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Table 1.  
Wounded Individuals, Circumstances, and Locations of Criminal Shootings in Boston, 2010-2014
Wounded Individuals, Circumstances, and Locations of Criminal Shootings in Boston, 2010-2014
Table 2.  
Firearm Calibers and Wounds for Criminal Shootings in Boston, 2010-2014
Firearm Calibers and Wounds for Criminal Shootings in Boston, 2010-2014
Table 3.  
Multinomial Logistic Regressions of Shooting Characteristics on Caliber
Multinomial Logistic Regressions of Shooting Characteristics on Caliber
Table 4.  
Multivariate Logistic Regressions of Caliber and Event Characteristics on Shooting Outcome
Multivariate Logistic Regressions of Caliber and Event Characteristics on Shooting Outcome
1.
Cook  PJ, Rivera-Aguirre  AE, Cerdá  M, Wintemute  G.  Constant lethality of gunshot injuries from firearm assault: United States, 2003-2012.  Am J Public Health. 2017;107(8):1324-1328. doi:10.2105/AJPH.2017.303837PubMedGoogle ScholarCrossref
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Hargarten  SW, Karlson  TA, O’Brien  M, Hancock  J, Quebbeman  E.  Characteristics of firearms involved in fatalities.  JAMA. 1996;275(1):42-45. doi:10.1001/jama.1996.03530250046025PubMedGoogle ScholarCrossref
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Fackler  ML, Malinowski  JA.  The wound profile: a visual method for quantifying gunshot wound components.  J Trauma. 1985;25(6):522-529. doi:10.1097/00005373-198506000-00009PubMedGoogle ScholarCrossref
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Webster  DW, Champion  HR, Gainer  PS, Sykes  L.  Epidemiologic changes in gunshot wounds in Washington, DC, 1983-1990.  Arch Surg. 1992;127(6):694-698. doi:10.1001/archsurg.1992.01420060066010PubMedGoogle ScholarCrossref
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McGonigal  MD, Cole  J, Schwab  CW, Kauder  DR, Rotondo  MF, Angood  PB.  Urban firearm deaths: a five-year perspective.  J Trauma. 1993;35(4):532-536. doi:10.1097/00005373-199310000-00006PubMedGoogle ScholarCrossref
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D’Alessio  JG.  Gunshot wounds: bullet caliber is increasing.  J Trauma. 1999;47(5):992-993.PubMedGoogle ScholarCrossref
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Wintemute  GJ.  The relationship between firearm design and firearm violence: handguns in the 1990s.  JAMA. 1996;275(22):1749-1753. doi:10.1001/jama.1996.03530460053031PubMedGoogle ScholarCrossref
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Kellermann  AL, Lee  RK, Mercy  JA, Banton  J.  The epidemiologic basis for the prevention of firearm injuries.  Annu Rev Public Health. 1991;12:17-40. doi:10.1146/annurev.pu.12.050191.000313PubMedGoogle ScholarCrossref
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Sauaia  A, Gonzalez  E, Moore  HB, Bol  K, Moore  EE.  Fatality and severity of firearm injuries in a Denver trauma center, 2000-2013.  JAMA. 2016;315(22):2465-2467. doi:10.1001/jama.2016.5978PubMedGoogle ScholarCrossref
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Livingston  DH, Lavery  RF, Lopreiato  MC, Lavery  DF, Passannante  MR.  Unrelenting violence: an analysis of 6,322 gunshot wound patients at a level I trauma center.  J Trauma Acute Care Surg. 2014;76(1):2-9. doi:10.1097/TA.0b013e3182ab19e7PubMedGoogle ScholarCrossref
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Kent  AJ, Sakran  JV, Efron  DT, Haider  AH, Cornwell  EE  III, Haut  ER.  Understanding increased mortality after gunshot injury.  Am J Public Health. 2017;107(12):e22-e23. doi:10.2105/AJPH.2017.304100PubMedGoogle ScholarCrossref
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Karlson  TA, Hargarten  SW.  Reducing Firearm Injury and Death: A Public Health Sourcebook on Guns. New Brunswick, NJ: Rutgers University Press; 1997.
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Kleck  G.  Point Blank: Guns and Gun Violence in America. Hawthorne, NY: Aldine de Gruyter; 1997.
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Blackman  PH.  A critique of the epidemiological study of firearms and homicide.  Homicide Stud. 1997;1(2):169-189. doi:10.1177/1088767997001002005Google ScholarCrossref
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Hahn  RA, Bilukha  OO, Crosby  A,  et al. Task Force on Community Preventive Services.  First reports evaluating the effectiveness of strategies preventing violence: firearms laws: findings from the task force on community prevention services.  MMWR Recomm Rep. 2003;52(RR-14):11-20.PubMedGoogle Scholar
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Institute of Medicine and National Research Council.  Priorities for Research to Reduce the Threat of Firearm-Related Violence. Washington, DC: National Academies Press; 2013.
17.
National Research Council.  Firearms and Violence: A Critical Review. Washington, DC: National Academies Press; 2005.
18.
Wolfgang  M.  Patterns in Criminal Homicide. Philadelphia: University of Pennsylvania Press; 1958. doi:10.9783/9781512808728Crossref
19.
Wright  JD, Rossi  PH, Daly  K.  Under the Gun: Weapons, Crime, and Violence in America. Hawthorne, NY: Aldine de Gruyter; 1983.
20.
Zimring  FE.  The medium is the message: firearm caliber as a determinant of death from assault.  J Legal Stud. 1972;1:97-124. doi:10.1086/467479Google ScholarCrossref
21.
Morral  AR, Schell  TL, Tankard  M.  The Magnitude and Sources of Disagreement Among Gun Policy Experts. Santa Monica, CA: RAND Corporation; 2018. doi:10.7249/RR2088.1Crossref
22.
von Elm  E, Altman  DG, Egger  M, Pocock  SJ, Gøtzsche  PC, Vandenbroucke  JP; STROBE Initiative.  The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies.  J Clin Epidemiol. 2008;61(4):344-349. doi:10.1016/j.jclinepi.2007.11.008PubMedGoogle ScholarCrossref
23.
Muller  CJ, MacLehose  RF.  Estimating predicted probabilities from logistic regression: different methods correspond to different target populations.  Int J Epidemiol. 2014;43(3):962-970. doi:10.1093/ije/dyu029PubMedGoogle ScholarCrossref
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Harding  DJ.  Living the Drama: Community, Conflict and Culture Among Inner-City Boys. Chicago, IL: University of Chicago Press; 2010. doi:10.7208/chicago/9780226316666.001.0001Crossref
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Braga  AA, Dusseault  D.  Can homicide detectives improve homicide clearance rates?  Crime Delinq. 2018;64(3):283-315. doi:10.1177/0011128716679164Google ScholarCrossref
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    8 Comments for this article
    EXPAND ALL
    Type of weapon matters
    Frederick Rivara, MD, MPH | University of Washington
    With 14,000 homicides annually from guns, further information on these injuries that might decrease the toll of gun violence is critically important. While the exact location of the GSW is critically important, this study shows that overall the caliber of the bullet also greatly matters.
    CONFLICT OF INTEREST: Editor in Chief, JAMA Network Open
    Difficult to disentangle caliber from multiple hits
    James Cawood, Ph.D. | Factor One, Inc.
    Interesting work. It struck me that since the analysis showed that the fatal cases in this sample involved roughly twice as many wounds on average as the non-fatal cases, the likely additional traumatic and ballistic effects (e.g. blood loss, vital tissue damage, etc.) of those additional wounds raises a significant question concerning what effect the increased caliber had versus the additional effects of the increased number of wounds.
    CONFLICT OF INTEREST: None Reported
    Caliber - Fatal Validity Flaw
    Douglas Goar, PhD | Retired

