In the United States, there’s much debate over whether gun-related legislation can diminish the likelihood of mass shootings. New research from Harvard Business School turns the question on its head: Do mass shootings lead to more gun-related legislation?
The answer is yes, with an important twist. In states with Republican-controlled legislatures, mass shootings lead to a significant increase in the number of laws that loosen gun restrictions. That’s one of several key findings in the study “The Impact of Mass Shootings on Gun Policy,” co-authored by Michael Luca, Deepak Malhotra, and Christopher Poliquin.
“It would take approximately 66 people dying in individual gun homicide incidents to have as much impact on bills introduced as each person who dies in a mass shooting”
The researchers constructed a dataset of all gun-related legislation and mass shootings in the United States from 1989 to 2014, using data from LexisNexis, the Mass Shootings in America (MSA) project at Stanford University, and a list of shootings created by USA Today. They focused on state rather than Federal regulations, as state governments are the primary regulators of firearms.
For the purposes of the research, they defined a mass shooting as an incident in which four or more people, other than the shooter(s), are unlawfully fatally shot in a single incident not related to gangs, drugs, organized crime, or domestic disputes. “In other words, we focus on the types of random shootings that happen too often in the United States,” says Luca, an assistant professor in the Negotiation, Organizations & Markets unit at HBS.
Using the combined dataset of shootings and bills, the researchers employed a “difference-in-differences” statistical methodology. Their study examined how legislation changed in a state the year after a mass shooting; they used states that did not have shootings as a control group, and controlled for more than 30 other economic and demographic variables that might plausibly impact the proposal or enactment of legislation.
Here’s what they found:
- Of the roughly 30,000 annual gun deaths in the United States, roughly 56 percent are suicides, 40 percent are homicides, and 4 percent are accidents or “incidents of undetermined intent.”
- On average, fewer than 100 gun deaths occur in mass shootings annually. However, while mass shootings account for only 0.3 percent of all gun deaths in the United States, they have a huge effect on policy makers relative to other homicides. “It would take approximately 66 people dying in individual gun homicide incidents to have as much impact on bills introduced as each person who dies in a mass shooting,” the researchers write.
- A single mass shooting in a state leads to a 15 percent increase in the number of gun-related bills introduced in that state’s legislature the year following the shooting. This effect holds true regardless of which political party is in control.
- In terms of laws that are actually enacted, the impact of mass shootings depends on which party is in power. In states with Republican-controlled legislatures, a mass shooting increased the number of enacted laws that loosen gun restrictions by 75 percent. In Democrat-controlled legislatures, mass shootings have no statistically significant effect on laws enacted.
- Between 1990 and 2014, there were 20,409 firearm-related bills proposed in state legislatures across the country. Of the proposals, 3,199 were passed into law, including those that might tighten restrictions, loosen restrictions, do both, or neither.
As an academic institution, Harvard Business School is unusual in that it independently funds almost all of the research conducted by its faculty and doctoral students. That’s notable in the case of this study, considering that in 1996, the US government froze, in large part, federally-funded research on gun violence. That year, Congress pushed through a rider in an annual appropriations bill that prohibited the Center for Disease Control from conducting research “to advocate or promote gun control.” Since then, the legislation often has been interpreted as a prohibition on any federally-funded gun violence research, as explained in the Journal of the American Medical Association article “Silencing the Silence on Gun Research.”
“Lack of evidence on the types of policies that are most effective is one potential reason that voters and political parties can’t even agree on which laws they should target, and whether to loosen or tighten them,” says Malhotra, the Eli Goldston Professor of Business Administration at HBS. “We hope to see more research on both the causes and consequences of gun violence.”
More broadly, “The Impact of Mass Shootings on Gun Policy” raises the general question of what factors drive policy changes—and what factors don’t. “Our findings suggest that while much attention has been rightfully devoted to understanding the impact of policy, there is a lot to be learned from exploring the determinants of policy change as well,” they write. “We find that even random and infrequent events that account for a relatively small portion of total societal harm in a domain might nonetheless be crucial levers for policy consideration and change.”
“While it’s good that policymakers are thinking about gun policies at least some of the time, it would be nice to see more responses to all types of shootings, and a more data-driven approach to policymaking that might elucidate whether the changes in policy are making things better or worse,” Luca says.
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