Prevention of further postoperative nausea and vomiting with 5-HT3 receptor antagonists. Symbols are absolute risk reductions (ARR) or numbers-needed-to-treat (NNT), respectively, with 95% confidence intervals. Symbol sizes are proportional to the number of analysed patients. White circles: vomiting; grey squares: nausea. ∞ = infinity (ARR = 0). All data are from adults.