    The 7.62 x 39 mm caliber is actually a .30 caliber bullet and by the authors' definition should be grouped into the “small caliber” group. This error is a flaw in the validity of your study. It should also be noted that the 7.62 x 39 mm round is a rifle round. It has a much higher muzzle velocity, generally 2 to 3 time that of handgun rounds. Lethality of a round for the most part must include the caliber and muzzle velocity and then remaining energy at distance to the intended target. For example, the Fort Hood shooter used a FN 5.7 handgun which is a .22 caliber round but with a very high muzzle velocity in the neighborhood of 2000 FPS. The lethality of that attack is well documented.

    CONFLICT OF INTEREST: None Reported
    READ MORE
    Definitions of "Caliber" and Firearm Type Problematic
    Dave A. Olsen | None

    It appears the authors are trying to get at some measure of overall measure of a cartridge to determine lethality.

    They conflate caliber (diameter of the projectile), powder charge, type of gun action (revolver vs semi auto) and other things.

    For example, a .38 and .357 magnum fire the same projectile (caliber) but use different powder charges. Same with .40 and 10mm caliber firearms.

    A .44 magnum is fired from a revolver, .40 and .10 mm from a semi automatic.

    The .30 caliber rifle is smaller caliber but the same bullet weight as the .38 and 9 mm bullets and fired from a longer barrel.

