In 2016, DUL sent half of Duke’s six thousand undergraduates a survey and told them that if they completed and returned it, they’d be entered into a raffle for a $75 gift card. The other three thousand students also received an email with the survey. But the accompanying rules were different. Everybody would be entered in a raffle for a $75 gift card. But if the organizers drew someone’s name and that person had not completed the survey, he would be ineligible for the prize and the organizers would select another name. Which approach yielded the most survey responses? It wasn’t even close.
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