Machine Learning, Causal Inference, Meta Learning, Instruments, Observational Studies.
versa. Like S- and T-learner, X-learner can use arbitrary machine learning algorithms like XGBoost as a base regressor with the lowest error in terms of SMAPE. X-learner is built on T-learner and uses each observation in the training set in an “X”-like shape, hence its name X-learner (see Künzel