Law enforcement officials and leaders can now potentially predict and prepare for mass shootings in schools and bars across the United States.
Although the risk of a mass shooting is low nationwide, researchers estimate that as many as 722 incidents could occur in a single year, with some states, such as California, and locations, such as an office building, more likely to experience one incident.
Calculating the number of mass shootings and their victims is difficult because there is no universally accepted definition of a mass shooting.
However, researchers at Iowa State University analyzed mass shootings from two sources to determine the likelihood of them occurring in certain states and locations.
In one model, the team looked at data from 1966 to 2020 cataloged in The Violence Project database, which defined a mass shooting as an incident in which four or more victims, not including the shooter, were killed by a firearm in a public place.
The organization has recorded 190 mass shootings committed by 194 people between 1966 and 2020, the period for which it keeps data. Since the 1970s, the number of mass shootings, according to its definition, has increased by one every ten years.
Researchers used this data, along with available historical data on mass shootings, to estimate the risk of an incident occurring nationwide, in each state, and at a specific location, such as an office building, school, place of worship, a private home, and a college or university.
While the risk of a mass shooting is low nationwide, some states and locations are more likely to experience one, according to the study from researchers at the University of Iowa.
Researchers at Iowa State University analyzed mass shootings from 1966 to 2020 from The Violence Project database
The study It is estimated that there will be an average of six mass shootings per year in the US, with a 95 percent chance that between two and twelve will occur.
At a school, the chance of a mass shooting is about 0.08 percent.
The researchers also applied their method to a second dataset from The Gun Archive, which uses the expanded definition of a mass shooting, in which four or more people are shot, injured or killed in a public or private location.
Based on this definition, the expected number of mass shootings was 639, with a 95 percent chance that between 567 and 722 events would occur.
The Gun Violence Archive has recorded 537 mass shootings so far in 2023, according to the definition.
When researchers analyzed state-level data based on The Violence Project’s definition, those with the largest populations — California, Texas, Florida, New York and Pennsylvania — were all at the greatest risk of mass shootings.
Researchers then assessed the risk in several locations in the state with the most mass shootings, California, and a state that has never experienced a mass shooting, Iowa.
The annual chance of a mass shooting in Iowa is about 0.06 percent. In California, it’s 0.5 percent, according to one of the models researchers use based on a state’s population.
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The most likely location for a mass shooting in the US is a workplace, with a 0.3 percent chance. It is also the most likely location in California and Iowa, with a probability of about 0.2 percent and 0.02 percent respectively.
While the chance of a mass shooting in a kindergarten through 12th grade is about 0.08 percent nationally, it is lower in California, at 0.05 percent, and nearly zero in Iowa.
“These probabilities suggest that the risk of a mass shooting at a specific location, such as a high school, is extremely low, regardless of state,” researchers said.
“The media attention and tragedy inherent in a school shooting may have caused the American public to overestimate the risk.”
The place least likely to have a mass shooting in the U.S. is a government building or place of social importance, at 0.03 percent. It is also the least likely location in both California and Iowa, at about 0.03 percent and almost zero percent, respectively.
Researchers hope that by providing a more realistic risk assessment of the chances of a mass shooting at a specific location, it will help inform how decision makers can mitigate risk and plan for an incident.
“An organization doesn’t know if one of its locations will be one of the unfortunate locations where a gunman opens fire.
“Assessing the likelihood of a mass shooting at a location can help decision makers understand the risk of a mass shooting,” researchers wrote.
‘A statistical analysis of the chances of a mass shooting provides a more realistic risk assessment than you might conclude based on the attention and media that mass shootings generate.
Decision makers can use this knowledge to make better-informed decisions and trade-offs between mitigating the risk of a mass shooting at their location and other priorities, including other low-probability, high-consequence events.”