Instrumental variables: looking back and looking forward 

 A few months ago, I read  this review  of instrumental variables in political science by Allison Sovey and Don Green.  I enjoyed it tremendously, so I was pleased to see that it  just came out  in the  American Journal of Political Science .  The (mis)use of instruments in the political science literature has been driving me crazy, so I'm hoping that Sovey and Green's article will help raise the bar.  In some ways, the dataset they created shows that things are already getting better.  More and more articles are offering justifications for their choices of instruments and more articles are using "just-identified" models to avoid the  "embarrassment of riches"  problem that comes from using multiple instruments.  On the other hand, a plurality of articles still fail to give  any  justification for their instruments, so there is a long way to go.  Hopefully compliance with the check-list Sovey and Green provide will become the new standard in the literature. 

 But wait, there's more... 

 Sovey has  another paper  (with Peter Aronow) that may be the future of instrumental variables.  It is now well known that IV set-ups generally identify a local average treatment effect (LATE) which is rarely the quantity of interest for researchers.  Aronow and Sovey show how to recover sample average treatment effects by estimating compliance scores for each unit (even in the face of two-sided non-compliance!) and then using these weights to estimate the treatment effect if every unit in the sample had complied with their treatment.  This idea strikes me as very smart.  It also strikes me as crazy, but possibly crazy enough that it might just work.  If I ever find an instrument I actually believe for a problem I actually care about, I'll be trying this out.