Night Owl
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If you're a night owl, you're probably grouchy if you're awake at 6:30 a.m. Now, research shows that you're also more likely to cheat at that hour. Likewise, early birds face the same dilemma at midnight.

"Even within the same day, a given person could be ethical at one point in time and unethical at another point in time," the authors wrote.

While earlier research indicated that people become more ethical throughout the day, this study also took into account people's natural circadian rhythms over two experiments.

First, participants were paid depending on the number of matrix puzzles they said they solved. The sessions were held in the morning, and night owls were more likely to over-report their numbers.

Next, participants were paid based on the numbers they rolled on dice, in sessions starting at 7 a.m. or midnight. Only the participants could see the numbers rolled, and more money was given for higher numbers. As predicted, night owls reported higher numbers in the morning than they did at night. And early birds reported higher numbers at night than they did in the morning.

"We know that ethical decisions are taxing," study researcher Sunita Sah, a professor of business ethics at the McDonough School of Business at Georgetown University, told American Public Media's Marketplace. "We have limited cognitive resources and less self-control at certain times of the day."

The findings add a layer of complexity to the idea that certain people are either ethical or unethical. Instead, we should schedule tasks around our rhythms.

So if you're a night owl, fill out your expense report in the evening, Sah suggests.