Fig. 2.

To assess the improvement in covariate balance owing to propensity score matching, the standardized mean difference between cohorts across covariates was calculated before and after matching. Cohorts were considered balanced with respect to a given covariate if the standardized mean difference was less than 0.1 (demarcated in the image with a vertical line), a common benchmark in propensity score matching studies. SSI = surgical site infection.