internal validity

Revise and Resubmit: Journal of Econometrics.
Attrition is an important threat to internal validity in treatment effect studies. We extend the changes-in-changes approach to identify the treatment effect in the presence of attrition. Our method can be applied in randomized experiments as well as difference-in-difference designs.

Revise and Resubmit: Journal of Human Resources.
A systematic review of the field experiment literature indicates that there is no consensus on how to test for attrition bias. We establish identifying assumptions for treatment effects and propose procedures to tests their sharp implications. Several applications support the empirical relevance of our analysis.