Dear Editor

We were dismayed to read the recent article by Denton and Fabricius in which they gleaned the magnitude of annual defensive gun use (DGU) from local newspaper accounts.[1] We find the authors’ method of determining DGUs, and their suggestion for a new way to use firearms for self-defense, seriously flawed.

The authors used the Tribune (Tempe, AZ) as a "daily survey of several million people for cases of DGU." They acknowledge that newspapers may not always report DGU incidents, but their explanation of why this under-reporting does not affect their conclusion uses only statistics for homicide data. We doubt that the same result would hold if statistics for woundings and firings were also used. Woundings and firings are not as newsworthy as homicides.

Although the authors discuss police and court records, and estimate how many incidents the police should have known about, they never reveal the actual police data.

Denton and Fabricius correctly acknowledge that merely brandishing a gun is the most common type of DGU, and suggest, therefore, that an unloaded firearm would serve the same purpose as a loaded one. This is an astounding conclusion.

A firearm represents a credible deterrent only to the extent that it is able to fire a projectile. It is this capability that causes felons to fear being shot by an armed victim.[2] Were it common knowledge among criminals that most ordinary citizens now use unloaded handguns—that some would-be victims are armed but many only pretend to be—deterrence would quickly evaporate.

Proficient professional poker players may be able to bluff effectively in such a situation, but many ordinary citizens would not. Few people would bet their lives, or those of their families, in what might amount to a suicidal bluff.

Would police officers volunteer to carry unloaded weapons?

References

1. Denton JF, Fabricius WF. Reality check: using newspapers, police reports, and court records to assess defensive gun use. Inj Prev 2004; 10:96-98.

2. Wright JD, Rossi PH, Daly K. Under the gun: weapons, crime, and violence in America. Hawthorne, New York: Aldine de Gruyter, 1983, chapter 7, 138-139.

A survey of jail inmates done by J P May, D Hemenway, and A Hall indicated that, among those who admitted to having been shot, 91% reported having gone to the hospital for treatment. This comment explains why this finding cannot be taken seriously.

Put yourself in the position of a jail inmate who was part of this survey. Most jail inmates are awaiting trial. They are the most legally vulnerable of all criminals - unlike uncaught criminals they are subject to legal punishment, yet unlike prison inmates, the punishment they will receive is still to be determined - the hammer has not yet come down. This is a set of criminals who are understandably obsessed with not looking any more criminal to the authorities than they already appear. How is this relevant to the jail survey conducted by May et al.? Suppose you were a jail inmate who had been shot, but did not seek medical treatment because you were shot while committing a crime, and knew that if did go to the hospital, police would interrogate you as to how you got shot and possibly connect you to the crime.

When such a jail inmate was asked whether they had ever been shot, either of 2 things would happen. The inmate would either accurately answer "yes" or would falsely deny having been shot, for the same reason that they did not seek hospital treatment - they did not want to be connected to the crime they were committing when they were shot. These inmates would not be asked the follow-up question "Did you go to the hospital for treatment of that wound?" They would simply be excluded from further analysis, and therefore would not go into the computation of the percent of the 307 gunshot-wounded inmates who had sought hospital care. Instead, they would erroneously be placed in the set of 1,816 inmates who did not report being shot. This is what is known to researchers as a "censored sample" - the inmates who had been shot while committing a crime and who did not seek hospital treatment would largely be "censored out" of the sample, leaving mostly inmates who been shot in less incriminating circumstances. It is scarcely surprising that many of these 307 inmates had sought medical treatment - those who were relatively "innocent victims" had no reason not to go to the hospital. This sample, however, can tell us nothing about the share of all criminals who are shot who received hospital treatment, and certainly can tell us nothing about the share of those shot by their victims while attempting a crime who received hospital treatment.

