Servers take note: the smaller the bill, the bigger the tip. In a bit of economic irrationality, big dollar meals don't bring in bring in bigger gratuities. This behavior--known as the magnitude effect--happens whether the service was good or bad.
After looking at nearly 1,000 tips given to waiters, cab drivers and hairstylists, author Leonard Green, lead author and psychologist at Washington University in Saint Louis, found that the standard rules of microeconomics breakdown when the bill is below $50. If we were automatons, perfectly subscribed to the laws of economics, everyone would always tip the same, say 15 percent.
"Percentage-wise you give less on a $150 bill than you do on $20 bill," says Green. As the check gets smaller, he argues that more psychology--and less arithmetic--factors into what makes a tip "fair". He chalks up most of the magnitude effect to patrons financially expressing their thanks for service--be it a cab ride, hair cut or a drink. "It is payment for them just being there," he explains.