Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

In the United States, there are limited national gun laws, with significant variability between individual states. Previously studies have documented an association between permissive statewide laws and higher levels of gun homicide and suicide. However, there has not been significant research into the varying state gun laws on mass shootings. In this cross-sectional time series using from 1998 to 2015, researchers examined annual ratings of states in terms of the permissiveness of their gun laws (scale: 0 to 100), taken from a reference guide for gun owners, as well as gun ownership in the state, and the incidence of mass shootings, defined as an event where four or more people were killed with a firearm. A regression analysis showed that, for a 10-unit increase in state gun law permissiveness, there was a significantly higher rate of mass shootings (11.5%, 95% CI 4.2% to 19.3%, p=0.002). Additionally, significantly higher rates of mass shootings were found with a 10% increase in gun ownership (35.1%, 95% CI 12.7 to 62.7%, p=0.001). This study therefore shows that more permissive gun laws and increased gun ownership are associated with an increase in mass shooting incidence.

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