SAMPLE SIZE Postoperative nausea and vomiting incidence from day case laparoscopic gynaecologic procedures (primary outcome) both with and without single agent antiemetic prophylaxis varies from 40 -90%.2,3,7 To detect a clinically significant difference of 25% reduction in mean nausea scores based on a PONV incidence of 40% without antiemetic prophylaxis, we calculate a sample size of 60 patients per group (a = 0.05, β = 0.2).