Here is a link to a paper by Carlisle Moody, Department of Economics, College of William and Mary.
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Here are some excerpts.
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AbstractThe fact that an individual is willing to commit the most serious crime that carries with it the most serious punishment means that that person is unlikely to be deterred by laws with less serious consequences. This situation is compounded by the fact that many multiple victim public shooters are expecting, even planning, to die in the commission of their crimes. Combining newly developed and traditional difference-in-differences methodologies, we analyze several policies that have been suggested as possibly effective in reducing deaths due to mass public shootings. We find that none of the proposed policies significantly reduce such deaths. However, we find evidence that mass public shooting deaths are lower in places that allow the carrying of concealed firearms.
1. Introduction
Mass public shooting incidents are rare but horrifying events. Such incidents receive intense media coverage and become political events leading to demands that we do something. The obvious question is what should we do? The fact that an individual is willing to commit the most serious crime that carries with it the most serious punishment, life in prison or execution, means that that person is unlikely to be deterred by laws with less serious consequences. This situation is compounded by the fact that many of the shooters are expecting, even planning, to die in the commission of their crimes (Note 1). We analyze several policies that have been found to be effective, or suggested as possibly effective, in reducing deaths due to mass public shootings.
Most of the studies of mass public shootings have employed state-level panel datasets using Two-Way Fixed-Effects (TWFE) regressions with state and year fixed effects. Such regressions have recently been criticized by econometricians studying difference-in-differences analysis. For example, deChaisemartin and D‟Haultfoeuille (2020), henceforth CD, show that the sign of the difference-in-differences coefficient estimated using fixed-effects regression could so biased that the coefficient is negative when all the effects are positive. This finding potentially invalidates nearly all previous analyses concerning the effect of gun laws on deaths due to mass public shootings. Fortunately, CD and others have developed a new methodology which generates unbiased estimates of the difference-in-differences. To our knowledge, this is the first study to use this new methodology to investigate the efficacy of state laws with respect to reducing deaths due to mass public shootings.
The first analysis of mass public shootings was by Lott and Landis (1999) arguing that citizens carrying concealed weapons could deter such attacks because potential shooters would not know who might shoot back. In that study the authors studied multiple victim public shootings defined as two or more people killed, except for the perpetrator, in a public place, although they also considered alternative definitions with more people killed. They excluded incidents, “… that were the byproduct of another crime (e.g., a robbery or drug deal); shootings that involved gang activity (e.g., drive-by shootings); professional hits or shootings related to organized crime; and serial killings or killings that took place over the span of more than one day” (Lott & Landis, 1999, p. 7). A Lexis/Nexis search found 931 cases over the period 1977-1995. Using a Tobit regression, they found that Right-To-Carry (RTC) laws significantly reduced the number of mass public shootings, the number killed, and the number injured. They also found that waiting periods, firearm enhancement laws, and background checks had no significant effect on the number of mass public shootings or the harm they cause.
Duwe, Kovandzic, and Moody (2002), using a combination of FBI Supplemental Homicide Reports (SHR) and Lexis/Nexis searches, identified 116 mass public shootings between 1976 and 1999, defined as four or more people killed, apart from the shooter, but including some that occurred during the commission of a crime. Using the negative binomial model on this more restrictive definition, they found that RTC laws had negative but insignificant effects on the number of incidents, the number killed, and the number wounded.
Gius (2015) using Mother Jones and SHR data, estimated the effects of federal and state assault weapons bans for the years 1982-2011, finding evidence that such bans significantly reduced fatalities in mass shootings. Gius (2018) found that state assault weapon bans were associated with lower fatalities in school shootings.