Now consider those who accurately reported having been shot, among those who had been shot by their victim while attempting to victimize them, and who consequently did not go to the hospital. These inmates may have been willing to report that they had been shot because they did not anticipate the surveyors asking any follow-up questions, such as the one concerning medical treatment. They were then asked the question as to whether they went to the hospital to get treated. At that point, an inmate of this sort could either accurately answer "no" or lie and answer "yes." How is such an inmate likely to perceive a truthful "no" answer? There is no sensible legitimate reason why an innocent victim of a gunshot wound would not seek professional medical treatment - being shot is a very serious injury, and the medically sensible step is to seek professional treatment of the injury. Only a person with something to hide from the police in connection with that wounding would avoid going to the hospital. The inmate knows this, and knows that the surveyors know it as well. So how likely is it that this inmate, in these legally vulnerable circumstances, would honestly answer "no"? Doing so would be tantamount to confessing to yet another crime that the authorities did not yet know about. Thus, there would be a powerful motivation to falsely answer "Yes," and no strong motivation to accurately answer "No," beyond the inmate's commitment to the general moral norm that one should not lie - a commitment that is likely to be lower in a sample of jail inmates than in the population as a whole.

In sum, (1) the subsample of jail inmates who had admitted having been shot is likely to have excluded most of those who had avoided hospital treatment because they were committing a crime when they were shot, and (2) among those who admitted being shot, few inmates were foolish enough to admit they had not sought medical treatment. Consequently, the claim that 90% of the inmates who had been shot had gone to the hospital cannot be given much credence.

The implicit underlying assumption of the researchers was that one could expect truthful answers from jail inmates who had powerful reasons to not be truthful. To be sure, those who had been shot as innocent victims could afford to seek hospital treatment and could be truthful about doing so when surveyed. These inmates probably account for most of the 316 inmates who reported seeking treatment. In contrast, it is extremely unrealistic to expect truthful answer from those who were shot by their victims while committing crimes that the authorities either did not know about, or did not know the inmate had committed. Inmates have no reason to conceal crimes that the authorities already know about, and prior research shows that they are indeed willing to self-report these offenses in surveys. Crimes for which the offender was never arrested are another matter entirely.

Conflict of Interest:

None declared

Dear Editor

The main conclusion of Cook and Sheikh,[1] that a bicycle helmet prevents 60% of head injuries, is incorrect due to a fundamental error in the way they have treated their percentages. A correct analysis demonstrates unequivocally that there must be major confounding factors in their data set that they have failed to take into account, and therefore any estimate of helmet effectiveness is purely speculative.

Assuming that their basic analysis of the data is correct (although the numbers they quote in the text do not actually appear to match the figure plotted), they arrive at a figure of a 3.6% for the reduction in the head injury (HI) rate for cyclists, over and above the "background" reduction that pedestrians have also seen. They assume that this drop in HI is due to increased helmet-wearing. However, this reduction is presented in terms of the number of percentage points, and relative to the baseline value of 27.9% HI for cyclists in 1995-6 it actually represents a 3.6/27.9 = 13% drop in the HI rate.

The decrease in the number of helmetless cyclists over the same interval is 5.8 percentage points from a baseline of 84% unhelmeted, giving the percentage drop as 5.8/84 = 7%. Cook and Sheikh calculate helmet effectiveness to be given by the ratio 3.6/5.8 = 60%. However the correct expression to use is 13/7 = 186%. In other words, "helmet effectiveness" is so high that each helmet does not just save its wearer, but a non-wearer too. At this rate, head injuries would be eliminated completely if just a little over half of all cyclists wore them! This is clearly ludicrous.

A more reasonable conclusion to draw from this would be that there are some other factors that are responsible for the large drop in HI rate, and therefore any attempt to attribute some part of the total 30% (8.49/27.9) change to the provably marginal impact of a very small number of extra helmet wearers is at best highly speculative and fraught with inaccuracy.

What makes this all the more poignant is the fact that the authors have recently produced a book entitled "Basic skills in statistics"!

Reference

1. A Cook and A Sheikh Trends in serious head injuries among English cyclists and pedestrians Inj Prev 2003; 9: 266-267.

Dear Editor

Nagata et al. reported effectiveness of Japanese law against alcohol-impaired driving, which would serve as a useful reference to other countries.[1] However, for this paper to be really helpful to policy makers, the description of legislation should be accurate; and changes other than the road traffic law, which might have influenced the results, should also be described.

