Difference in differences methods have become very popular in applied work. This paper provides a new method for inference in these models when there are a small number of policy changes. This situation occurs in many implementations of these estimators. Identification of the key parameter...

Difference in differences methods have become very popular in applied work. This paper provides a new method for inference in these models when there are a small number of policy changes. This situation occurs in many implementations of these estimators. Identification of the key parameter...

With only a small number of their students coming from families with the lowest incomes (10% from the bottom two family income quintiles), the nation's most selective private colleges and universities need to know why. Two ready ideological answers are (1) that low-income high-ability students...