I want to get this out of the way before I get into the meat of this article. I’m going to be discussing an academically fascinating study, that relates to gun laws. In this article, I may tread close to the line of politics, though I will strive to the utmost not to. Our managing editor, Pete, suggested that I do this write-up, and I eagerly accepted. During my writing process, the article has been subject to close editorial oversight. I want to inform you, my readers, without stepping over the line into politics. I believe I succeeded.

So, with that in mind, lets jump right in. What exactly am I talking about? Doctor Michael Siegel of Boston University and a team of four others; Molly Pahn, Ziming Xuan, Eric Fleegler, and David Hemenway, conducted an evaluation study of 10 different state-level gun laws over a 26 year period from 1991 to 2016. They made 1222 “observations”, 47 states times 26 years. The reason they only evaluated 47 states was that three, North Dakota, Vermont, and Wyoming, did not have a complete set of data for those 26 years. The authors, accordingly, did not include these states in the study.

State Gun Laws

As I mentioned, Dr. Siegel et. al. evaluated 10 different state-level gun laws for effectiveness. In no particular order, they were

1. Universal Background Checks. Individuals must undergo a  background check to purchase any type of firearm, either at the point of purchase or through a license/permit application.
2. Violent Misdemeanor Laws. Prohibition of handgun ownership for individuals convicted of a violent misdemeanor punishable by less than 1 year in prison.
3. Handgun Possession Age Restriction. No possession of handguns until age 21.
4. Shall-Issue Laws. The licensing authority must issue a conceal-carry permit to an applicant unless they meet pre-established disqualifying factors.
5. Permitless Carry. Also known as Constitutional Carry. There is no requirement for a permit to conceal and carry a handgun in public.
6. Trafficking Prohibited. Also known as a straw purchase ban. No person may purchase a firearm with the intent to sell to a prohibited person.
7. Junk Gun Ban. Also known as a ban on “Saturday night specials.” A law prohibiting the sale of handguns meeting specific criteria such as drop testing, melting point testing, certain safety features, and/or an approved handguns roster.
8. Stand Your Ground. There is no duty to retreat from an attack in a public place where you have the right to be.
9. Assault Weapons Ban. A ban on “assault weapons,” usually patterned after the Federal Assault Weapons Ban of 1994-2004, which banned various cosmetic features on rifles.
10. Large Capacity Magazine Ban. Exactly what it sounds like, a ban on the sale (though not necessarily possession) of “large” (standard) capacity magazines.

Data Analysis

Before the findings, a few quick notes. First, the study excluded homicides due to legal intervention (i.e., death by cop), which accounted for 1% of firearm deaths, unintentional firearm fatalities which accounted for 2.5% of firearm deaths, and fatalities of undetermined intent which accounted for 1% of firearm deaths. They also controlled for 12 variables that might have skewed the data. These variables were: (1) the percent of the population that is black; (2) the percent of population ages 15–29 that is male; (3) per capita law enforcement officers; (4) the violent crime rate (excluding homicide); (5) the divorce rate; (6) the unemployment rate; (7) the poverty rate; (8) per capita alcohol consumption; (9) the incarceration rate; (10) population density; (11) log of population; and (12) household gun ownership percentage.

Interestingly, mostly to statistics nerds, the authors tweaked the most common (and somewhat controversial) estimate for household gun ownership. Most authors use the ratio of firearm suicides to all suicides as a proxy for household firearm ownership. This proxy has a good (r=0.8) correlation with the results of surveys on gun ownership. The authors incorporated the state’s hunting license rate into this ratio and found an improved correlation (r=0.95).

The Findings

In as clear of English as I can put it, this is what the authors found. Firstly, universal background checks correlated with a 14.9% reduction in overall homicide rates. Secondly, violent misdemeanor laws were correlated with an 18.1% reduction in homicide rates. Thirdly, shall-issue laws were associated with a 9% increase in homicide rates. This third finding, a 9% increase in homicide rates correlating with shall-issue laws, is the weakest of the three in terms of supporting evidence from other publications. Numerous other studies have both supported and disagreed with the notion that shall-issue increases homicide rates, something the authors mention in the paper.

Further, it’s interesting what the authors did not find. The authors found no correlation between overall homicide rates and any other law in the study. Not assault weapons bans, or magazine-capacity limits were shown to have a measurable correlation with homicide rates.

Interestingly, the study found that bans on “junk guns” were associated with slightly lower (6.4%) suicide rates, and permitless carry laws with modestly higher (5.1%) suicide rates. Both of those findings, however, failed the author’s falsification test. A falsification test is an effort to make sure that there isn’t some external X factor influencing the data. Both findings were shown to have a similar correlation with the non-firearm suicide rate, not just the overall suicide rate. Since these failed the falsification test, they were excluded from the final conclusion.

Strengths and Limitations

The study has many strengths that lend credence to its findings. First, it clearly defines each assessed law, with attention to its provisions, scope, and exceptions. Secondly, the analysis used a difference-in-differences analysis model. A difference-in-differences analysis evaluates both test and control groups when you cannot randomize participants in either group. Since the populations were those of entire states in past years, obviously randomization was impossible.

However, the study also has limitations. First and foremost, the study begins in 1991 and ends in 2016. Therefore it covers several changes in Federal law (most notably the 1994 AWB and its expiration). Secondly, the authors included as one of their laws being evaluated a straw-purchase ban. This ban is Federal law, as well as in some cases a state law. This already existing prohibition may explain why that particular intervention failed to show a measurable impact.

Conclusion

To wrap things up, I will borrow the author’s words. “Further research on the impact of state firearm laws is necessary to assess causality and should rely upon detailed definitions of each law.” This study is a strong indicator that some things work, and other things don’t. It has both its limitations and its strengths. Hopefully, we will see future research of this type, to better inform both the public and our elected officials.

A Note on the Source

An outline of the article being analyzed can be found here. Doctor Siegel was kind enough to furnish me with a copy of his research free of charge, so I do not have a link to the full study that I can provide.