    The study does not mention the type of projectile, design, weight, material, shape, and other factors that any hunter would know has a bearing on effectiveness for different uses.

    So, you could arrange the data to show other outcomes.

    The smaller 9mm is more lethal than .40 caliber.

    Revolvers are more lethal than semi automatics (depending on what action the .45 caliber guns used).

    AR15 rifles and their most common cartridge using a .22 caliber bullet are not used for homicides.


    And this only scratches the surface of ballistics, retained energy, sectional density, bullet construction, weight of the gun and its effects on precision, sights, etc. that have an effect on potential lethality.

    Also not mentioned was the number of homicides prevented by the use of firearms by potential victims. Does unholstering a .44 magnum cause crooks to flee more than showing a .22 derringer?

    CONFLICT OF INTEREST: Firearm enthusiast
    READ MORE
    Caliber Also Affects Accuracy
    Adam Peterson | None

    The power of the cartridge has a dramatic effect on the accuracy of the firearm. It is much much harder to place an accurate follow-up shot with a more powerful handgun. Clearly a hit with a powerful bullet will be more deadly than a hit with a weaker one, however you can make more hits with a weaker bullet. The data on the number of shots taken compared to hits isn't as available or as accurate as the data on number and placement of wounds but one currently has an effect on the other and that should have been explored.

    CONFLICT OF INTEREST: None Reported
    Nothing Really New
    John Santry, B.A. | Law Enforcement
    The notion that caliber plays a roll in terminal ballistics has been known for decades. For example, the FBI has known since the late 1980s that bullet performance is critical to stopping a threat. These were lessons learned following the disastrous Miami shootout, and these costly lessons are why American law enforcement officers don't carry .22 caliber pistols. Although, according to the FBI, within the common law enforcement calibers (9mm, 40 Auto, 45 Auto), the most critical factor is penetration, not necessarily bullet diameter. Of course, success in the law enforcement world is measured in stopping a threat, not death. In our world, a bullet wound can stop a threat without causing death and still be considered 100% effective. The problem here is that small calibers (and - by the way - I disagree with how calibers were categorized in this study) do not STOP as well as larger calibers due to a number of factors including the common lack of adequate penetration by small caliber projectiles. I also wish the study included a specific breakdown of wound location by caliber since location is such a critical factor. The element of time is also missing. In other words, how long did it take for first responders to arrive? How long was it before the victim arrived at a trauma center? How much time elapsed between the wound and death? These are all critical questions.

    "Guns don't kill people" refers only to the fact that guns don't have will or intent. The notion that there is any more meaning than that is just silly.

    Finally - although it was probably statistically insignificant - why on earth did the study include 7.62 X 39mm?

    CONFLICT OF INTEREST: None Reported
    READ MORE
    "Most gunshot victims and survivors were young minority men with prior court arraignments."
    Peter Proctor | http://www.drproctor.com
    The preponderance (94%+) of young minority males as both victims and their killers and the apparent connection with both gang activity and the drug trade is in accord with previous findings, including the claims of antigun advocate Michael Bloomberg. By dint of age, criminal record, and engagement in a criminal enterprise, most, perhaps all, cannot legally own firearms.

    Consequently, most of these individuals have very little firearms training and experience. Police tend to frequent gun ranges and there is a paucity of public lands around Boston
    where shooting is legal. Thus, other variables such as bullet caliber come to the fore.

    An old saw among sportsmen is that "Guns don't kill people, proper stance, grip, aim, trigger pull, and follow-through kill people". That is, training counts. Allegedly, gangs on, e.g., the West coast with greater access to private transportation practice gun handling out in the countryside, typically on public lands far away from the public or law-enforcement, and are thus often quite proficient. Such material differences in training may account for much of the variability of the data.
    CONFLICT OF INTEREST: None Reported
    READ MORE
    Complex Topic
    Ross Boyce, MD, MSc | University of North Carolina at Chapel Hill
    Prior to medical school, I served five years as an infantry officer in the United States Army, service that included a deployment to eastern Baghdad in 2004-05 as a Reconnaissance Platoon Leader. Therefore, I imagine I am one of the few physicians who has seen the tragic impact of firearm injuries in our emergency rooms and medical wards, but who has also used a firearm to take the life of another human being in combat. Those seemingly antithetical experiences, rather than any formal research, inform my comments below.

    First, allow me to commend the authors (and the editors) for
    tackling such an urgent, yet divisive issue. However, the fact that our society is so polarized on its approach to gun violence suggests that the two sides don't even agree on basic facts and/or use common language. My concern is that some aspects of this article, especially reference to the very different types of firearms studied, could exacerbate, rather than bridge that divide. After reading the article, I suspect that those advocating for wider availability of guns will dismiss the authors as "naive."

