Estimation method of principal quantile treatment effect using principal scores and its application.

Music City Center 

Several attempts have been made to estimate causal effect on principal stratum. These methods deal with causal inference on principal stratum in terms of the population means of potential outcomes. However, sometimes the median or other quantiles of outcomes in a principal stratum according to potential occurrence of intercurrent events are of interest in randomized clinical trials. Regarding the estimation of quantile treatment effects on principal stratum, some authors proposed an estimator under the assumption of "exclusion restriction" (ER). However, Ding and Lu (2017) argued that the ER assumption seems unfeasible in some applications. Therefore, we propose principal quantile treatment effect estimators that can nonparametrically estimate the distribution of potential outcomes by principal score weighting without relying on the ER assumption. Our simulation studies show that the proposed method works in situations where the median or quantiles may be regarded as the preferred population-level summary over the mean. We illustrate our proposed method by using simulated data based on a randomized controlled trial conducted on patients with nonerosive reflux disease.

estimand

principal stratum

principal stratification

monotonicity

principal ignorability

non-normal 

Biopharmaceutical Section