Have you ever promised your kids pizza if they behave or do well on a test? Well it doesn't stop working just because you grow up.

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A researcher at Duke University wanted to find out what would motivate people to work harder: a small bonus, props from their boss, or free pizza. Pizza did surprisingly well.

He did the study at a factory in Israel that makes computer chips and sent three emails to three different groups of workers every day for a week. One said they'd get free pizza if they met a certain goal by the end of the day, another said they'd get a compliment from their boss, and the third one said they'd get a $30 bonus.

On day one, the employees who got pizza did more work than anyone. It increased productivity by 6.7%, just edging out a compliment from the boss at 6.6%.

For some reason, a $30 bonus actually made people do less work. They were about 5% more productive on the first day, but did 13% less work than normal on day two, and 6.5% less over the course of the week.

A compliment from the boss ended up having the biggest impact over the course of the entire week, and pizza was a close second.

Read more at New York Magazine.