How best to nudge taxpayers? The impact of message simplification and descriptive social norms on payment rates in a central London local authority

Behavioral insights or nudges have yielded great benefits for today’s public administrators by improving the quality of official messages and increasing revenue flows. In the absence of a large number of studies suitable for meta-analysis, less is known about the external validity of these interventions, their range of impact, and the exact matching of the behavioral cue to the client group and context. Factorial designs and repeated interventions, as in the study reported in this article, can add insight through respectively comparing interventions and analyzing their impacts over time. This randomized controlled trial tests whether simplification and/or a descriptive social norm can increase payment of local taxes in a central London local authority. In the first wave, a factorial design on a targeted group of residents, simplification increased the number of people paying by four percentage points, whereas the social norm did not change behavior. In wave two of the study, which was carried out across all households, the descriptive social norm backfired, reducing the rate of payment. The heterogeneous nature of the target population and the exact wording of the social norm are discussed as possible reasons for these results.