Plenty of anecdotes abound on the Web from restaurant servers who dread the Sunday after-church lunch crowds — and who even report receiving religious tracts alongside a low tip, or in lieu of one entirely. The stereotype that Christians are lousy tippers was magnified with the excruciating report that a St. Louis-area waitress at an Applebee’s was recently fired for posting a local pastor’s complaint, written on her receipt, about a mandatory 18 percent gratuity for large group: “I give God 10% why do you get 18,” she wrote.

The numbers, such as they exist, don’t quite add up. Christians don’t tip quite as well as Jews or people of no religion, but perhaps surprisingly, no religious or non-religious group on average reports ...