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Another reason to hate daylight saving time: More assaults

Penn researchers found the assault rate in Philadelphia and other major cities was higher on the Monday after daylight saving time ended, compared with the following Monday.


Those who are weary of early morning darkness may welcome the end of daylight saving time on Sunday, Nov. 5, when most of the nation turns the clock back an hour. But keep a cool head the next day.

A new University of Pennsylvania study finds that the end of daylight saving each fall is linked to a short-term increase in the assault rate.

The authors analyzed crime data from Philadelphia, Chicago, Los Angeles, and New York from 2001 through 2014. They included aggravated assault, which meant the attacker had a weapon or the victim suffered severe injury, as well as simple assault.

The average assault rate was 2.8 percent higher on the Monday immediately following the end of daylight saving time when compared with the Monday a week later.

But in the spring, when clocks are turned forward an hour, the assault rate was 2.9 percent lower the next day than it was a week later, the authors reported in the Journal of Experimental Criminology.

Statistical tests suggested that the springtime decrease in assault was more likely linked to the clock shift, whereas the fall increase in assault could have been due to other factors, said Greg Ridgeway, one of the authors and an associate professor of criminology and statistics at Penn.

Still, the findings came as somewhat of a surprise, as people have an extra hour to sleep after the fall clock shift, whereas they lose an hour in the spring. Past research has linked poor sleep with antisocial behavior and aggression, said fellow author Adrian Raine, a Penn professor of criminology, psychiatry, and psychology.

"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 said. "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."

Fed up with the twice-a-year clock shifts, lawmakers in some states have sought to end the practice, most recently in Massachusetts and Maine.

Whether or not that would affect assault rates in the short term, previous research has tied daylight saving to a variety of other ills.

At the start of daylight saving in the spring, there are more car accidents and workplace injuries, studies have found.