Sheps IT Lunch & Learn: Introduction to Difference-in-Differences

The Sheps Center is proud to host a Lunch & Learn series this year focused on statistical methods for analyzing data. These sessions will be facilitated by Chuck Huber from StataCorp. The workshops will be held via zoom and registration is required.

This talk will briefly introduce the concepts and jargon of difference-in-differences (DID) models and show how to fit the models using Stata’s suite of DID commands. We will demonstrate how to fit models for repeated cross-sectional data using ‘didregress’ and for panel/longitudinal data using ‘xtdidregress’. We will also fit heterogeneous DID models where the average treatment effect varies over time or cohort using ‘hdidregress’ and ‘xthdidregress’. We will discuss the model assumptions and how to check these assumptions after fitting a model. We can check the parallel-trends assumption using ‘estat trendplots’ and ‘estat ptrends’ and we can check for anticipation of treatment using ‘estat granger’. After fitting heterogeneous DID models, we will also demonstrate how to aggregate the average treatment effect among the treated (ATET) using ‘estat aggregation’ and how to visualize the trends in ATETs using ‘estat atetplot’.