Preference score distribution. The preference score is a transformation of the propensity score
that adjusts for differences in the sizes of the two treatment groups. A higher overlap indicates subjects in the
two groups were more similar in terms of their predicted probability of receiving one treatment over the other.
Systematic error. Effect size estimates for the negative controls (true hazard ratio = 1)
and positive controls (true hazard ratio > 1), before and after calibration. Estimates below the diagonal dashed
lines are statistically significant (alpha = 0.05) different from the true effect size. A well-calibrated
estimator should have the true effect size within the 95 percent confidence interval 95 percent of times.