Recently a number of ScienceBloggers including Mark Hoofnagle of Denialism and myself have written posts about guns and gun control in the United States. While the internet tends to generate more heat than light, we decided that it might be worth having a discussion and debate about the subject. His opening salvo is here, at his blog. I recommend reading it first. He argues that substantial new gun control is both necessary and helpful, and I will generally disagree. As always, I apologize to my physics readers for yielding to the temptation to wax political. I know I dislike it when my favorite non-political writers jump on their soapboxes. So for those of you who're not interested in this sort of thing, please skip this and be assured that there's plenty of physics posts in the pipeline as well.

By the rude bridge that arched the flood,

Their flag to April’s breeze unfurled,

Here once the embattled farmers stood,

And fired the shot heard round the world.

- Ralph Waldo Emerson, "Concord Hymn"

American independence began with a shot fired from an anonymous man's personal musket. In the centuries since, the gun has become embedded into the American mythos from the rifles of the pioneers to the revolvers of the cowboys. This culture has not diminished in the present day. There are roughly as many firearms in the US as people, and though self-reported data is notoriously unreliable, somewhere between one third and one half of households own at least one firearm. The reasons for this choice are as diverse as the country itself. For some, it's a marker of self-reliance, a sign that in this country power flows from the people in a way that's not merely symbolic. For others, it's shouldering the responsibility for the defense of self and family in a way that doesn't rely on the vagaries of police patrol density and response time. Still others see it as a vital backstop against the the breakdown of civil order in the event of natural or man-made disaster. More still use their firearms to put food on the table in a natural way that doesn't rely on grim stainless steel factory farms. Any of these are good reasons for a responsible person to consider firearms ownership, and their choice to do so puts them in a long and unique tradition of keeping and bearing arms.

Yet this culture of firearms ownership has its opponents. In the US in 2011, some 8,583 people were murdered by assailants using firearms. In 2012, mass murders at a theater and an elementary school shocked the nation in a way that hasn't been felt in many years. Both were committed with firearms. In the wake of these attacks, debate over guns in the United States has reignited. Mark has penned his own contribution, in which he argues along four lines. First, that gun control will reduce acts of mass violence. Second, that gun control will reduce violent crime generally. Third, that specific gun control methods he enumerates ought to be put in place in view of the previous two points. Fourth, that a number of ancillary pro-gun arguments are spurious and ought not have a place in serious discourse. I will respond to each of them in turn.

In its coverage of the recent attacks, the strongly anti-gun publication Mother Jones has compiled a list of mass shootings since 1980. Though my disagreement with their editorial conclusions can hardly be overstated, I both admire their resolve to stick to a data-driven analysis and am glad to have a data source which can't easily be accused of bias in my favor. The first key point is the extreme rarity of mass violence. In the 32 years since 1980, there have been some 513 people killed in 62 incidents of mass shootings under the Mother Jones definition (perpetrators generally included). This amounts to an average of 16 per year. Over the 12 years for which the CDC has available data, the average death rate due to lightning strikes has been 45 per year. All other things being equal, you are almost three times more likely to be killed by lightning than you are to be killed by a mass shooter. Now any preventable cause of even a single death should be prevented, and while mass murder shocks the conscience in a way that the anonymous and impersonal forces of nature cannot, this ought to cause us to pause and consider whether what is being proposed will actually do any good. The choices we make in response to these tragedies will have consequences that we foresee and consequences we don't. These consequences may well include the failure of new laws to save anyone in the future. This concern is not hypothetical - we're well over a decade into our government's frantic response to 9/11, and we may well be less safe than we were on 9/10.

