hoped to find (and the value that we had already enteredinto the main menu!). So we can simple click Cancel.The Replication and SEDs boxes were checked in Figure 6.3, so GenStat prints a tablegiving the power (and the standard errors of differences) for up to 20 replicates, and areport of the required replication.PowerNumber of Residual Residual s.e.d. RESPONSE t-value Powerreplicates d.f. m.s. / s.e.d.2 5 0.5000 0.7071 2.121 2.015 0.5723 10 0.5000 0.5774 2.598 1.812 0.7804 15 0.5000 0.5000 3.000 1.753 0.8885 20 0.5000 0.4472 3.354 1.725 0.9446 25 0.5000 0.4082 3.674 1.708 0.9737 30 0.5000 0.3780 3.969 1.697 0.9878 35 0.5000 0.3536 4.243 1.690 0.9949 40 0.5000 0.3333 4.500 1.684 0.99710 45 0.5000 0.3162 4.743 1.679 0.99911 50 0.5000 0.3015 4.975 1.676 0.99912 55 0.5000 0.2887 5.196 1.673 1.00013 60 0.5000 0.2774 5.408 1.671 1.00014 65 0.5000 0.2673 5.612 1.669 1.00015 70 0.5000 0.2582 5.809 1.667 1.00016 75 0.5000 0.2500 6.000 1.665 1.00017 80 0.5000 0.2425 6.185 1.664 1.00018 85 0.5000 0.2357 6.364 1.663 1.00019 90 0.5000 0.2294 6.538 1.662 1.00020 95 0.5000 0.2236 6.708 1.661 1.000ReplicationTo detect a treatment difference of 1.500, at a significance level of 0.050,with a power of 0.800, using a one-sided test, requires a replication of 4.The Replications required button is available for any design where the replication can bemodified simply by altering the levels of one of the factors (for example split-plotdesigns, split-split-plot designs, criss-cross designs and so on), but not e.g. for Latinsquares where the replication cannot be changed without changing the number of levelsof the treatment factor.