Sample size and statistical analyses
PONV, SD
Because the incidence of PONV in low-risk patients has not been reported previously, we conducted the preliminary study. In a preliminary study, 20 patients (with the same inclusion and exclusion criteria) were administered intravenous saline (2 mL) at the end of the surgery, and the incidence of PONV was 35%. The data from the preliminary study were not included in the present study. A sample size calculation was performed using a power analysis (α = 0.05, 1-β = 0.9). A 25% difference in the incidence of PONV for the saline group versus the dexamethasone-ramosetron group indicated that 54 patients per group were required. Assuming a potential dropout rate of 10%, the final sample size was set at 177 patients. The data are expressed as the mean ± standard deviation (SD) or number (%) of patients.For intergroup comparisons, the normality of the distribution of continuous variables was assessed using the Levene test. Normally distributed data are presented as the mean ± SD and analyzed using one-way analysis of variance. Categorical variables were analyzed using the chi-squared test or Fisher’s exact test, as appropriate. All significant results were further analyzed using Scheffe’s post-hoc test to detect intergroup differences. The 