Every time I present a nudge result, someone asks the same question: is a 3% reduction in electricity use important? My view is that an effect size only becomes economically meaningful when you ask what it would have cost to move behavior using standard tools, such as a tax or a subsidy. That's what Matthias Rodemeier, Sutanuka Roy, Gregory Sun and I do in a new study across five markets (electricity, water, cigarettes, alcohol, flu shots). The numbers are bigger than I expected: an average electricity nudge does the work of an 11% tax; water, 17%, cigarettes, 28%, and alcohol, 34%. Flu shots? Roughly a 100% subsidy. That means you must make the vaccine free to match it. Nudges are also more cost-effective than price instruments in all five markets. But here's the part that changed how I think about this: cost-effectiveness does not give you the welfare ranking and scale plays a role.  You can find out why in the paper, available here: ideas.repec.org/p/ces/ceswps…