In a recent study, Dan Ariely discovered something that college students have understood all along—the power of pizza. 

Ariely—James B. Duke professor of psychology and behavioral economics—conducted a study which found that receiving free pizza vouchers or compliments from one’s boss increased productivity in the workplace, while receiving a $30 cash bonus decreased it. The full study is recounted in his new book, “Payoff: The Hidden Logic That Shapes Our Motivations,” which is scheduled to be released Nov. 15.

“We need to start saying to ourselves that simple motivation is very hard to buy,” Ariely said.

The study offered employees at an Intel semiconductor factory in Israel one of three messages promising a reward and then evaluated the messages’ effects on daily and weekly productivity. Every fourth employee received no message, representing the control group.

The three motivators offered by Ariely were a free pizza voucher, a compliment from the boss and a cash bonus. He found that the cash bonus was the only variable resulting in a net loss in productivity—with a 6.5 percent decrease at the close of experimentation—making it worse than providing no incentive at all.

The complimentary text from the boss just barely edged out the pizza voucher as the most motivating variable, Ariely said. He pointed out that he believes the pizza variable would have finished first had he been able to use real pizza in substitution for the voucher, due to the reward of having free pizza delivered directly to employees’ doors.

“We wanted to send people real pizza straight to their homes, so that they could be viewed as heroes in the eyes of their families upon our arrival to deliver it,” Ariely said.

Ariely said that if he were to conduct this experiment again, he would have increased the size of the cash reward. If employees were given enough additional cash, they would be more likely to interpret their bosses’ generosity as greater appreciation for their work and would be more productive in turn, he hypothesized.

The study was a product of Ariely’s mission to better understand how to motivate people to improve themselves.

But the moment you cease to give people incentives, the improvement stops, he noted.

“Even if it works in the moment, that doesn’t mean it will work in the long term,” Ariely said. “So we have to be more creative and more thoughtful in our approach.”

Ariely noted that one approach he takes is a de-emphasis on grades in his class. He said that students’ desires to know exactly what will be on the exam, while perhaps leading to better grades, also undermines the learning process.

In order to understand exactly how administering grades affects classroom performance, it will be necessary for future studies to categorize them as either intrinsic or extrinsic motivators—or whether they are more like compliments or money—Ariely explained.

As an instructor of one of this year’s new Spring Breakthrough sessions—special classes to be held over Spring Break that will not give out grades—Ariely noted that he is excited for the change in grading processes.

“I look forward to teaching in a manner in which there is no grade and no one is thinking about rewards on the other end,” he said.