According to Wikipedia the numbers reported range from 65 thousand to 2.5 million. I am very skeptical of the 2.5 million figure and in fact I am even skeptical of the 65 thousand figure. This Wikipedia page lists documented cases where guns were used defensively and only 34 incidents are listed for 11 months of 2012. I assume the people that are against any gun control would make sure any gun use that had real documented evidence would be included on that page, so I really doubt there are even 65 thousand incidents. At 65 thousand incidents per year, there would be 180 incidents per day, why would only there only be an average of 1 documented incident per 10 days?

Are there any other more authoritative studies that don't rely on survey evidence? What is the truth?

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    Wikipedia provides academic references to support those figures. It also better explains the different definitions that account for the apparent discrepancy. Are you skeptical of those source? If so, why? I am trying to avoid just regurgutating the exact same links as Wikipedia has already provided. – Oddthinking Dec 18 '12 at 0:24
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    Yes, I am very skeptical of the 2.5 million figure and in fact even the 65 thousand figure. The en.wikipedia.org/wiki/… page only lists 34 incidents in 2012 that were documented per the criteria of that article and I assume the people that are against any gun control would make sure any use that had real evidence would be included there. Are there any other more authoritative studies that don't rely on hearsay evidence? – FrankH Dec 18 '12 at 1:04
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    I can't answer, because I haven't read the study, but I imagine the claim "2.45 million crimes were thwarted each year in the United States, and in most cases, the potential victim never fired a shot in these cases where firearms are used constructively for self-protection" might include crimes that were never committed because the potential criminal was aware that the victims, the witnesses, security guards and the police might have firearms. – Oddthinking Dec 18 '12 at 1:28
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    I agree with @Oddthinking's comment. Cases were firearm was successful deterrent are not reported at all. Moreover, I can imagine the case, where potential victim would not be aware. Theoretical situation someone plans to hit convenient store, but upon realizing that owner is armed never does anything. That wouldn't be ever reported. Of course it's double edged, you can imagine that the perpetrator wouldn't even be planning to hit convenient store if he hadn't had firearm (although correct me if I'm wrong, but in UK assaults at knifepoint aren't unusual). – vartec Dec 18 '12 at 13:06
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    many incidents would go unreported simply because police have a terrible record of interacting with legally armed citizens. – Ryathal Dec 18 '12 at 13:46

I asked the question and have at least a partial answer after reading some of the published research.

First of all, the 65,000 number of defensive gun uses per year is based on data from the National Crime Victimization Survey (NCVS) and I was unable to download the actual study - my computer complained the PDF file was corrupted. So I cannot explain the factor of 2000 discrepancy between the 65,000 number and the documented 34 incidents in 11 months of 2012.

However, there is reason to be skeptical of the far higher reported rates of defensive gun use based on telephone surveys. In particular, there are two studies reporting roughly 2 million defensive gun uses per year: the Kleck and Gertz study that reported the 2.5 million use estimate and the Department of Justice study that reported a 1.5 million use estimate. Both of these studies were based on national random telephone surveys of about 4500 and 2500 households respectively. The reasons to be skeptical about these survey results are stated by the authors of the Department of Justice survey as shown in all the quotes below:

First, of all, using a survey to estimate the rate of occurrence of a rare event will suffer from the false positive effect. The study authors state (where DGU = defensive gun use and my emphasis is added in bold):

Any estimate of the incidence of a rare event based on screening the general population is likely to have a positive bias. The reason can best be explained by use of an epidemiological framework.[15] Screening tests are always subject to error, whether the "test" is a medical examination for cancer or an interview question for DGUs. The errors are either "false negatives" or "false positives." If the latter tend to outnumber the former, the population prevalence will be exaggerated.

The reason this sort of bias can be expected in the case of rare events boils down to a matter of arithmetic. Suppose the true prevalence is 1 in 1,000. Then out of every 1,000 respondents, only 1 can possibly supply a "false negative," whereas any of the 999 may provide a "false positive." If even 2 of the 999 provide a false positive, the result will be a positive bias--regardless of whether the one true positive tells the truth.

