Some of the wonderful folks at UBC-DIBS and BEAR have partnered together to create a “A meta-analytic cognitive framework of nudge and sludge”. Here’s more from authors Yu Luo, Andrew Li, Dilip Soman, and Jiaying Zhao:
“A nudge is designed to facilitate actions by minimizing friction, while a sludge is an intervention that inhibits actions by increasing friction. We organize these interventions along six cognitive processes: attention, perception, memory, effort, intrinsic motivation and extrinsic motivation. In addition, we conduct a meta-analysis of field experiments to examine the effect size of these interventions targeting each cognitive process. Our findings demonstrate that interventions changing effort are more effective than interventions changing intrinsic motivation, and nudge and sludge interventions had similar effect sizes.” [edited for brevity]