Causal Inference, Instrumental Variables, Stats 361, Stanford, Data Science.
assumption. However, since we want to express the formula without assuming unconfoundedness, {Y_i(w)}⊥W_i|X_i is not applied(given covariate X, the potential outcome Y_i is not independent of whether i-th sample is actually treated or not), and so E[ε_i|W_i]≠0. In other words, when not assuming