    For example, the discussion of caliber is inconsistent (as pointed out by previous commentors) not only in the classifications, but also in the units used. Caliber is simply the internal diameter of the barrel, which is traditionally measured in hundredths of an inch. Hence a "50 caliber" bullet has a diameter of 0.5 inches or 12.7 mm. Therefore, it is not clear to me how the authors decided on their classification scheme in which a 0.357 magnum (ie 9.06 mm) is coded as "large," yet a 0.38 caliber (9.65 mm) is coded as medium. Similarly, a 7.62 x 39 mm (0.3 caliber) is coded as large, while a 0.32 caliber (8.13 mm) is coded as small. It seems as if the authors are making other assessments about the power (i.e. kinetic energy, muzzle velocity, etc) of the round. I am also surprised that the journal would allow switching back and forth between metric and imperial units so frequently, even if the authors are using common terms.

    Second, I would like to see the analysis either stratified or limited by number of gunshot wounds and wound distribution. For example, I think it would be much more compelling if the authors were able to demonstrate that among individuals who received a single gunshot wound to the chest, those who were shot with larger caliber bullets died more frequently, although I suspect the study is not powered appropriately for outcomes such as this.

    Lastly, I think it would be a mistake to focus on the caliber result, rather than other findings, such as the high proportion of events associated with gang violence and victims of color (ie wealth inequalities, historical discrimination), the much stronger association between fatal outcomes and multiple wounds (ie high capacity weapons), and the overwhelming number of events associated with handguns/pistols as opposed to rifles (ie ability to conceal, transport, etc). These findings seem just as, if not more important, from a policy perspective than any association with caliber.
    CONFLICT OF INTEREST: None Reported
    READ MORE
    Original Investigation
    Public Health
    July 27, 2018

    The Association of Firearm Caliber With Likelihood of Death From Gunshot Injury in Criminal Assaults

    Author Affiliations
    • 1School of Criminology and Criminal Justice, Northeastern University, Boston, Massachusetts
    • 2Sanford Institute of Public Policy, Duke University, Durham, North Carolina
    JAMA Network Open. 2018;1(3):e180833. doi:10.1001/jamanetworkopen.2018.0833
    Key Points

    Question  Is there an association between the likelihood of death for firearms shooting victims and the caliber of the firearm?

    Findings  A cross-sectional study using 5 years of data extracted from investigation files kept by the Boston Police Department determined that the case-fatality rates of assaults inflicting gunshot injury increased significantly with the caliber of the firearm. Caliber was not significantly correlated with other observable characteristics of the assault, including indicators of intent and determination to kill.

    Meaning  The findings are foundational to the debate over whether deadly weapons should be better regulated and provide evidence against the common view that whether the victim lives or dies is determined largely by the assailant’s intent and not the type of weapon.

    Abstract

    Importance  A foundational issue in firearms policy has been whether the type of weapon used in an assault affects the likelihood of death.

    Objective  To determine whether the likelihood of death from gunshot wounds inflicted in criminal assaults is associated with the power of the assailant’s firearm as indicated by its caliber.

    Design, Setting, and Participants  Cross-sectional study with multivariate analysis of data on shooting cases extracted by the authors from police investigation files for assaults that took place in Boston, Massachusetts, between January 1, 2010, and December 31, 2014. These data were analyzed between October 1, 2017, and February 18, 2018. In all cases the victim sustained 1 or more gunshot wounds in circumstances that the Boston Police Department deemed criminal. The working sample included all 221 gun homicides and a stratified random sample of 300 nonfatal cases drawn from the 1012 that occurred during the 5-year period. Seven nonfatal cases were omitted because they had been misclassified.

    Exposures  The primary source of variation was the caliber of the firearm used to shoot the victim.

    Main Outcomes and Measures  Whether the victim died from the gunshot wound(s).

    Results  The final sample of 511 gunshot victims and survivors (n = 220 fatal; n = 291 nonfatal) was predominantly male (n = 470 [92.2%]), black (n = 413 [80.8%]) or Hispanic (n = 69 [13.5%]), and young (mean [SD] age, 26.8 [9.4] years). Police investigations determined firearm caliber in 184 nonfatal cases (63.2%) and 183 fatal cases (83.2%). These 367 cases were divided into 3 groups by caliber: small (.22, .25, and .32), medium (.38, .380, and 9 mm), or large (.357 magnum, .40, .44 magnum, .45, 10 mm, and 7.62 × 39 mm). Firearm caliber had no systematic association with the number of wounds, the location of wounds, circumstances of the assault, or victim characteristics, as demonstrated by χ2 tests of each cluster of variables and by a comprehensive multinomial logit analysis. A logit analysis of the likelihood of death found that compared with small-caliber cases, medium caliber had an odds ratio of 2.25 (95% CI, 1.37-3.70; P = .001) and large caliber had an odds ratio of 4.54 (95% CI, 2.37-8.70; P < .001). Based on a simulation using the logit equation, replacing the medium- and large-caliber guns with small-caliber guns would have reduced gun homicides by 39.5%.