We could begin by looking at whether or not semi-automatic rifles are actually a particularly heinous implement of death (we will discuss handguns in the "crime generally" section). In 2011, the United States experienced a total of 2,437,163 deaths. Of these, 12,664 were victims of murder. So for every 192 people who died in the United States, one was a victim of murder. Of those 12,664 murder victims, 323 were killed by a rifle. Thus for every 40 people who were victims of murder, one was shot by a rifle. This comes in well behind knives or blunt objects or even bare hands. In terms of death toll, rifles are roughly on par with falling off ladders (which killed 404 in the year 2010). And this category comprises all rifles, from bolt-action deer rifles to AR-15s to .50-caliber Barretts.

One might be tempted to speculate that while the absolute numbers of rifle fatalities are small, their combat effectiveness makes them disproportionately dangerous in the context of random acts of mass violence. Mark, for instance, notes that a recent knife attack in China wounded many children but killed none. This conclusion, though tempting, is numerically dubious. A number of other Chinese knife/hammer attacks at schools since 2010 have indeed between them exceeded the Connecticut death toll, but far and away the most effective weapons of mass murder are bombs and, for the less technically capable psychopaths, the kitchen match. The Bath School bombing in 1927 killed more than Sandy Hill and Columbine combined. Julio González killed 87 in the Bronx in 1990 with a match and some gasoline. The most lethal female mass killer in America used a Lincoln Continental. The unknown perpetrators of the Black Saturday fires in Australia killed many times more people than the Port Arthur massacre that touched off that nation's much stricter gun laws. Now a list of anecdotes is not dispositive, but it is surprisingly hard to find comprehensive academic lists of rampage killings for the purpose of comparing across borders and between gun and non-gun attacks. At any rate the Wikipedia compendium of rampage killings internationally is striking (if not rigorous) reading - it lists 119 mass killings in the Americas and 100 in Europe.

Though non-gun massacres have been extremely lethal, one might speculate that at least gun control could prevent those that are gun-related. This has not seemed to be the case as regards firearms-related mass murder in other countries. The United Kingdom, a country with 1/5 of the US population, has experienced several mass shootings despite very strict gun control. The Dunblane school massacre in 1996 killed 17 in an environment more restrictive than even what Mark advocates. The further tightening of those laws - to the point of completely banning civilian possession of handguns - failed to prevent the Cumbria shootings in 2010. The same holds elsewhere in Europe. Of course the Norway shooting is well-known, but many others are less so. As I mentioned earlier I am unaware of a comprehensive list of European mass murders generally, which would allow us to make per-capita comparison. I would like to see one, should any of you know where to find a rigorous systematic study. The best example on the pro-gun-control side is that of Australia, in which guns are regulated under a regime which has been a near ban since the Port Arthur massacre in 1996. There has nonetheless been at least one school shooting since then, though fortunately it only resulted in two deaths. A mass shooting of 4 or more victims has not occurred since 1996. The total rate of mass killings by arbitrary methods did not change significantly, and overall homicide rates were unaffected[1]. It is a matter of conjecture as to what extent this quite modest success in a island nation of a very different culture and just 10% of the US population can be extrapolated to the US. (Here's a data point for the difference in firearms culture: the Australian buyback program after Port Arthur brought in 631,000 firearms. US citizens bought almost three million last month alone.) In summary, mass violence, despite its considerable press, is exceptionally rare, not particularly reliant on guns, and not particularly preventable by gun control.

Now it's worth taking a look at violent crime generally. While an uncommon cause of death in percentage terms, murder is a significant source of mortality in the United States. Of murders in the United States in 2011, 8,583 (about two thirds) were committed with firearms. Of firearms murders, the overwhelming majority were committed with handguns (6,220 with certainty, and likely most of the 1,587 "type not specified"). The rate of homicides (by all methods) is about 4.8 per 100,000, which is high compared to Australia (1.0) the UK (1.2), or Canada (1.6). On the other hand, it's low when compared to most nations outside the highly developed first world, such as Russia (10.2) and Mexico (22.7). The highest, Honduras, is a staggering 91.6.

