Gun Laws Have Basically No Impact on Mass Shooter Rate

BJ Campbell
Handwaving Freakoutery
11 min readMar 10, 2019

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And the mass shooter rate is fabulously low to begin with.

The media cycle this weekend has landed on a new study published by the BMJ, (archive link) on the connection between state gun laws and rate of mass shooting incidents. It’s been picked up by Vox, Yahoo, and elsewhere. Predictably, this study is being leveraged in our collective social media metabrain to push the idea that more gun laws reduce mass shootings.

The study by Paul Reeping, Bindu Kalesan, and Charles Branas, has couple of real howlers buried in it that we need to talk about, and the conclusions it draws are technically correct but misleading in practice. Let’s look at the study and then speak of what useful conclusions we can draw from it.

The Study

You can find the study, titled “State gun laws, gun ownership, and mass shootings in the US: cross sectional time series,” here. (academic citation: BMJ 2019;364:l542) An archive link is here. I encourage readers to go there, read it, and come back, but here’s a brief summary from their abstract:

Exposure An annual rating between 0 (completely restrictive) and 100 (completely permissive) for the gun laws of all 50 states taken from a reference guide for gun owners traveling between states from 1998 to 2015. Gun ownership was estimated annually as the percentage of suicides committed with firearms in each state.

Main outcome measure Mass shootings were defined as independent events in which four or more people were killed by a firearm. Data from the Federal Bureau of Investigation’s Uniform Crime Reporting System from 1998–2015 were used to calculate annual rates of mass shootings in each state. Mass shooting events and rates were further separated into those where the victims were immediate family members or partners (domestic) and those where the victims had other relationships with the perpetrator (non-domestic).

Results Fully adjusted regression analyses showed that a 10 unit increase in state gun law permissiveness was associated with a significant 11.5% (95% confidence interval 4.2% to 19.3%, P=0.002) higher rate of mass shootings. A 10% increase in state gun ownership was associated with a significant 35.1% (12.7% to 62.7%, P=0.001) higher rate of mass shootings. Partially adjusted regression analyses produced similar results, as did analyses restricted to domestic and non-domestic mass shootings.

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