Fig. 1

Propensity score matching. (A) Q‒Q plot comparing the probability distributions of the two surgical groups with regard to covariates. The results show that although the matched point is not precisely on the y = x-line, it significantly improves compared to that before matching. (B) Histogram showing the distribution density of the propensity scores before and after matching the two surgical groups. The propensity scores of the prematch treatment group were significantly greater than those of the control group. After matching, the density distributions of the two groups became similar. (C) Jittered plot showing the matched and nonmatched observations. The distribution of the propensity scores was similar between the matched groups.