Fig. 1. Receiver operating curve (ROC) showing the relationship between sensitivity (true positive) and 1-specificity (true negative) in determining the predictive value of the number of criteria (1 to 5) for difficult mask ventilation. The area under the curve was 0.76 ± 0.11 (P < 0.05). The chosen threshold was n = 2 criteria, which provided a sensitivity of 0.72 and a specificity of 0.73.