Primary Submission Category: Difference in Differences
Robust Transportation of Public Policy Effects to New Contexts
Authors: Gary Hettinger, Youjin Lee, Nandita Mitra,
Presenting Author: Gary Hettinger*
Public policies are crucial tools for numerous societal goals like improving health and economic outcomes. As a result, there have been substantial recent methodological developments for evaluating policy effects in regions where such policies are implemented. However, policies often have largely different consequences when implemented in new regions that may differ in their demographic and geographic characteristics as well as their implementation strategy. These differences limit the use of traditional methods and analyses for future decision-making.
To improve upon these limitations, we develop methodology to transport policy effects from an implementing region to a new region that may be considering a similar policy. Our methods build upon classical difference-in-differences approaches and semiparametric theory to first flexibly estimate effect heterogeneity and then adapt these findings to the nuances of a new region. In addition to semiparametric estimators, we also present a new set of identification assumptions necessary for valid transportation and tools for assessing the validity of potential projections. We apply our methods to study effects of excise tax policies in the US.