Confounding is a major concern in nonexperimental studies of
endoscopic interventions and can lead to biased estimates of the effects of
treatment. Propensity score methods, which are commonly used in the
pharmacoepidemiology literature, can effectively control for baseline
confounding by balancing measured baseline confounders and risk factors and
creating comparable populations of treated and untreated patients. We propose the
following 5-step checklist to guide the use and
evaluation of propensity score methods: (1) select covariates; (2) assess
covariate balance in risk factors before
propensity score implementation; (3) estimate and implement the propensity
score in the study cohort; (4) re-assess covariate balance
in risk factors after propensity score implementation; and
(5) critically evaluate differences between matched and unmatched patients
after propensity score implementation. We then apply this checklist to an
endoscopy example using a study cohort of 411 adults with newly diagnosed
eosinophilic esophagitis (EoE), some of whom were treated with esophageal
dilation. We identified 156 patients, aged 18 and older, who were treated with
esophageal dilation, and 255 patients who were nondilated. We successfully
matched 148 (95%) dilated patients to nondilated patients who had a
propensity score within 0.1, based on patient age, sex, race, self-reported
food allergy, and presence of narrowing at baseline endoscopy. Crude
imbalances were observed before propensity score matching in several
baseline covariates, including age, sex, and narrowing; however, propensity
score matching was successful in achieving balance across all measured
covariates. We provide an introduction to propensity score methods, including a
straightforward checklist for implementing propensity score methods in
nonexperimental studies of treatment effectiveness. Moreover, we demonstrate
the advantage of using the typical patient characteristics
table as a simple but effective diagnostic tool for evaluating the
success of propensity score methods in an applied example of esophageal
dilation in EoE.