Diffusion of Responsibility and Restaurant Tipping: Cheaper by the Bunch

The amount tipped by 396 groups of restaurant diners was a function of the number of people eating together as well as the size of the bill. One-third of the variability in tipping was explained by the norm that tip should equal 15% of bill. In addition, consistent with a new theory of division of responsibility, variation around this norm was an inverse power function of group size, specifically, 18%/N' 22 .