Modeling event studies with heterogeneous treatment effects

This paper develops a simple approach to overcome the shortcomings of using a standard, single treatment-effect event study to assess the ability of an empirical model to measure heterogeneous treatment effects. Equally as important, we discuss how the standard errors reported in a typical event-study analysis for the posttreatment event-time effects are, without additional information, of limited use for assessing posttreatment variations in the treatment effects. The simple reformulation of the standard event-study approach described and illustrated with artificially constructed data in this paper overcomes the limitations of conventional event-study analyses.