Fig. 3.
Frequency of difficult intubation over time. The x axis shows the delivery date (yr). On the y axis, the lines and band represent the predicted frequency and 95% CI, respectively, for difficult intubation over time as estimated using a logistic regression model with restricted cubic spline. The axis is on the logit scale to correspond to the logistic regression model. Scatterplot dots are shown representing observed percentages of difficult intubations for every 2-yr period.