Causal Inference, Instrumental Variables, Stats 361, Stanford, Data Science.
unconfoundedness, there are some unobserved (endogenous) relationship between Y_i and W_i. Thus, “it no longer captures a conditional expectation that can be analyzed using OLS” on page 69 (Wager, 2020). Since I could not understand this part at first, I searched about the meaning in my own way and