Haggag was able to compare the tips from two cab companies, one of which offered 15, 20, and 25 percent tip suggestions, whereas the other had defaults of 20, 25, and 30 percent. On balance, the screen with the relatively higher default tips significantly increased drivers’ earnings, because they increased the average tip. But interestingly, they also provoked an increase in the number of riders who offered no tip at all.
