Odi et Amo: A nudge to reduce the consumption of single-use carrier bags

In this article we show that it is possible to reduce carrier bags consumption without imposing additional costs on supermarket customers. To this end, we exploit the fact that people shopping in a certain area are likely to have homogeneous preferences on certain dimensions (e.g., sport teams). We implement a simple treatment in a supermarket in Naples, Italy: whenever a customer of the supermarket buys a single-use carrier bag we donate a small sum to an institution that is likely to be perceived negatively by the customers of the supermarket (an "anti-charity"). Vice versa, whenever a customer does not purchase a bag, we donate the same amount to an association that is likely to be perceived positively by the customers of the supermarket (a "charity"). We measure the impact of the treatment with respect to the previous weeks, the corresponding weeks of the previous year and we look at the persistence of the effect. Our results show that this treatment causes a significant reduction in bags consumption without imposing monetary costs on supermarket customers. Moreover, we show that our nudge can easily be used by regulators at virtually no cost by creating multi-city tournaments. We explain how these tournaments could be arranged.