    Conclusions and Relevance  Firearms caliber was associated with the likelihood of death from gunshot wounds in criminal assault. Shootings with larger-caliber handguns were more deadly but no more sustained or accurate than shootings with smaller-caliber handguns. This conclusion is of direct relevance to the design of gun policy.

    Introduction

    In 1 of 6 cases of criminal assault inflicting a gunshot wound, the victim dies.1 Whether any such shooting proves fatal is determined by the number and location of wounds and by the size and weight of the bullets, among other variables.2,3 Systematic studies of gunshot wound severity have documented trends associated with the mix of firearms commonly used in assaults.4,5 Of particular concern in the 1980s and early 1990s was the rapid shift from revolvers to semiautomatic pistols and from smaller caliber to medium and larger caliber.6,7 The pistols were more powerful and enabled the shooter to fire a large number of rounds rapidly, increasing the chance of multiple wounds.6-8 While speculative, recent studies suggest a continuing trend toward greater wound severity associated with the greater power of firearms in common use.9,10 (Improved trauma care may have prevented an increase in the national case-fatality rate.11) It is widely accepted among medical and public health professionals that the likelihood of death in an assault increases with the power of the gun.2,3,6-8,12 But that belief is routinely challenged by advocates and some social scientists in the national debate over gun regulation.13,14

    The opposing view holds that it is not the type of weapon that determines whether the victim lives or dies, but rather the intent of the assailant.13-17 This notion is captured by the old slogan “guns don’t kill people; people kill people.” In this view, an assailant who is determined to kill will do what is necessary to accomplish that purpose, regardless of weapon type.11-19 As a logical corollary, the 1 in 6 who die from a gun assault differ from those who survive with respect to the shooter’s intent and determination. In effect, the criminal law and the courts conform with this view by treating a fatal shooting as a more serious crime than a nonfatal shooting. The outcome of the shooting (life or death) is viewed as a reliable guide to the intent—the determination to kill—of the shooter. The most severe punishments, including the death penalty and life in prison, are reserved for cases in which the victim dies.

    In 1972, Franklin Zimring published a seminal article that challenged the belief that the outcome of the shooting was primarily determined by the intent of the shooter.20 He found that nonfatal and fatal shootings were very similar with respect to the circumstances and observed characteristics of the victims and assailants. In effect, the survivors were “lucky” in that in many cases a small change in the path of the bullet would have resulted in the victim’s death. A notable pattern in Zimring’s data was that the likelihood of death was correlated with the caliber of the assailant’s firearm. He concluded that the outcome of gun assaults had a large random element, and that the power of the firearm was one systematic factor influencing the likelihood that an individual with a gunshot injury would survive, a phenomenon he dubbed “instrumentality.” The contrary view is that the caliber of the gun is simply a reflection of the assailant’s determination to kill, with little independent influence on the probability of death.11-19

    The importance of instrumentality in the gun debate is illustrated by findings from a recent survey of experts by the RAND Corporation. Respondents were asked to estimate the effect on the overall homicide rate of a policy that was successful in reducing the firearms homicide rate. Those respondents who on other items had favored permissive firearms regulation tended to believe that assailants would substitute other weapons with nearly the same effect, unlike those respondents who favored more restrictive regulations: “Median responses by the permissive class suggested that 90 percent of prevented firearm homicides would end as a homicide by another means, and median responses by the restrictive class estimated that just 20 percent would. The middle 50 percent of responses from each group (ie, between the 25th and 75th percentile) did not overlap.”21

    The relative importance of chance vs intention in determining the likelihood of death cannot be measured because there is no direct measure of intention in available data. But if Zimring is correct that the caliber of the gun in an assault is not correlated with systematic factors such as the skill and determination of the assailant, then the pattern of case-fatality rates across calibers provides a clean test of instrumentality, akin to an experiment.

    This study follows the original Zimring analysis but with better data and more sophisticated statistical techniques.

