Nudging: To know ‘what works’ you need to know why it works

Nudging is widely portrayed as a purely inductive approach to influencing human behavior. However, this paper argues that to understand ‘what works’ when it comes to nudging, requires practitioners and researchers to properly understand the practical implications of underlying theory. This is argued by showing how the concept of nudge itself stipulates the main boundary condition for the efficacy of nudging as well as calls for consideration of what psychological mechanisms mediate a nudge and its behavioral effects. The implications are then illustrated relative to the intuitively appealing policy application of nudging people into becoming organ donors by changing the default from an opt-out to an opt-in system; and in turn reveals why most practitioners and researchers believe this policy application to be such a bad idea. Finally, the practical implications of theory are formalized into a template for practitioners to use in structuring the behavioral insights they consider as part of a nudge.