Respondents might falsely provide a positive response to the DGU question for any of a number of reasons:

o They may want to impress the interviewer by their heroism and hence exaggerate a trivial event.

o They may be genuinely confused due to substance abuse, mental illness, or simply less-than-accurate memories.

o They may actually have used a gun defensively within the last couple of years but falsely report it as occurring in the previous year--a phenomenon known as "telescoping."

Of course, it is easy to imagine the reasons why that rare respondent who actually did use a gun defensively within the time frame may have decided not to report it to the interviewer. But again, the arithmetic dictates that the false positives will likely predominate.

The study authors then go on to state (here NSPOF = National Survey of Private Ownership of Firearms - this survey):

In line with the theory that many DGU reports are exaggerated or falsified, we note that in some of these reports, the respondents' answers to the followup items are not consistent with respondents' reported DGUs. For example, of the 19 NSPOF respondents meeting the more restrictive Kleck and Gertz DGU criteria (exhibit 7), 6 indicated that the circumstance of the DGU was rape, robbery, or attack--but then responded "no" to a subsequent question: "Did the perpetrator threaten, attack, or injure you?"

So note that these reported statistics rely on only 19 respondents to generate the 1.5 million estimated rate of defensive gun uses and that some of these 19 reports were inconsistent. Another possible unreliable report was:

one woman reported 52 (defensive gun uses in a year)!

The survey authors also state:

Some troubling comparisons. If the DGU numbers are in the right ballpark, millions of attempted assaults, thefts, and break-ins were foiled by armed citizens during the 12-month period. According to these results, guns are used far more often to defend against crime than to perpetrate crime. (Firearms were used by perpetrators in 1.07 million incidents of violent crime in 1994, according to NCVS data.)

Thus, it is of considerable interest and importance to check the reasonableness of the NSPOF estimates before embracing them. Because respondents were asked to describe only their most recent defensive gun use, our comparisons are conservative, as they assume only one defensive gun use per defender. The results still suggest that DGU estimates are far too high.

For example, in only a small fraction of rape and robbery attempts do victims use guns in self-defense. It does not make sense, then, that the NSPOF estimate of the number of rapes in which a woman defended herself with a gun was more than the total number of rapes estimated from NCVS (exhibit 8). For other crimes listed in exhibit 8, the results are almost as absurd: the NSPOF estimate of DGU robberies is 36 percent of all NCVS-estimated robberies, while the NSPOF estimate of DGU assaults is 19 percent of all aggravated assaults. If those percentages were close to accurate, crime would be a risky business indeed!

In addition the authors note:

Should the number of DGUs serve as a measure of the public benefit of private gun possession, even in principle? When it comes to DGUs, is more better? That is doubtful, for two kinds of reasons:

o First, people who draw their guns to defend themselves against perceived threats are not necessarily innocent victims; they may have started fights themselves or they may simply be mistaken about whether the other persons really intended to harm them. Survey interviewers must take the respondent's word for what happened and why; a competent police investigation of the same incident would interview all parties before reaching a conclusion

o Second and more generally, the number of DGUs tells us little about the most important effects on crime of widespread gun ownership. When a high percentage of homes, vehicles, and even purses contain guns, that presumably has an important effect on the behavior of predatory criminals. Some may be deterred or diverted to other types of crime. Others may change tactics, acquiring a gun themselves or in some other way seeking to preempt gun use by the intended victim.[16] Such consequences presumably have an important effect on criminal victimization rates but are in no way reflected in the DGU count

So, my conclusion is that these kinds of random telephone surveys are not an accurate way to estimate the annual rate of defensive gun use in the US.