Using data compiled by the Congressional Research Service, Fox and Fridel (2016) found that mass public shooting incidents were not significantly reduced during the Federal assault weapon ban from 1994-2004. However, Klarevas, Conner, and Hemenway (2018) found that bans on large capacity magazines (LCM, more than 10 rounds), including the 1994 Federal assault weapons ban which included an LCM ban, were associated with a significant reduction in the number of incidents and the number of fatalities in mass shootings where six or more people are killed. DiMaggio, Avraham, Berry, Bukur, Feldman, and Klein (2019), using linear and Poisson regression on national data, also found that the Federal assault weapons ban significantly reduced the number of mass public shootings. The authors used data from three sources, but according to Webster, McCourt, Crifasi, Booty, and Stuart (2020, p. 173),
Inexplicably, the researchers only included cases in their analyses that appeared in all three sources and thereby excluded many incidents of fatal mass shootings. This limited their data to only 51 public mass shootings that presumably were the most widely publicized. The study did not examine variation by state and thus did not consider state gun laws nor did it control for other covariates other than [a] linear trend.
Koper (2020) finds that mass public shootings in which the shooter used large capacity magazines result in more fatalities than those incidents where shooters did not use LCM‟s. He estimates that LCM bans, if effective, could reduce the number of mass shooting fatalities by 11-15 percent. Reeping, Cerdá, Kalesan, Wiebe, Galea, and Branas (2019) using SHR data find that states with more firearms and more permissive firearm laws have more mass shootings. However, SHR data misses many mass-shooting events, including Newtown, CT and Aurora, CO (Webster et al., 2020, pp. 172-173). On the other hand, Lin, Fei, Barzman, and Hossain (2018) using Mother Jones data, find no association between gun ownership or permissive gun laws and the number of fatal mass public shootings. Siegel, Goder-Reiser, Duwe, Rocque, Fox, and Fridel (2020) constructed a database of 143 incidents of mass public shootings of four or more fatalities from 1976-2018 using a variety of sources including SHR and media reports. The authors have made their data available online and we use it in this analysis. They analyze the effect of several policies: large capacity magazine bans, assault weapons bans, permit-to-purchase laws, red flag laws, universal background checks, may-issue laws (states without right to carry or permit-less carry laws), relinquishment laws (confiscating guns from individuals that become prohibited from owning firearms), and violent misdemeanor laws (prohibiting individuals from owning firearms who commit a variety of non-felony crimes). They find two of these policies have significant effects. Permit-to-purchase laws are found to significantly reduce the number of mass public shootings but have no significant effect on the number of fatalities associated with those shootings. On the other hand, state large capacity magazine bans are found to significantly reduce fatalities but have no significant effect on the number of incidents. A serious drawback to this analysis is that, although it is a panel data of state-years, the authors do not use state fixed-effects to correct for unobserved heterogeneity. As a result, the estimates are biased due to the correlation between the number and severity of mass shootings and unobserved time-invariant factors such as climate, culture, history, political attitudes, etc.
Webster et al. (2020) analyze a data set created by supplementing SHR data with data from the Stanford Mass Shootings in America and the Gun Violence Policy data sets. The threshold is four or more victims, not counting the shooter. They exclude gang-related and crime-related mass shootings but include domestic violence mass shootings as a separate category. They find that permit-to-purchase laws significantly reduce both the number of incidents and the number of fatalities associated with mass shootings. In the robustness section, they also find that LCM bans significantly reduce incidents and fatalities. Because of reporting difficulties with the SHR, they do not include observations from Florida, Kansas, Kentucky, Nebraska, and Montana. These omissions are problematic because both the Stanford and Gun Violence Policy datasets include both SHR and media search data, obviating the need to omit any states.
Thus, there is some evidence that permit-to-purchase laws, large capacity magazine bans, and assault weapons bans are effective in reducing deaths from mass public shootings. There is little support for any other gun control laws in this literature. Nevertheless, a cursory search of the internet on “mass shootings” and related phrases finds many other suggestions for reducing the death toll associated with mass shootings. Many sites suggest that universal background checks might be successful. Since many mass shooters, especially school shooters are quite young, some sites suggested that safe storage laws and bans on juveniles possessing firearms might be effective. Since many mass shooters are willing or committed to die in the act, policies designed to reduce suicide in general could reduce the number of people who adopt mass shooting as their suicidal act (Note 2). On the other hand, conservative, gun-rights, and libertarian sites suggest that right-to-carry laws and permit-less carry (also known as constitutional carry) laws would encourage ordinary citizens to carry concealed handguns, allowing them to intervene before police arrive. There is also some evidence that shooters tend to choose places that forbid firearms on the premises, presumably to reduce the probability of potential victims returning fire. If so, it is possible that reducing the number of these “gun-free zones” could save lives (Note 3).
