Monday, March 12, 2018

The Distressingly Weak Lessons of Research on Gun Control

If you want to know what actual research on the effects of various gun control policies have to say, the RAND Corporation has your back. It has published a lengthy reports: "The Science of Gun Policy:  A Critical Synthesis of Research Evidence on the Effects of Gun Policies in the United States," by a team of 17 researchers led by Andrew R. Morral. A smaller group led by Morral also published  "The Magnitude and Sources of Disagreement Among Gun Policy Experts."  And there's also a nice accessible website with a summary of results and links to these more detailed studies. They write: 
The 13 classes of gun policies considered in this research are as follows:

1. background checks
2. bans on the sale of assault weapons and high-capacity magazines
3. stand-your-ground laws
4. prohibitions associated with mental illness
5. lost or stolen firearm reporting requirements
6. licensing and permitting requirements
7. firearm sales reporting and recording requirements
8. child-access prevention laws
9. surrender of firearms by prohibited possessors
10. minimum age requirements
11. concealed-carry laws
12. waiting periods
13. gun-free zones.

The eight outcomes considered in this research are

1. suicide
2. violent crime
3. unintentional injuries and deaths
4. mass shootings
5. officer-involved shootings
6. defensive gun use
7. hunting and recreation
8. gun industry.
They focus on high-quality studies published since 2003. They write:
"[W]e produced research syntheses that describe the quality and findings of the best available scientific evidence. Each synthesis defines the class of policies being considered; presents and rates the available evidence; and describes what conclusions, if any, can be drawn about the policy’s effects on outcomes. In many cases, we were unable to identify any research that met our criteria for considering a study as providing minimally persuasive evidence for a policy’s effects. Studies were excluded from this review if they offered only correlational evidence for a possible causal effect of the law, such as showing that states with a specific law had lower firearm suicides at a single point in time than states without the law. Correlations like these can occur for many reasons other than the effects of a single law, so this kind of  evidence provides little information about the effects attributable to specific laws. We did not exclude studies on the basis of their findings, only on the basis of their methods for isolating causal effects. For studies that met our inclusion criteria, we summarize key findings and methodological weaknesses, when present, and provide our consensus judgment on the overall strength of the available scientific evidence."
One main result is that the actual evidence is pretty thin. "Of more than 100 combinations of policies and outcomes, we found that surprisingly few were the subject of methodologically rigorous investigation." For example, evidence on four of the eight outcomes was "essentially unavailable," including defensive gun use, officer-involved shootings, hunting and recreation, and effects on the gun industry. None of the studies of waiting periods and licencing and permitting requirements have reached more than inconclusive results. There are no methodologically sound studies at all on the effects of gun-free zones or requirements for reporting of lost or stolen firearms. I'll just list the study's overall conclusions here:
Conclusion 1. Available evidence supports the conclusion that child-access prevention laws, or safe storage laws, reduce self-inflicted fatal or nonfatal firearm injuries among youth. There is moderate evidence that these laws reduce firearm suicides among youth and limited evidence that the laws reduce total (i.e., firearm and nonfirearm) suicides among youth.
Conclusion 2. Available evidence supports the conclusion that child-access prevention laws, or safe storage laws, reduce unintentional firearm injuries or unintentional firearm deaths among children. In addition, there is limited evidence that these laws may reduce unintentional firearm injuries among adults. ...
Conclusion 3. There is moderate evidence that background checks reduce firearm suicides and firearm homicides, as well as limited evidence that these policies can reduce overall suicide and violent crime rates.
Conclusion 4. There is moderate evidence that stand-your-ground laws may increase state homicide rates and limited evidence that the laws increase firearm homicides in particular.

Conclusion 5. There is moderate evidence that laws prohibiting the purchase or possession of guns by individuals with some forms of mental illness reduce violent crime, and there is limited evidence that such laws reduce homicides in particular. There is also limited evidence these laws may reduce total suicides and firearm suicides. ...

Conclusion 6. There is limited evidence that before implementation of a ban on the sale of assault weapons and high-capacity magazines, there is an increase in the sales and prices of the products that the ban will prohibit.

Conclusion 7. There is limited evidence that a minimum age of 21 for purchasing firearms may reduce firearm suicides among youth.

Conclusion 8. No studies meeting our inclusion criteria have examined required reporting of lost or stolen firearms, required reporting and recording of firearm sales, or gun-free zones. ...

Conclusion 9. The modest growth in knowledge about the effects of gun policy over the past dozen years reflects, in part, the reluctance of the U.S. government to sponsor work in this area at levels comparable to its investment in other areas of public safety and health, such as transportation safety. ...

Conclusion 10. Research examining the effects of gun policies on officer-involved shootings, defensive gun use, hunting and recreation, and the gun industry is virtually nonexistent.

Conclusion 11. The lack of data on gun ownership and availability and on guns in legal and illegal markets severely limits the quality of existing research. ...

Conclusion 12. Crime and victimization monitoring systems are incomplete and not yet fulfilling their promise of supporting high-quality gun policy research in the areas we investigated. ...

Conclusion 13. The methodological quality of research on firearms can be significantly improved.
Of course, absence of evidence is not evidence of absence--that is, just because there is a lack of evidence on certain policies or outcomes doesn't prove that those policies don't work. But it does suggest that a degree of humility might be appropriate on all sides. As a hopelessly out-of-touch academic, perhaps there could be bipartisan consensus on building up the data and evidence so that better studies can be done, but maybe this is a situation where neither side wishes to take the risk tha their presuppositions might be rebutted. Or at least when gun control laws are passed, the law could include a specific provision for exactly how those laws will be meaningfully evaluated a few years down the road.

Follow-up on 3/13/18: Faithful reader DK reminds me that Congress blocked the public health authorities from doing research into gun control issues back in the 1990s, as the New York Times just reported.  I'm pretty much always in favor of additional research, and I don't like research being limited  That said, it seems pretty clear to me as someone who has never fired a gun and tends to favor additional gun controls that most public health researchers then and now have been so  stridently anti-gun that their research was not trustworthy. I also tend to view gun policy as a social science issue, which is best tackled with the social science research methods like those considered in the RAND report. It's not clear to me that public  health researchers have the tools or expertise to address it appropriately.