2.5. Sample Size Calculation
SD
In an interim analysis of 26 patients (unpublished data), the mean and standard deviation (SD) values of the primary outcome were −11.7 (SD, 14.2) and 1.7 (SD, 10.6) in the bilateral and unilateral groups, respectively. Based on these data and by assuming a population SD of 10, statistical power of 0.8, and significance level of 0.05, a sample size of 32 patients (both groups combined) was required. To account for possible attrition, we set the target overall caseload at 40 cases (20 in each group). Block randomization and sample size calculations were performed under the direction of a statistician who was not involved in the trial.