But we need to allow for individual variations, so we extend this function to read S = fS(EX, ED, US), where US stands for “unobserved variables that affect salary.”
uhh. so we just alter the causal graph... adding noise to replace hidden variables makes all sorts of assumptions!?!
- those variables have "little effect" on EX, ED and S.
- they are not biased in any way
- ?
