6 Mar
2025
No Sunk Cost Effects in Health Behavior

Previous evidence on the sunk cost fallacy primarily comes from laboratory or online experiments in which the sunk cost consists of a single upfront payment. In this paper, we study sunk cost effects in a highly relevant field context (exercising), where sunk costs may be dispersed over time and influence habit formation. In particular, we investigate how a (random) two-month discount on the membership fee affects the exercising behavior of new members of a large fitness chain and test whether individuals mentally account for the timing of this discount, i.e., the dispersion of sunk costs over time. The experimental design allows us to exclude any selection into discounted memberships and thereby isolate potential sunk cost effects. Despite a highly powered design, we do not find any evidence of sunk cost effects. These results cast doubt on the relevance of the sunk cost fallacy in the health domain. They also suggest that the common practice of offering discounts on membership fees does not undermine habit formation.