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Discussion
1. Introduction
Mass public shooting incidents are rare but horrifying events. Such incidents receive intense media coverage and become political events leading to demands that we do something. The obvious question is what should we do? The fact that an individual is willing to commit the most serious crime that carries with it the most serious punishment, life in prison or execution, means that that person is unlikely to be deterred by laws with less serious consequences. This situation is compounded by the fact that many of the shooters are expecting, even planning, to die in the commission of their crimes (Note 1). We analyze several policies that have been found to be effective, or suggested as possibly effective, in reducing deaths due to mass public shootings.
Most of the studies of mass public shootings have employed state-level panel datasets using Two-Way Fixed-Effects (TWFE) regressions with state and year fixed effects. Such regressions have recently been criticized by econometricians studying difference-in-differences analysis. For example, deChaisemartin and D‟Haultfoeuille (2020), henceforth CD, show that the sign of the difference-in-differences coefficient estimated using fixed-effects regression could so biased that the coefficient is negative when all the effects are positive. This finding potentially invalidates nearly all previous analyses concerning the effect of gun laws on deaths due to mass public shootings. Fortunately, CD and others have developed a new methodology which generates unbiased estimates of the difference-in-differences. To our knowledge, this is the first study to use this new methodology to investigate the efficacy of state laws with respect to reducing deaths due to mass public shootings.
The first analysis of mass public shootings was by Lott and Landis (1999) arguing that citizens carrying concealed weapons could deter such attacks because potential shooters would not know who might shoot back. In that study the authors studied multiple victim public shootings defined as two or more people killed, except for the perpetrator, in a public place, although they also considered alternative definitions with more people killed. They excluded incidents, “… that were the byproduct of another crime (e.g., a robbery or drug deal); shootings that involved gang activity (e.g., drive-by shootings); professional hits or shootings related to organized crime; and serial killings or killings that took place over the span of more than one day” (Lott & Landis, 1999, p. 7). A Lexis/Nexis search found 931 cases over the period 1977-1995. Using a Tobit regression, they found that Right-To-Carry (RTC) laws significantly reduced the number of mass public shootings, the number killed, and the number injured. They also found that waiting periods, firearm enhancement laws, and background checks had no significant effect on the number of mass public shootings or the harm they cause.
Duwe, Kovandzic, and Moody (2002), using a combination of FBI Supplemental Homicide Reports (SHR) and Lexis/Nexis searches, identified 116 mass public shootings between 1976 and 1999, defined as four or more people killed, apart from the shooter, but including some that occurred during the commission of a crime. Using the negative binomial model on this more restrictive definition, they found that RTC laws had negative but insignificant effects on the number of incidents, the number killed, and the number wounded.
Gius (2015) using Mother Jones and SHR data, estimated the effects of federal and state assault weapons bans for the years 1982-2011, finding evidence that such bans significantly reduced fatalities in mass shootings. Gius (2018) found that state assault weapon bans were associated with lower fatalities in school shootings.
Using data compiled by the Congressional Research Service, Fox and Fridel (2016) found that mass public shooting incidents were not significantly reduced during the Federal assault weapon ban from 1994-2004. However, Klarevas, Conner, and Hemenway (2018) found that bans on large capacity magazines (LCM, more than 10 rounds), including the 1994 Federal assault weapons ban which included an LCM ban, were associated with a significant reduction in the number of incidents and the number of fatalities in mass shootings where six or more people are killed. DiMaggio, Avraham, Berry, Bukur, Feldman, and Klein (2019), using linear and Poisson regression on national data, also found that the Federal assault weapons ban significantly reduced the number of mass public shootings. The authors used data from three sources, but according to Webster, McCourt, Crifasi, Booty, and Stuart (2020, p. 173),
Inexplicably, the researchers only included cases in their analyses that appeared in all three sources and thereby excluded many incidents of fatal mass shootings. This limited their data to only 51 public mass shootings that presumably were the most widely publicized. The study did not examine variation by state and thus did not consider state gun laws nor did it control for other covariates other than [a] linear trend.
