Dr. Guido Cataife presented this poster that discusses using the less stringent generalized difference-in differences model (GDD) for policy evaluations in situations where a difference-in-differences (DD) model might be used.
Cataife, G., Hesgrove, B. & Varghese, R. (2018, June). Generalization of the Difference-in-Differences Model for Applied Research. Poster presentation at the AcademyHealth Annual Research Meeting (ARM), Seattle, WA.
Difference-in-differences (DD) models are a very popular method for policy evaluation. However, the identifying assumption (parallel trends assumption) is rarely satisfied. In this poster, we discuss the properties of the generalized DD model (GDD), which adds linear time trends and relaxes the stringent parallel trends assumption, and provide insights relevant for the applied researcher.