The authors stated the fine against alcohol-impaired driving (AID) increased from 50 000 yen to 500 000 Yen.[1] This is misleading because there are two types of AID in Japan, to which different penalties are applied. Deshapriya et al. described the differences in details: in their words, driving under the influence (DUI) is determined by breath testing and driving while (heavily) impaired (DWI) is determined by the police officers' judgment on drivers' behaviors.[2] Heavier penalties are applied to DWI which is considered to be more dangerous. Before the law amendment, penalties against DUI and DWI were up to three months imprisonment or up to 50 000 Yen fine, and up to two years imprisonment or up to 100 000 Yen fine, respectively (one was imposed a fine thorough a summary procedure unless the one chose a formal lawsuit instead or was a repeated offender). These penalties were increased in June 2002 to one year or 300 000 Yen and three years or 500 000 Yen, respectively.[3] Heavier penalties against DWI have been seldom applied: in 2001 DWI penalties were applied only to 1 % of drivers charged with AID, which increased to 1.3 % in 2003.[3] Therefore, in most of the cases after the new law was implemented, fines imposed to charged drivers were up to 300 000 Yen.

The authors stated the new law made bartenders and passengers culpable.[1] Actually those who provided charged drivers with alcohol or a vehicle, and passengers had been punished as accomplices with the aid of a criminal law articles 61 and 62 that prescribe punishment against those who support a crime until September 2007 when the road traffic law was amended again. The latest law prescribes punishment against those who provided charged drivers with alcohol or a vehicle and passengers; penalties against DUI and DWI were increased to three years imprisonment or up to 500 000 Yen fine and five years imprisonment or up to 1 000 000 Yen fine, respectively.[4]

The authors discussed that no major change other than the new road traffic law occurred between 1998 and 2003.[1] Although there was no other major change in the road traffic law during this period, there was a big change in the criminal law in December 2001. Before that, penalty against those who hit a person while AID resulting in death was up to five years imprisonment. The new criminal law prescribes up to 20 years imprisonment to those who kill a person while dangerous driving including AID.[3] This implies that crashes due to AID which used to be just a mistake has become a homicide crime. This change cannot be ignored because the reduction of deaths due to AID might be at least partly because of the new criminal law. The number of drivers charged with AID started to decline before the increases of the fines (figure).

Figure 1

Another point that should be considered is a possibility of misclassification of AID as non-AID. The new road traffic law did not increase penalties against refusal of breath testing, which was 50 000 Yen fine until November 2004 when it was increased to fine same as that of DUI. Increased refusal by 52.5% was reported in June 2002 to May 2003 compared to the previous one year.[5] Furthermore, penalties against hit and run, though increased from up to three years imprisonment or up to 200 000 Yen fine to five years or 500 000 Yen in 2002, have been less severe compared to the criminal law prescribing up to 20 years imprisonment against dangerous driving resulting in death. Occurrence of hit and run started to increase concurrently with the decline of charged drivers for AID (figure). Drunk drivers involved in a crash might have chosen to be charged with refusal rather than DUI, or escaped to be charged with hit and run especially when there was a possibility of 20 years imprisonment. Therefore, we suggest that the authors analyze the trend of non-AID fatalities whether there is an upward change.

References

1. Nagata T, Setoguchi S, Hemenway D, Perry MJ. Effectiveness of a law to reduce alcohol-impaired driving in Japan. Inj Prev. 2008;14(1):19-23.
2. Deshapriya EB, Iwase N. Impact of the 1970 legal BAC 0.05 mg% limit legislation on drunk-driver-involved traffic fatalities, accidents, and DWI in Japan. Subst Use Misuse. 1998;33(14):2757-88.
3. National Police Agency. Police White Paper 2005. (in Japanese.) Tokyo: Natioal Police Agency, 2005. 20-21.
4. National Police Agency. Kaisei dorokotsuhono gaiyo. [Amendment of the road traffic law.] (in Japanese.) National Police Agency, 2007. http://www.npa.go.jp/koutsuu/kikaku190906/2_kaisei/Taro10-2.pdf (accessed on 19 Feb 2008)
5. National Police Agency. Inshu untentaisakuno jokyonitsuite. [Countermeasures against alcohol-impaired driving.] (in Japanese.) National Police Agency, 2003. http://www.npa.go.jp/comment/result/koutsuukikaku2/honbun/betu07.pdf (accessed on 19 Feb 2008)