Fig. 4.  Cumulative probability curves, genetically and ethnicity optimized models. The cumulative probability of a given value for each variable is plotted on the y-axis (solid black line ). Active and latent labor rates constant in nominal subjects (A,  black line ; B , red line ); latent labor rate constant in nominal black subjects (green line ). Black women have a very slow rate of latent labor 0.01 h⁻¹(−0.130 to 0.070) compared with non-black women who have a latent labor rate constant of 0.08 h⁻¹(0.02–0.16). (C ) The cervical dilation at which the patient transitions between latent and active labor in nominal (black line ) and nominal Asian subjects (blue line ). Asian patients transition to active labor at 5.2 (3.7–7.0) cm, whereas nominal non-Asian patients transition to active labor earlier, at 3.3 (2.52–4.20) cm. (D ) Epidural time factor. Neuraxial analgesia is associated with slower labor progress by a factor of 0.32.