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    the number of rapes prevented by a gun could be greater than the number of rapes. lets say women is pulled into alley and while potential rapist is trying to remove her clothes, she shoots and kills potential rapist. Does that count as both a rape and a defense of rape with a gun, or just a defense of rape since the rape part never actually happened? This occurring with enough frequency to actually outnumber total rapes does seem incredibly implausible. – Ryathal Dec 18 '12 at 19:44
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    @Ryathal Thing is, I imagine that actual defensive gun use is going to leave a paper trail - if someone dragged you into an alleyway, you pulled a gun on them and then they ran off, are you just going to merrily go on your way? Hell no, you'll call the police to report it. That goes double if you actually shoot or kill your assailant - the police will definitely want to know about that. All the paperwork this generates is excellent research fodder, and the fact that it seems almost non-existent is quite odd. – Tacroy Dec 18 '12 at 23:41
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    @Tacroy : (1) I'm not sure that the kind of people who carry around weapons for self defence would go and call the police when someone attempted to rob them but she just pulled their gun and the person ran away. They kind of people who carry guns for self defense are on average probably less trusting in the police than other people. (2) Defensive gun use isn't a crime. Police therefore won't aggregate those uses in the same way they aggregate other crime data. – Christian Dec 19 '12 at 12:51
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    @KonradRudolph - frankly, the number is rather irrelevant, in large part due to reason #1 in preceding comment. Given the average attitude by police to people with concealed gun permits, a vast majority would have a great incentive to avoid the hassle/risk of filing a report in a large amount of US locales. IOW, barring a well designed anonymous survey, any official reports will be inacurate as hell. – user5341 Dec 21 '12 at 3:18
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    @DVK I’d have to agree with that. On the other hand, I simply don’t believe that number at all, it’s way too high – consider, for instance, that every competent instructor will tell you that if you get mugged, just give the guys your money, do not go for your gun – it’s way too dangerous. I don’t think there are very many situations where a concealed weapon actually confers security (of course there are some; a shop owner being mugged at knife’s point, a person in a potentially lethal situation, as a bystander when somebody gets harassed etc.). – Konrad Rudolph Dec 21 '12 at 10:33

"A CALL FOR A TRUCE IN THE DGU WAR", by Tom W. Smith, (published in Journal of Criminal Law and Criminology (Northwestern) 87 (1997): 1462) discusses this. (DGU stands for Defensive Gun Use.)

TL;DR: the truth is somewhere between both of the extremes (the low 55k-80k of NCVSs and the high of 2.5M of Kleck-Gert). But "more studies are needed".

If we factor in some of the probable over- and underestimates affecting the NCVS and K-G 1993 survey, the widely divergent figures on DGUs draw much closer together. The latest figures from the NCVS indicate 108,000 DGUs per annum. [40] If this is adjusted for a 50% under-reporting due to not directly asking for DGUs, this increases the estimate to 216,000. Next, research by Cook and Ludwig suggests that perhaps 16-42% of DGUs involve crimes not covered by the NCVS. [41] Adding in these would raise DGUs to 256,500-373,000.

Similarly, using the average of the K-G one-year lower (B) estimate and the NSPOF figure gives a starting estimate of 1,810,000. Assuming a net cognitive over-reporting (telescoping-forgetting) of 50%, [42] reduces the figure to 1,210,000. [43] These estimates should draw even closer together if other measurement errors could be factored in. [44] But even as they stand, the gulf has been narrowed from 30+:1 to 3.2-5.6:1.

Of course, the above calculations are based on reasonable, but mostly unconfirmed, estimates of various error parameters. What is needed is less argumentation and speculation and more and better data. First, some additional information can be gained by refined analysis of the existing surveys (K-G 1993, NSPOF, NCVS, etc.). Each [Page 1469] of the surveys should be fully documented and archived at the Roper Center, University of Connecticut, and the Interuniversity Consortium for Political and Social Research, University of Michigan, for any researcher to use. [45]

Second, more studies are needed. These should include: (1) validation studies specifically designed to ascertain whether a social desirability bias exists for DGUs; (2) studies that experimentally vary factors that are believed to inflate or deflate DGUs reports to see (a) how robust reports are and (b) whether they are affected by the hypothesized factors; (3) taped descriptions of reported DGUs with detailed probes so that one can determine exactly what transpired, including such issues as whether (a) a criminal threat existed, its nature, and seriousness, (b) the DGU was probably legal, and (c) accounts are accurate and truthful; (4) trying alternative methods for measuring DGUs that might lessen both any self-presentation bias and cognitive error. One possibility would be to ask people whether they had handled or fired a gun in the last year and then ask about for what purpose it was used (e.g., hunting, target shooting, self-defense, etc.); and (5) the use of refined, direct experience questions on a large, high quality, panel survey with explicit corrections for telescoping. Adding a few questions to the NCVS would be the easiest way to achieve this. Only by such further careful, empirical research will the errors in measuring DGUs be understood and the true level of DGUs ascertained.

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protected by Oddthinking Feb 28 '13 at 22:37

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