Fig. 1. The probability of no patient movement in response to skin incision is plotted against the concentration of xenon. The continuous and broken curves represent the logistic regression curves for men and women, respectively. By definition, the concentration associated with a 50% probability of no movement (the intersection between the horizontal bar and the regression curve) is the minimum alveolar concentration (MAC) of xenon for each sex. The horizontal bars represent the 95% confidence intervals of the MACs.