YSPH Biostatistics Seminar: “Estimating the Causal Effect of Policy Interventions under Interference"

NOTE: BIS 525 students are required to attend in person. Others are invited to attend in person, but may also attend via Zoom.

SPEAKER: Nandita Mitra, PhD, Professor, Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine

TITLE: “Estimating the Causal Effect of Policy Interventions under Interference"

ABSTRACT: Public policy interventions are commonly evaluated using the difference-in-differences approach. However, this approach does not directly account for the effect of the policy ``spilling over" to neighboring regions such as nearby cities or states. For example, the implementation of an excise tax on sugar-sweetened and artificially sweetened beverages in the city of Philadelphia was shown to be associated with a substantial decrease in volume sales of taxed beverages in Philadelphia but also showed an increase in beverage volume sales in bordering counties which were not subject to the excise tax. The latter association could potentially be explained by cross-border shopping behaviors of Philadelphia city residents.

To address these important concerns, we extend difference-in-differences methods to identify the causal effects of policy interventions under various spillover conditions. We propose doubly robust estimators for the average treatment effect on the treated and on the neighboring control. The new estimators relax the standard assumptions on interference and model specification. In addition, we formally define a new causal estimator for the average treatment effect on the treated as a function of neighborhood exposure to the policy intervention. Importantly, our approach allows one to generalize the causal effect of a policy change to other target populations that may be different than the original study population. For instance, the effect of the beverage tax implemented in Philadelphia could potentially be transported to other cities with very different contextual and demographic characteristics.

YSPH values inclusion and access for all participants. If you have questions about accessibility or would like to request an accommodation, please contact Charmila Fernandes at Charmila.fernandes@yale.edu. We will try to provide accommodations requested by November 9, 2023.