Which comparisons are fair, and what are the causal factors? Here's a cautionary tale - one very similar nation has a homicide rate of 9.8, more than twice that of the US. That nation was the US, in 1991. What changed? Sociologists differ, but it was certainly not due to stricter gun laws. (One frequently-mentioned and surprisingly robust possibility is reduced childhood lead exposure after lead was phased out of gasoline.) Simultaneous declines took place in many other developed nations to various extents. If non-gun factors can change the murder rate within the same country by more than a factor of two, it is extremely challenging to say anything about the effects of gun laws in nations with very different cultures, histories, economies, and demographics. And we shouldn't kid ourselves, the culture, history, economy, and demographics of the US are very different than most of the rest of the small class of highly-developed western nations. For that matter, the nations of that class with lower murder rates than ours have always have had lower murder rates, even in the eras when their gun laws (and our own) were quite different. The homicide rate in England has not been substantially north of 1 per 100,000 since the year 1800. Mark dismisses any comparison to Mexico, but the comparison is more instructive than it first appears. The population of the Texas border city of El Paso is some 75% Mexican (and more than 80% Hispanic), but its homicide rate is a relatively bucolic 0.8 per 100,000. Its adjoining Mexican neighbor of Juarez is one of the most violent places on the planet, peaking at a hideous 130 per 100,000 in 2009. Do El Paso's gun-friendly Texas laws make it so much more peaceful than Juarez? I doubt it. But it does put to bed the idea that gun laws are the primary or even a significant driver of the crime rates.

Within the US, violence in general and gun violence specifically are not evenly distributed. To enormous racial gap is well-known - the number of white murder victims[2] divided by the census number of white Americans gives a rate of 2.6 per 100,000. (This would be at the high end of western European homicide rates. Finland at 2.2 is the highest in western Europe. Outside of western Europe the rate is higher. The Baltics contain typical examples: Latvia is around 3, Lithuania and Estonia are around 5 to 6.) The equivalent rate for black Americans is 16.3 per 100,000. Gun laws are of course the same for both groups within a given state. As demonstrated by the El Paso vs. Juarez comparison, skin color means nothing by itself, but as a proxy for deeper cultural and socioeconomic factors it shows how little difference gun laws make. Since most murder victims have criminal records, one more possibly more parsimonious explanation for some of the murder rate in Mexico and many American urban cores is violence directly or indirectly related to the saturation of organized crime including the drug trade. Please note that I am not blaming the victim - the perpetrator is the person with sole moral responsibility. But to the extent that statistical patterns in the victims exist, we should examine them to see how they might be broken. The complete disconnect between gun laws and violent crime indicates that this is an ineffective way to try to break the pattern. It will be interesting to see if the recently-relaxed marijuana laws in some states result in reduced violence associated with the fact that criminal organizations no longer have exclusive control over its sale. While I am already generally opposed to the drug war as currently constituted, its end or at least reform could potentially be an effective anti-violence measure.

At this point we move on to Mark's specific suggestions as to new gun control laws. The first is "significant restrictions on civilian ownership of magazine-fed semi-automatic weapons". Here we hit the first problem. This category amounts to all firearms which fire one shot per trigger pull, which is itself very close to "all firearms". The only modern firearms which are not semi-automatic and are sold in any meaningful quantity are bolt-action rifles, pump-action shotguns, and revolvers. Revolvers are functionally semi-automatic in that they fire one shot per trigger pull though they aren't classified as semi-automatics for technical reasons[3]. If you include them, you've come close to banning civilian handgun ownership. This is politically impossible, legally dubious, and not likely to put a dent in mass shootings, much less mass killings generally.

