Distribution of total sample size required when using pilot sample derived SD p estimated with and without inflation. (a) Effect size = 0.2. (b) Effect size = 0.35. (c) Effect size = 0.5. This figure is similar to Figure 4; however, now the total sample size includes the pilot study size. The dashed and dotted vertical lines represent the sample size required for 90% and 80% power, respectively, if the true SD were known and the pilot study were not necessary.