Jeff Wooldridge presents "Differences in Differences" to the ASA Ann Arbor Chapter 

Jeffrey Wooldridge, PhD, University Distinguished Professor of Economics at Michigan State University, has published widely in econometrics, panel data models, control function methods, and the economics of education. He has published two popular textbooks: Introductory Econometrics: A Modern Approach and Econometric Analysis of Cross Section and Panel Data.
Abstract
Dr. Wooldridge describes how the basic difference-in-differences methods are used for policy and intervention analyses, and describes recent developments that combine methods used for treatment effects estimation with regression-based methods. He also discusses issues with staggered interventions.