Well, you could try restrictions that don't amount to a ban. Mark suggests requiring a "legitimate reason" for ownership. While I would certainly object to self-defense not being a reason (and that reason applies to everyone), we already have good evidence that this type of "good reason" scheme is futile. California has a "may-issue" concealed carry system, where the issue of permits is at the discretion of the local county's evaluation of your stated reason. As a result, some counties issue to effectively everyone, and some counties issue to no one, or only to the famous or politically well-connected. Or rich, as has been pointed out in New York. Just the paperwork to possess a handgun in NYC costs north of $400. A huge fee merely to ask for some bureaucrat's personal fiat is the antithesis of equal protection under the law, and unworkable in a society that respects the rule of law. It's evadable too - Anders Breivik jumped through Norway's considerable hoops without trouble. Conversely, I'm with Mark in favor of safe gun storage, and in fact most new guns in the US are automatically sold with locks. Many states already have criminal penalties for not adequately securing guns against children. Criminal penalties for having your guns misused more generally are not reasonable. Locks and safes are breakable, often with something as simple as a sledgehammer (of course locks and safes are still a good idea, but far from infallible), and it is unacceptable to put people in jail for being the victim of a crime. Limits on magazine capacity are also unlikely to accomplish anything positive. I have seen no evidence that ordinary crime either requires or typically involves more than one or two shots. Mass shootings by definition involve more, but the numbers involved indicate that the success of magazine prohibition is dubious. Of the 62 shootings listed by Mother Jones, I count only two (the Giffords shooting and the Thurston High School shooting) which were stopped when the gunman was tackled during reloading. One occurred during a ban on >10-round magazines, one didn't. The one that did actually involved more people being hit.

Mark's second main thrust is toward better policing of guns moving from legal owners to prohibited ones. Currently buying a gun from a dealer means undergoing a background check through the federal NICS system. Private sale within the same state is not prohibited federally, so in principle a prohibited person could procure a firearm by buying one from a private individual who is unaware of the buyer's criminal history. Alternately and more commonly, a prohibited person could entice a friend, romantic partner, or relative with a clean record to purchase a gun on the criminal's behalf. It is illegal to serve as a proxy buyer (a "straw purchase") even for a person with a clean record, but it does happen and seems to be the most common source of guns for criminals. Can this be prevented or mitigated? Probably so. It is possible to trace serial numbers to the original dealer, and from there to the original buyer via the Form 4473 records kept at the dealer's location. For that matter there are thousands of criminal attempts at gun stores to purchase firearms which are stopped by NICS every year, but only a few dozen convictions. This dismal rate could be improved immensely under current law. While I have serious privacy concerns with opening or requiring NICS for private sales, it is conceivable that it could be done and might have some good effect.

Finally, Mark enumerates eight pro-gun arguments which he believes are not worthy of serious attention. I'll briefly comment on each, sometimes to agree, sometimes to disagree, sometimes to clarify. (The arguments themselves are Mark's words. His own responses to them are at his post.)

1. The only thing that stops gun violence is "good guys" with guns - the argument we should arm teachers, arm principles, or place armed guards to prevent mass shootings in school. Or the even more obnoxious "when seconds count" argument.

In vast majority of cases, mass shootings are stopped when the perpetrator is shot, either by suicide or police. But we have almost no data on the possibility of concealed carry permit holders stopping mass shootings. This is not surprising. Mass shootings are extremely rare, concealed carry is rare in percentage terms (around 2% have a permit in Texas), and mass shootings almost exclusively occur in places where concealed carry is prohibited by statute or the property owner. On the other hand, in terms of raw numbers millions of permit holders rack up billions of man-hours carrying every year. Permit holders outnumber police 7 to 1 in Texas, for instance. It is unreasonable to expect that extension of concealed carry to schools will result in catastrophic movie shootouts when it has not done so anywhere else - including many college campuses. I would not suggest concealed carry in schools as a panacea in view of its lack of a track record and the small percentage who would actually do it, but I would also not suggest we automatically discount it.

2. You can kill someone with a frozen banana, hence assault weapons shouldn't be banned.

If assault weapons were actually a problem, and if banning them would actually accomplish anything, then maybe. But as it is, choking on food kills around three times as many people as assault weapons.

