I teach Econometrics at Iowa State · http://gray.clhn.org
A friend emailed me to ask about grad school; I thought I might as well share my thoughts here too. First, I should make it clear that I basically never recommend getting a PhD to anyone. Grad school pays almost nothing…
Inflamatory title! But deserved!
tl;dr: The assumptions that the authors of a recent paper on Instrumental Variables (IV) show do not hold in the general setting are not the assumptions that IV requires in the general setting.