    Methods

    Official incident reports for 221 homicides and 1012 nonfatal gun assaults where victims and survivors sustained gunshot wounds were accessed through the Boston Police Department (BPD). These represent all cases known to the BPD for the period January 1, 2010, to December 31, 2014, that were deemed to be criminal by the BPD (not justified or self-inflicted). The research team did not have the resources to code all of the nonfatal cases, and instead selected a stratified random sample of 300 gunshot survivors by randomly selecting 60 survivors per year. Of the selected cases, 1 was excluded because the event did not occur in the BPD’s jurisdiction, and 6 were excluded because it was determined that the individual had not been shot. One gun homicide and 2 nonfatal assaults were committed with shotguns and excluded from the study because of the difficulty of comparing the type of wounds generated by the multiple pellets of a shotgun blast with those created by bullets. The final nonfatal shooting survivor sample included 291 individuals and the final fatal shooting victim sample included 220 individuals.

    The institutional review board at Northeastern University approved the study with the requirement that gunshot victim and survivor identities were kept confidential by the removal of all personal identifying information (informed consent from the participants was not required). The study conforms with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cross-sectional research studies.22

    The research team attempted to acquire detailed information on the 511 fatal and nonfatal shootings by interviewing investigators and reviewing incident reports and detective case files (including emergency medical response and coroner reports). The case files for the homicide victims were generally complete in recording number and location of wounds, but some of the files for nonfatal cases were missing this information. Furthermore, some homicide and assault cases were missing data on firearm caliber, either because cartridge and bullet fragments were not recovered, or if recovered were too damaged to make a determination of the specific caliber. For analyses requiring data on caliber, the working sample included 367 cases (184 nonfatal and 183 fatal). There were no systematic differences between cases included in the analysis and those excluded because of absence of caliber data (eTable 1 in the Supplement).

    Statistical Analysis

    Descriptive statistics were used to compare the characteristics of fatal and nonfatal criminal shootings with respect to the demographic characteristics of gunshot victims and survivors, the circumstances of the assault, and other variables. Multivariate binary and multinomial logistic regression models were used to estimate the relationship between a categorical outcome variable and a predictor variable, holding the influence of other variables constant. The conventional 2-tailed .05 level of significance was selected as the benchmark to reject the null hypothesis of no difference in the association between variables. Missing data for caliber and wounds were analyzed using multivariate logistic regression to ascertain if missingness was systematic or as good as random (eTable 2 in the Supplement).

    The primary analysis, which uses the working sample, had 3 goals. The first goal was to determine whether caliber is statistically independent of observable characteristics of the assault, including indicators of skill and intent, to validate the claim that caliber serves as a natural experiment for testing instrumentality. We used χ2 tests to compare caliber with each cluster of variables (demographic characteristics of the victim, circumstances of the assault, neighborhood in which the assault occurred, whether it was indoors or outdoors, number of shots fired, and number and location of wounds). In addition, a multinomial logit equation was estimated with all these covariates included.

    The second goal was to use this natural experiment to estimate the causal relationship between caliber of the assailant’s firearm and likelihood that the victim died. The third goal, building on the second, was to estimate the effect of a hypothetical intervention, namely replacing all the medium- and large-caliber guns with small-caliber guns. Using the logit regression equation on outcome as the basis for the simulation, the probability of death was calculated for each assault (and then averaged) under both the observed calibers (small, medium, and large) and the hypothetical case of replacing all larger calibers with small.23 The percentage reduction in fatalities (homicides) was a measure of the overall effect of instrumentality associated with caliber for our sample.

    It should be noted that the probabilities of death reflect the fact that the nonfatal shootings are a sample of the total, whereas nearly all homicides are included. Hence the computed probabilities are a multiple of the true probabilities of death. But the ratio of estimated probabilities should be unaffected, as the multiple is the same for the numerator and denominator of the ratio.

    In all analyses, caliber was coded as either small (.22, .25, and .32), medium (.38, .380, and 9 mm), or large (.357 magnum, .40, .44 magnum, .45, 10 mm, and 7.62 × 39 mm). The wound location was coded as head or neck; chest, back, or abdomen; or arms and legs. The number of wounds was coded as 1 or more than 1.

