Law enforcement officials and leaders may now be able to predict and prepare for mass shootings in places like schools and bars across the United States.
While the risk of a mass shooting is low nationwide, researchers estimate that up to 722 incidents could occur in a year, with such an incident being more likely in some states such as California and in locations such as an office building.
Calculating the number of mass shootings and their victims is difficult because there is no consistent definition of a mass shooting.
However, researchers at Iowa State University analyzed mass shootings from two sources to determine the likelihood that mass shootings would occur in specific states and locations.
In one model, the team examined data from 1966 to 2020 cataloged in the Violence Project database. These defined a mass shooting as an incident with four or more victims, not including the shooter, who was killed by a firearm in a public place.
The organization recorded 190 mass shootings committed by 194 people between 1966 and 2020, the period over which it stores data. Since the 1970s, the number of mass shootings has risen by one every ten years.
The researchers used this data, along with available historical data on mass shootings, to estimate the risk of an incident occurring across the country, in each state, and at a specific location, such as an office building, a school, a place of worship, a private residence, or a college University.
While the risk of a mass shooting is low nationwide, the likelihood of a mass shooting occurring is higher in some states and localities, according to the study by 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 estimated that mass shootings would occur an average of six times per year in the United States, with a 95 percent chance that it would occur between two and 12.
In a school, the probability 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 when four or more people are shot, injured or killed in a public or private place.
Based on this definition, the projected number of mass shootings was 639, with a 95 percent chance that between 567 and 722 events would occur.
According to its definition, the Gun Violence Archive has recorded 537 mass shootings so far in 2023.
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 greatest risk of becoming victims of mass shootings.
The researchers then estimated the risk in different locations in the state with the most mass shootings, California, and in a state that has never had a mass shooting, Iowa.
The annual chance of a mass shooting in Iowa is about 0.06 percent. In California it is 0.5 percent, according to a model that researchers use based on a state’s population.
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The place with the highest probability of a mass shooting in the United States 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 probability of a mass shooting in a kindergarten through 12th grade school is about 0.08 percent nationally, it is lower at 0.05 percent in California and almost zero in Iowa.
“These probabilities suggest that the risk of a mass shooting at a given location, such as a high school, is extremely low, regardless of state,” researchers said.
“The media attention and tragic nature of a school shooting may have led the American public to overestimate the risk.”
The place least likely to have a mass shooting in the United States is a government building or a place of civic significance (0.03 percent). It is also the least likely location in both California and Iowa, at about 0.03 percent and near zero percent, respectively.
The researchers hope that by providing a more realistic risk assessment of the likelihood of a mass shooting in a given location, it can help decision-makers mitigate the risk and plan for an incident.
“An organization doesn’t know whether one of its locations will be one of the unfortunate places where a shooter opens fire.”
“Assessing the likelihood of a mass shooting in a location can help decision makers understand the risk of a mass shooting,” the researchers wrote.
“A statistical analysis of the likelihood of a mass shooting provides a more realistic assessment of risk than what one might conclude based on the attention and media that mass shootings generate.”
Decision makers can use this knowledge to make more informed decisions and weigh trade-offs between mitigating the risk of a mass shooting at their location and other priorities, including other low-probability, high-consequence events.”