Our ability to exhibit self-control to avoid cheating or lying is significantly reduced over the course of a day, making us more likely to be dishonest in the afternoon than in the morning, according to findings published in Psychological Science, a journal of the Association for Psychological Science.

“As ethics researchers, we had been running experiments examining various unethical behaviors, such as lying, stealing, and cheating,” researchers Maryam Kouchaki of Harvard University and Isaac Smith of the University of Utah’s David Eccles School of Business explain. “We noticed that experiments conducted in the morning seemed to systematically result in lower instances of unethical behavior.”

This led the researchers to wonder: Is it easier to resist opportunities to lie, cheat, steal, and engage in other unethical behavior in the morning than in the afternoon?

Knowing that self-control can be depleted from a lack of rest and from making repeated decisions, Kouchacki and Smith wanted to examine whether normal activities during the day would be enough to deplete self-control and increase dishonest behavior.

In two experiments, college-age participants were shown various patterns of dots on a computer. For each pattern, they were asked to identify whether more dots were displayed on the left or right side of the screen. Importantly, participants were not given money for getting correct answers, but were instead given money based on which side of the screen they determined had more dots; they were paid 10 times the amount for selecting the right over the left. Participants therefore had a financial incentive to select the right, even if there were unmistakably more dots on the left, which would be a case of clear cheating.

In line with the hypothesis, participants tested between 8:00 am and 12:00 pm were less likely to cheat than those tested between 12:00 pm and 6:00pm — a phenomenon the researchers call the “morning morality effect.”

They also tested participants’ moral awareness in both the morning and afternoon. After presenting them with word fragments such as “_ _RAL” and “E_ _ _ C_ _” the morning participants were more likely to form the words “moral” and “ethical,” whereas the afternoon participants tended to form the words “coral” and “effects,” lending further support to the morning morality effect.

The researchers found the same pattern of results when they tested a sample of online participants from across the United States. Participants were more likely to send a dishonest message to a virtual partner or to report having solved an unsolvable number-matching problem in the afternoon, compared to the morning.

They also discovered that the extent to which people behave unethically without feeling guilt or distress — known as moral disengagement — made a difference in how strong the morning morality effect was. Those participants with a higher propensity to morally disengage were likely to cheat in both the morning and the afternoon. But people who had a lower propensity to morally disengage — those who might be expected to be more ethical in general — were honest in the morning, but less so in the afternoon.

“Unfortunately, the most honest people, such as those less likely to morally disengage, may be the most susceptible to the negative consequences associated with the morning morality effect,” the researchers write. “Our findings suggest that mere time of day can lead to a systematic failure of good people to act morally.”

Kouchacki, a post-doctoral research fellow at Harvard University’s Edmond J. Safra Center for Ethics, completed her doctoral studies at the University of Utah, where Smith is a current doctoral student. They note that their research results could have implications for organizations or businesses trying to reduce unethical behavior.

“For instance, organizations may need to be more vigilant about combating the unethical behavior of customers or employees in the afternoon than in the morning,” the researchers explain. “Whether you are personally trying to manage your own temptations, or you are a parent, teacher, or leader worried about the unethical behavior of others, our research suggests that it can be important to take something as seemingly mundane as the time of day into account.”