    Stata SE 14.1 statistical software (StataCorp) was used to calculate the maximum likelihood estimates of the parameters for the predictor variables and to compute the associated probability values. In line with current best practice, robust standard errors were used, clustered by police district. Policing districts were used as indicators for Boston neighborhoods to capture both variations in community contexts and local policing practices that could affect the lethality of shootings and the quality of investigative information.24,25

    Results

    Table 1 presents the characteristics of gunshot victims and survivors and circumstances in gun assaults and homicides occurring in Boston between January 1, 2010, and December 31, 2014. The final sample of 511 gunshot victims and survivors (220 fatal and 291 nonfatal) was predominantly male (n = 470 [92.2%]), black (n = 413 [80.8%]) or Hispanic (n = 69 [13.5%]), and young (mean [SD] age, 26.8 [9.4] years). The fatal and nonfatal cases have very similar distributions across each variable, including victim and survivor sex, race/ethnicity, age, and criminal history; circumstances that led to the shooting; and police district. For only 1 variable is there a statistically significant difference between fatal and nonfatal cases, and that is whether the shooting occurred indoors or outdoors. Fatal shootings were more likely to occur indoors (54 of 220 [24.5%]) relative to nonfatal shootings (39 of 291 [13.4%]), with a difference of 11.1 percentage points (95% CI, 4.2%-18.0%; P = .001). Most gunshot victims and survivors were young minority men with prior court arraignments. Most attacks occurred in circumstances where gangs or drugs played an important role (according to BPD investigation results). Most were in outdoor locations in the disadvantaged Boston neighborhoods of Roxbury, Mattapan, and Dorchester.

    Table 2 reports the distribution of calibers, shots fired, number of gunshot wounds, and wound location for nonfatal and fatal cases. Police investigations determined firearm caliber in 184 nonfatal cases (63.2%) and 183 fatal cases (83.2%). Most interpersonal gun violence involves handguns, and Boston is no exception. Only 1 gun homicide was committed with a rifle caliber (7.62 × 39 mm fired from an AK-47 assault rifle). The most common caliber was 9 mm in both nonfatal shootings (50 of 184 [27.2%]) and gun homicides (65 of 183 [35.6%]). Homicides were more likely to involve large-caliber firearms (60 of 183 [32.8%]) relative to nonfatal shootings (33 of 184 [17.9%]).

    The number of shots fired in each case was estimated by the BPD based on spent bullets and cartridge casings recovered at the crime scene. The mean (SD) number of shots was higher in fatal shootings (6.11 [5.73]) than in nonfatal shootings (4.41 [3.98]). Homicide victims were more likely to have multiple gunshot wounds (119 of 183 [65.0%]) than were nonfatal shooting survivors (50 of 184 [27.2%]), and the mean (SD) number of gunshot wounds for homicide victims was correspondingly higher than the number for survivors (2.82 [2.76] vs 1.67 [1.41], respectively). A separate calculation found that the number of shots fired was statistically unrelated to caliber for both fatal and nonfatal cases (eTable 3 in the Supplement).

    The distributions of wound locations differed in the expected way. For individuals with a single wound, 84 of 134 (62.7%) were peripheral (legs, arms, or shoulders) for nonfatal cases, compared with only 1 of 64 (1.6%) for fatal cases. For individuals with multiple wounds, the most serious wound was peripheral in 18 of 50 nonfatal shootings (36.0%) compared with 1 of 119 fatal shootings (0.8%). (The ranking used to determine seriousness was based only on location, with head and neck most serious; then chest, back, and abdomen; then arms, shoulders, and legs.

    Table 3 provides results relevant to the first goal of the analysis. It presents the results of a multinomial logistic regression on the caliber of the gun used in the assault. In model 1, the variables include the sex, race, and age of the victim or survivor, the circumstances (motivation) of the attack, and whether the attack occurred indoors or outdoors. Model 2 adds additional covariates, including the number of wounds and location of the most serious wounds (both considered indicators of skill and determination to kill). There are no statistically significant results for either model. Supplemental χ2 analyses of association of caliber with victim or survivor and shooting characteristics also yielded statistically nonsignificant results, confirming the results of the multivariate analysis (eTable 4 in the Supplement). The lack of systematic association is what would be expected if caliber were assigned at random, as in an experiment.

    Table 4 presents the results of a multivariate logistic regression on whether the event was fatal or nonfatal. The effects of caliber on odds of death are estimated, controlling for gunshot victim and survivor characteristics, whether the shooting occurred indoors or outdoors, and neighborhood indicators (included, not shown). Relative to shootings involving small-caliber firearms (reference category), the odds of death if the gun was large caliber were 4.5 times higher (OR, 4.54; 95% CI, 2.37-8.70; P < .001) and, if medium caliber, 2.3 times higher (OR, 2.25; 95% CI, 1.37-3.70; P = .001). The odds of death in indoor shootings were 2.6 times higher than in outdoor shootings (OR, 2.55; 95% CI, 1.79-3.64; P < .001). The effects of caliber size and indoor location remained strong in the alternate specifications in models 2 and 3. None of the other covariates had a statistically discernible effect on the odds of death.

