Fig. 3. Epidural use and age interaction (age categories). Kaplan-Meier time-to-recurrence plots with 95% equal-precision confidence bands comparing epidural versus nonepidural use by age categories (A : younger age group: age up to 64 yr; B : older age group: age older than 64 yr). The reversing of the relationship of interest for the two age groups suggests an interaction between epidural use and age.