Which one are the compliers?

Short riff on the LATE

Guido Imbens and Josh Angrist won the Nobel Prize in economics for two papers: their 1994 Econometrica presenting the LATE theorem, and their 1996 JASA with Don Rubin which fleshed out some of these subpopulations a bit more. And it is now well known that instrumental variables when cast in potential outcomes and allowing for heterogenous treatment ef…