(with Maarten Luts, Johannes Spinnewijn, and Teodora Tsankova)
We study the impact of deterrence, tax morale, and simplifying information on tax compliance. We ran five experiments that span the tax process and vary the communication of the tax administration with the universe of taxpayers in Belgium. The results provide a clear picture across the experiments: (i) simplifying communication always increases compliance, (ii) deterrence messages have an additional positive effect, (iii) invoking tax morale is not effective. While machine-learning methods reveal important heterogeneity in treatment effects, tax morale treatments backfire for most taxpayers. They do, however, improve their knowledge and appreciation of public services. We also provide a comprehensive analysis of the dynamics and interactions of the treatment effects within and across tax years. Finally, a discontinuity in enforcement intensity allows us to compare the effect of standard enforcement measures with the effect of simplification treatments, which we find to be far more cost-effective.