"People were more likely to return a wallet when it contained a higher amount of money," Cohn says. "At first we almost couldn't believe it and told him to triple the amount of money in the wallet. But yet again we found the same puzzling finding."
The researchers decided to do the experiment on a much larger scale. They put together a team that dropped off more than 17,000 "lost" wallets in 40 countries over the course of more than two years.
All the wallets were about the same — a small clear case holding a few business cards, a grocery list in the local language, and a key. Some contained no money and some held the equivalent of about $13. Research assistants turned them in at the kinds of places people would typically bring a wallet they found on the ground — police stations, hotels, post offices and theaters.