How Long Do Treatment Effects Last? Persistence and Durability of a Descriptive Norms Intervention's Effect on Energy Conservation

Behavioral decision research has profoundly changed our understanding of decision-making. Recent research has begun to explore how behavioral insights can influence behavior in the world, at scale. This work often involves field experiments studying outcomes over short time windows. We study a descriptive social norms intervention's impact on household energy usage continuously over 39 to 49 months. Our two field experiments (N=155,000 households) each have three conditions: untreated control, continued treatment, and treatment that is subsequently discontinued. We find that continued treatment reduces energy usage over the entire period ("durability"). Further, after treatment is discontinued, a sizable energy use reduction persists ("persistence"). Finally, continued treatment generates a greater impact over time than discontinued treatment, showing that continued treatment exerts incremental influence on behavior over and above persistence. We discuss implications, describe how long-term persistence can occur, and argue that future behavioral decision research should address long-term effects of interventions.