Figure 1:

The difference-in-differences method. This method compares the difference in the mean labor neuraxial analgesia utilization rate in women aged 21 to 25 years (red circles) before and after the implementation of the Dependent Coverage Provision (difference 1) to the difference in the mean labor neuraxial analgesia utilization rate in women aged 27 to 31 years (blue squares) before and after the implementation of the Provision (difference 2). The difference between difference 1 and difference 2 (i.e., difference-in-differences) is estimated using the regression coefficient of a two-way interaction term between the age group (indicator of the 21 to 25 years old group) and the period (indicator of the post intervention period) in a linear regression model. For example, a regression coefficient of 0.015 indicates that the Dependent Coverage Provision is associated with a 1.5% (absolute) increase in the probability of labor neuraxial analgesia in women aged 21 to 25 years compared to women aged 27 to 31 years.