Understanding soft commitment: evidence from a field experiment on recycling

Abstract

Taking advantage of a card-scanning system that records individual, real-time data on the use of bio-waste sorting bins, we run a randomized field experiment to analyze the effectiveness of soft commitments in promoting participation in waste sorting. Being given the offer to sign a soft commitment increased participation in waste sorting by 7-8 percentage points (0.22 s.d.). This represents a 23-28% increase relative to the control group of households that participated in the study but were not given the opportunity to sign a soft commitment. This positive effect of the soft commitment operates exclusively through the extensive margin (households start to sort their waste); it does not affect the intensive margin (household adherence to waste sorting). This implies that soft commitments can improve the effectiveness of environmental campaigns in cities or areas where a large part of the population has never participated in waste sorting, while they would have little impact in places where a majority of households have already participated in recycling. We also show that the positive effect of the soft commitment remains constant 35 weeks after being offered. The effect also persists after 36-47 weeks, although its size is reduced by one half.