Learning the Effect of Persuasion via Difference-In-Differences

Abstract

We develop a difference-in-differences framework to measure the persuasive impact of informational treatments on behavior in staggered treatment settings. We introduce two causal parameters, the forward and backward average persuasion rates on the treated, which refine the average treatment effect on the treated. The forward rate excludes cases of "preaching to the converted," while the backward rate omits "talking to a brick wall" cases. The backward rate coincides with the probability of necessity from the literature on probabilities of causation. We identify both persuasion rates under a no-backlash condition and a parallel-trends assumption imposed on a known transformation of response probabilities, taking the identity link as the baseline and nonlinear links as sensitivity checks. We develop estimation and inference using GMM and a limited-information method. We demonstrate the usefulness of our framework with an application to a Chinese curriculum reform introduced across provinces at different times.