Effect of niceness on tipping - This American Life on NPR
A sociological experiment indicating that a server's manner has little or no influence on tipping.
I thought it interesting that the servers had the belief that the diner tips according to habit more than anything else. Goes along with other research that has shown tipping and service levels tend not to correlate. So in effect it's really about how people are conditioned, peer group pressure etc rather than the actual service.
It ties back to another thread that debated whether it was right to reduce a tips for poor service when the restaurant comped some dishes as compensation. The consensus seemed to be not to significantly reduce the tip percentage because the restaurant had already reduced the vale of the tip by comping some dishes so a lower overall bill to tip on.
I thought that was interesting as it contradicts the mantra about tipping based on service, more for good less for bad. It struck me that despite getting bad service people just couldn't bring themselves to lower the tip - they are habituated to a certain tip level. And many posters used all sorts of logic to justify their "need" to tip according to their habits.
I find it a fascinating subject, especially the amount of traffic it generates about something that is so common and apparently simply understood by all diners. It's really interesting to read all the post-hoc logical justification for something that is just a habit.