Fig. 5. Funnel plot of logarithm of relative risk (log RR) of postoperative nausea or vomiting or nausea alone versus precision among all studies. Data are relative risk of postoperative nausea or vomiting ( open circles ) or nausea ( closed circles ) plotted against trial precision (inverse of SD) for each trial included in the meta-analysis for postoperative nausea or vomiting 18–22,25–27,29,30,32–35,or nausea. 6,7,23,24,28,31,36 The overall SD of each trial was calculated, and the inverse was used to define the precision of the trial. A funnel plot was drawn to assess whether there was evidence of publication bias. The Egger test did not show statistical asymmetry.