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PHILADELPHIA — Cities experienced 2.3 more assaults than average on days when hosting presidential campaign rallies for Donald Trump during the lead-up to the 2016 United States Presidential Election, according to a first of its kind study published online today in Epidemiology by researchers in the Perelman School of Medicine at the University of Pennsylvania. Hillary Clinton rallies were not linked to any increase in assaults, they found.

“News media sources reported there were violent incidents at some campaign rallies, but it was difficult to gauge whether there really was a systematic problem, and if so, how many additional assaults were associated with each rally,” said the study’s lead author, Christopher Morrison, PhD, MPH, a fellow in Penn’s Center for Clinical Epidemiology and Biostatistics and an epidemiologist in the Penn Injury Science Center. “To prevent similar violence in the future, it is important to understand the underlying causes of this behavior, perhaps including the role that political rhetoric might play in normalizing or promoting violence.”

Focusing on cities of greater than 200,000 people, the team performed a systematic Google search and found publicly available data for 31 rallies in 22 cities for Trump and 38 rallies in 21 cities for Clinton. Using assault data from police departments in those cities, including aggravated assaults, simple assaults, and/or battery, the team counted assaults on the day of each rally. For comparison, they also counted assaults on corresponding days of the week for four weeks before and four weeks after each rally.

Rallies in the study were defined as open invitation events that occurred after Donald Trump and Hillary Clinton declared their candidacies in spring 2015 and before the U.S. Presidential Election on November 8, 2016, featured a speech by Trump or Clinton, and were not on the same day as a party primary election in the same state as the rally.

The researchers suggest two possible explanations for their findings. First, all additional assaults could have occurred in and around the venues of candidate Trump’s rallies where people invested in the process gathered. This explanation is consistent with news media reports that violence occurred at these specific locations. Second, additional assaults that took place might have occurred elsewhere in the rally cities. Studies informed by theories of social contagion find evidence that emotional states can be transmitted through news reports and digital social media, which could have led to more assaults occurring away from the rally sites. 

The researchers note that Trump rallies were widely broadcast and discussed through news reports and digital social media, such as a  rally in Cedar Rapids, Iowa during which candidate Trump remarked that he would “knock the crap out of” would-be hecklers at the event, and other examples from the non-partisan POLITIFACT.

“This research provides evidence that this increase in assaults is associated with candidate Trump’s rallies leading up to the election,” said senior author Douglas Wiebe, PhD, an associate professor in Epidemiology. “Violent language may have affected the mood and behavior of rally attendees, as well as those exposed to the rally through news reports and social media.”

The researchers added that weather can also influence crime rates, so the team consulted National Oceanic and Atmospheric Administration data for the weather station nearest to each study city to control for temperature and precipitation.

In addition to Morrison, additional Penn authors include Benjamin Ukert, Aimee Palumbo, Sara F Jacoby, and Douglas J Wiebe from Penn, and Beidi Dong from George Mason University.

Penn Medicine is one of the world’s leading academic medical centers, dedicated to the related missions of medical education, biomedical research, excellence in patient care, and community service. The organization consists of the University of Pennsylvania Health System and Penn’s Raymond and Ruth Perelman School of Medicine, founded in 1765 as the nation’s first medical school.

The Perelman School of Medicine is consistently among the nation's top recipients of funding from the National Institutes of Health, with $550 million awarded in the 2022 fiscal year. Home to a proud history of “firsts” in medicine, Penn Medicine teams have pioneered discoveries and innovations that have shaped modern medicine, including recent breakthroughs such as CAR T cell therapy for cancer and the mRNA technology used in COVID-19 vaccines.

The University of Pennsylvania Health System’s patient care facilities stretch from the Susquehanna River in Pennsylvania to the New Jersey shore. These include the Hospital of the University of Pennsylvania, Penn Presbyterian Medical Center, Chester County Hospital, Lancaster General Health, Penn Medicine Princeton Health, and Pennsylvania Hospital—the nation’s first hospital, founded in 1751. Additional facilities and enterprises include Good Shepherd Penn Partners, Penn Medicine at Home, Lancaster Behavioral Health Hospital, and Princeton House Behavioral Health, among others.

Penn Medicine is an $11.1 billion enterprise powered by more than 49,000 talented faculty and staff.

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