With an hour of the start of this month's historic mass shooting at the Route 99 Harvest Festival, the Las Vegas Metropolitan Police Department tweeted about it three times, warning that there were reports of an “active shooter near/around Mandalay Bay casino,” directing journalists to a staging area where information would be disseminated, and informing motorists that a core portion of the Las Vegas Strip was closed to traffic.

The tweets kept coming in the late hours: Cops asked witnesses and folks monitoring emergency radio traffic not to reveal their “tactical positions.” And they informed the world that “one suspect is down.” The broadcasting was exemplary, says UC Irvine researcher Nickolas M. Jones. “Frequent communication from emergency management officials is a necessary ingredient,” he says.

Jones is the lead author on a new study, “Distress and rumor exposure on social media during a campus lockdown,” about how officials communicate with people during emergencies. It was published online this week in the Proceedings of the National Academy of Sciences.

Southern California researchers looked at the hours and days after a recent “active shooter event” on an unnamed college campus and measured social media communication and the stress levels of 4,000 students who dialed up Twitter during a two-hour lockdown at school.

A few conclusions resulted: Authorities need to blast out frequent updates as soon as they can. And they should monitor social media in order to dispel dangerous rumors. “When danger is imminent and official information is disseminated inconsistently, public anxiety is elevated,” according to a summary.

“It's really important that they release messaging that will mitigate uncertainty and anxiety,” Jones says. “We think they should monitor social media for rumors and take them head on when they crop up.”

The Los Angeles Police Department has turned increasingly to its social media channels to inform the public when major emergencies take place.

“The LAPD is aware that in the absence of relevant, timely, critical and accurate information, a crisis or emergency situation can paralyze a community,” spokesman Josh Rubenstein said via email. “That is why the department is committed to finding new ways to relay fast and factual information to the public during these situations. We have a social media team that is responsible for using various platforms to reach Angelenos. It is important to note, however, that the speed at which the public demands information often comes at the price of accuracy, and that is a very delicate balance we are always trying to reach in our Public Communications Group.”

The flip side of the study's recommendations is that folks who rely most on social media tend to register the most stress during emergencies, according to the study. “Higher acute stress was reported by heavy social media users who trusted social media for critical updates,” according to the research abstract.

That's why, researchers argue, it's so important to use accurate information to calm nerves. Rumors thrive in the absence of good information and frequent updates, Jones says.

The UC Irvine paper cites a mass shooting last year at a McDonald's in Munich. Rumors abounded that multiple shooters were opening fire across the city. Police used social media channels to “tell people to stay home and stop speculating,” Jones says. “We believe had police not done that, those rumors would have continued to fill the information void.”

In emergencies, rumors can be fatal, and misinformation can inspire callers to clog 911 lines. These rumors can also push people into harm's way because the location of the danger is unknown. If people are reacting to rumors that send them into dangerous situations, Jones says, officials need to quickly let the public know “police are on it.”

“When you're in an ambiguous, dangerous situation you're psychologically activated,” he says. “That's why people seek information. They want to alleviate the discomfort associated with uncertainty.”

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