The German practice of compelling weak students to repeat a class has come under heavy criticism recently. Many observers fear that this practice is, at best, useless or even counterproductive. However, little is known so far on the consequences of having to repeat a class, as compared to be...

This note provides a simple exposition of what IV can and cannot estimate in a model with binary treatment variable and heterogenous treatment effects. It shows how linear IV is essentially a misspecification of functional form and the reason why linear IV estimates will generally depend on the...

This paper analyzes conditions under which various k-class estimators are asymptotically normal in a simultaneous equations framework with many weak instruments. In particular, our paper extends the many instruments asymptotic normality results obtained by Morimune (1983), Bekker (1994), Angrist...