    The overall effect of larger caliber on deaths can be estimated by simulation using the logit regression results in Table 4. The simulation uses the 367 shooting cases (184 nonfatal [63.2%] and 183 fatal [83.2%]) with known caliber. First, the predicted probability of death for each shooting case was computed using the actual caliber (mean [SD] probability, 0.499 [0.154]), and then the predicted probability on the assumption that all shootings had been with a small-caliber gun (mean [SD] probability, 0.302 [0.137]). The ratio of mean probabilities was 0.605. The implication is that if the medium- and large-caliber guns had been replaced with small caliber (assuming everything else unchanged), the result would have been a 39.5% reduction in gun homicides.

    Discussion

    In a pioneering article published in 1972, Franklin Zimring sought to demonstrate that the type of weapon used in a criminal assault had a causal effect on the likelihood that the victim would die.20 He compiled a data set that allowed him to compare the case fatality rates for criminal shootings by caliber of weapon, which he asserted was a sort of “natural experiment.” He demonstrated that fatality rate was positively correlated with caliber and argued that this gradient was a direct reflection of the intrinsic power and lethality of the weapon. In this article we revisit his analysis with more complete data and more sophisticated statistical methods. We were able to confirm the strong positive association between caliber and fatality rate and summarize the overall effect of larger calibers by simulating the effect on outcomes if all the guns had been small caliber. The result is a 39.5% reduction in the probability of death, implying an equal reduction in the gun homicide rate if the same shootings had occurred but with small-caliber weapons, rather than the actual mix of small, medium, and large calibers.

    That result suggests that the instrumentality effect is large even if the analysis is limited to gun caliber. It would also be of interest to quantify the effect of replacing guns of all types with other commonly available weapons. Presumably the effects would be still larger, although the precise nature of the substitution would have to be specified.

    Limitations

    The main challenge to the results in the current analysis is the possibility that shooters who used large-caliber guns, in comparison with those who used smaller-caliber guns, were somehow more determined to kill or more skillful at killing in ways that are not well measured by the number and location of wounds. That possibility is created by the fact that guns are not randomly assigned to shooters. But we demonstrated that just as if there were random assignment, caliber was uncorrelated with all observable aspects of the shootings except whether the wounded person lived or died.

    There are other limitations of this study. First, caliber was not available for all shootings. We found no statistical pattern of missingness within each of the 2 categories of fatal and nonfatal, but that does not completely settle the issue. Second, the study is limited to the criminal shootings known to the police in a particular time and place.

    Conclusions

    Whether the type of weapon matters in affecting the outcome of a shooting is a foundational issue in the debate over appropriate gun regulation. The results here support the view that the intrinsic power and lethality of the weapon had a direct effect on the likelihood that a victim of a criminal shooting died. For Boston, in the period studied here, simply replacing larger-caliber guns with small-caliber guns with no change in location or number of wounds would have reduced the gun homicide rate by 39.5%. It is plausible that larger reductions would be associated with replacing all types of guns with knives or clubs.

    The finding that the type of weapon is associated with fatality rate provides insight into the nature of homicide. Whether the victim of a serious assault lives or dies is to a large extent a matter of chance, rather than a question of the assailant’s intent. The probability of death is connected to the intrinsic power and lethality of the weapon. That suggests that effective regulation of firearms could reduce the homicide rate. That conclusion is relevant to the national debate over gun regulation, although insufficient in itself to demonstrate that any particular regulation would satisfy a cost-benefit test.

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    Article Information

    Accepted for Publication: April 30, 2018.

    Published: July 27, 2018. doi:10.1001/jamanetworkopen.2018.0833

    Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2018 Braga AA et al. JAMA Network Open.

    Corresponding Author: Anthony A. Braga, PhD, School of Criminology and Criminal Justice, Northeastern University, 360 Huntington Ave, Boston, MA 02115 (a.braga@northeastern.edu).

    Author Contributions: Drs Braga and Cook had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: All authors.

    Acquisition, analysis, or interpretation of data: All authors.

    Drafting of the manuscript: All authors.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: All authors.

    Obtained funding: Braga.

    Administrative, technical, or material support: Braga.

    Supervision: Braga.

    Conflict of Interest Disclosures: Dr Braga reported grants from the US Bureau of Justice Assistance during the conduct of the study. No other disclosures were reported.

    Funding/Support: This work was supported by the US Bureau of Justice Assistance (grant 2011-DB-BX-0014).

    Role of the Funder/Sponsor: The US Bureau of Justice Assistance had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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