When Daylight Saving Time (DST) officially began this year on March 11, we lost an hour of sleep. Much has been studied about long-term effects of sleep deprivation, but fourth-year Penn criminology doctoral student Rebecca Umbach wanted to better understand what happens immediately following such a short-term loss.
Using a large database called the National Incident-Based Reporting System, which tracks the time, date, and details of individual crimes for many cities across the country, supplemented with data from New York, Chicago, Los Angeles, and Philadelphia, she and Penn criminologists Adrian Raine and Greg Ridgeway looked at the Mondays after the start of DST.
They discovered that the overall assault rate dropped by about 3 percent, findings they published in the Journal of Experimental Criminology. This was the opposite of what they had hypothesized—that after a night with an hour less sleep people would become more antagonistic—and counter to what research has already shown happens in other facets of life.
“In the spring, the day after we move into Daylight Saving Time,” says Ridgeway, “there are more car accidents, greater stock market losses, more workplace injury, reduced test scores, and higher suicide rates.”
The findings also differ from research on the long-term effects of getting less sleep. Work by Raine, for example, connected daytime drowsiness at age 15 to violence at age 24.
“Sleep problems have previously been associated with increased antisocial and criminal behavior, so we were surprised to find that increased sleep was associated with increased offending,” Raine says. “This discrepancy is likely due to the fact that 40 to 60 minutes of lost sleep in one night is just not the same as months, or even years, of poor sleep.”
The researchers also looked at the fall time change, when we regain that hour of sleep. Though they found that assaults rose by about 3 percent the next day—a mirror image of the spring findings—they say their supporting evidence here isn’t as robust.
Regardless, it is challenging to explain why these results occurred; Umbach surmises it may relate to internal biases.
“You think, ‘If I don’t get a lot of sleep, I’m going to be cranky and angry.’ You assume that’s the way you would react,” she says. “Your intention is to act more aggressively, but your behavior does not reflect that because you’re tired. You’re too lethargic and sleepy to act.”
Daylight Saving Time made for a logical study subject. For one, research has shown that sleep tends to decrease because of the time switch, as opposed to anticipating the shift and going to bed earlier. Secondly, nearly any other Monday of the year could, in theory, act as a control; to isolate sleep as the explanatory variable—rather than changes in weather or daylight, say—the Penn researchers chose the Monday the week after each time switch.
Though the team doesn’t currently have plans for follow-up research, Raine says anyone who ignores the morning alarm ring might take heed. “Before we hit that snooze button, perhaps we should stop and think. Hit the button and we might end up at least a little grumpier at work, and possibly more aggressive.”
Adrian Raine is a Penn Integrates Knowledge professor and the Richard Perry University Professor of Criminology, Psychiatry, and Psychology in the School of Arts and Sciences and Penn’s Perelman School of Medicine.
Greg Ridgeway is Associate Professor of Criminology and Statistics in the Criminology Department in the School of Arts and Sciences.
Rebecca Umbach is a fourth-year doctoral candidate in the Criminology Department in the School of Arts and Sciences.