3. The 2nd amendment protects us from tyranny.

I understand where you're coming from. The American revolution can't be exactly duplicated in the modern world. But I don't dismiss this for two reasons. First, the long view. In living memory most of Europe fell to two different varieties of hideous tyranny, of a kind that no one could have seen coming even a few decades earlier. Fascism and communism are not descending in the US, but we would be foolish to think it's always and forever impossible. And if it did, we shouldn't assume that rifles are hopeless against stealth bombers and tanks. Unfortunately the pre-medieval primitives in the Taliban didn't make that assumption either, and they've more or less succeeded in forcing a US withdrawal. Second, and more mundanely, the 2nd amendment actually talks about the security of the state, not just overthrowing it. There are times and places where the state can suddenly fail, and at that point the people are on their own until normality can be restored. I was less than 80 miles from landfall when Katrina temporarily eliminated the entire governmental apparatus in New Orleans, and saw the need for this firsthand.

4. It's crazy people that's the problem, we need to track them, institutionalize them etc.

Many - but not all - mass shooters are nuts. But the gargantuan, overwhelming majority of the mentally ill are completely harmless. If we did have a way to better separate out the tiny fraction of the dangerous mentally ill, we would be better off. Now it's true that "better mental health treatment" is much easier said than done, though better health care is always worth working toward. There are already some easy ways we could do better, as the NICS failure to disqualify an already legally-adjudicated-ineligible Seung-Hui Cho demonstrates. Beyond that, we should tread carefully.

5. They already had an assault weapons ban, it didn't work.

As you say, it was a pointless exercise that banned cosmetic features. But as I hope to have demonstrated above, even a much more comprehensive ban is not likely to accomplish anything.

6. It's unconstitutional!

Well, there's the Constitution as the Platonic ideal of its text (or original public meaning, if you prefer), and there's the Constitution as actually interpreted by the supreme court. The proposed Feinstein ban is unconstitutional in the first sense in my opinion, but probably wouldn't be in the opinion of the nine people whose votes matter.

7. But Israel lets everyone carry guns and they don't have school shootings.

Israel is indeed a very different country. As I have argued, extrapolating from other nations in this context doesn't generally work. I agree that it doesn't work here either, in either direction.

8. It's because we don't have school prayer, the students should have rushed the gunman, it's because God isn't in schools, it's video games, it's feminists, it's doctors, it's anti-depressants etc.

Yes, these are all dumb arguments.

To conclude: gun control is very unlikely to accomplish anything positive even in the most rationally-designed best-case scenario, and the proposals being floated in DC are not even in the same zip code as rational.

[1] Of course I prefer to cite linkable material, but unfortunately academic publications are generally behind paywalls. My statement about homicides is fairly well-documented and not especially controversial in the literature. Wikipedia's article about gun politics in Australia links many typical studies by various groups on this issue of homicides in Australia. My statement about mass killings generally is taken from Evaluating Gun Policy: Effects on Crime and Violence, P 121-156, 2003, Philip J. Cook and Jens Ludwig, eds.

[2] I use victims rather than perpetrators because in a large percentage of homicides the race of the perpetrator is unknown. The great majority of homicide is intra-racial rather than inter-racial, so it's not a bad first approximation. But it's not a perfect approximation. The two major problems are the aforementioned failure to account for inter-racial homicide, and that the US is vastly more complicated than the simplistic FBI categories of "white", "black", and "other".

[3] From a technical standpoint, semi-automatic means that a single trigger pull fires a round, removes the spent cartridge from the chamber, and inserts a new cartridge into the chamber. This is almost the same thing as saying "one shot per trigger pull until you run out of ammo". The principle exception is revolvers, which are still one shot per pull, but each cartridge has its own separate chamber and the spent cartridge remains with the chamber after firing. While we're being technical, there is also a difference between a clip and a magazine. A magazine is a device that holds and feeds cartridges into a chamber. A clip is a device that feeds cartridges into a magazine. But like "invite" as a noun, nobody worries about it too much.