Illegal garbage disposals are a persistent urban problem, resulting in high clean-up costs, and nuisance and decreased satisfaction with the neighborhood among residents. We compared three adjacent city-areas in Rotterdam in the Netherlands which, for 2 weeks, either: (1) no action to decrease illegal garbage disposals was taken; (2) standard door-to-door canvassing was carried out; or (3) door-to-door canvassing was enriched with several nudges, most importantly a commitment-nudge. The nudge treatment proved highly effective, reducing illegal disposals at post-test and follow-up (2 months later) with two-thirds, resulting in a very large effect size (d = 2.60). At post-test, standard door-to-door canvassing did not differ from the control treatment, but at follow-up results were comparable to the nudging-treatment. This could, however, be due to spill-over effects. Using a commitment nudge thus proved highly effective in decreasing illegal garbage disposals, however, effects might be specific to neighborhoods with strong social cohesion.
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