Koper (2020) finds that mass public shootings in which the shooter used large capacity magazines result in more fatalities than those incidents where shooters did not use LCM‟s. He estimates that LCM bans, if effective, could reduce the number of mass shooting fatalities by 11-15 percent. Reeping, Cerdá, Kalesan, Wiebe, Galea, and Branas (2019) using SHR data find that states with more firearms and more permissive firearm laws have more mass shootings. However, SHR data misses many mass-shooting events, including Newtown, CT and Aurora, CO (Webster et al., 2020, pp. 172-173). On the other hand, Lin, Fei, Barzman, and Hossain (2018) using Mother Jones data, find no association between gun ownership or permissive gun laws and the number of fatal mass public shootings. Siegel, Goder-Reiser, Duwe, Rocque, Fox, and Fridel (2020) constructed a database of 143 incidents of mass public shootings of four or more fatalities from 1976-2018 using a variety of sources including SHR and media reports. The authors have made their data available online and we use it in this analysis. They analyze the effect of several policies: large capacity magazine bans, assault weapons bans, permit-to-purchase laws, red flag laws, universal background checks, may-issue laws (states without right to carry or permit-less carry laws), relinquishment laws (confiscating guns from individuals that become prohibited from owning firearms), and violent misdemeanor laws (prohibiting individuals from owning firearms who commit a variety of non-felony crimes). They find two of these policies have significant effects. Permit-to-purchase laws are found to significantly reduce the number of mass public shootings but have no significant effect on the number of fatalities associated with those shootings. On the other hand, state large capacity magazine bans are found to significantly reduce fatalities but have no significant effect on the number of incidents. A serious drawback to this analysis is that, although it is a panel data of state-years, the authors do not use state fixed-effects to correct for unobserved heterogeneity. As a result, the estimates are biased due to the correlation between the number and severity of mass shootings and unobserved time-invariant factors such as climate, culture, history, political attitudes, etc.
Webster et al. (2020) analyze a data set created by supplementing SHR data with data from the Stanford Mass Shootings in America and the Gun Violence Policy data sets. The threshold is four or more victims, not counting the shooter. They exclude gang-related and crime-related mass shootings but include domestic violence mass shootings as a separate category. They find that permit-to-purchase laws significantly reduce both the number of incidents and the number of fatalities associated with mass shootings. In the robustness section, they also find that LCM bans significantly reduce incidents and fatalities. Because of reporting difficulties with the SHR, they do not include observations from Florida, Kansas, Kentucky, Nebraska, and Montana. These omissions are problematic because both the Stanford and Gun Violence Policy datasets include both SHR and media search data, obviating the need to omit any states.
Thus, there is some evidence that permit-to-purchase laws, large capacity magazine bans, and assault weapons bans are effective in reducing deaths from mass public shootings. There is little support for any other gun control laws in this literature. Nevertheless, a cursory search of the internet on “mass shootings” and related phrases finds many other suggestions for reducing the death toll associated with mass shootings. Many sites suggest that universal background checks might be successful. Since many mass shooters, especially school shooters are quite young, some sites suggested that safe storage laws and bans on juveniles possessing firearms might be effective. Since many mass shooters are willing or committed to die in the act, policies designed to reduce suicide in general could reduce the number of people who adopt mass shooting as their suicidal act (Note 2). On the other hand, conservative, gun-rights, and libertarian sites suggest that right-to-carry laws and permit-less carry (also known as constitutional carry) laws would encourage ordinary citizens to carry concealed handguns, allowing them to intervene before police arrive. There is also some evidence that shooters tend to choose places that forbid firearms on the premises, presumably to reduce the probability of potential victims returning fire. If so, it is possible that reducing the number of these “gun-free zones” could save lives (Note 3).
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Discussion
Using the latest difference-in-differences analyses and fixed-effects negative binomial regressions, we tested nine gun-related policies and four traditional crime-control policies. Despite the findings in previous studies that permit to purchase laws and large capacity magazine bans may be effective, we find that neither these, nor the other policies investigated in this study can be shown to be effective in reducing the number of people killed in mass public shootings. This result might be expected because criminals who are willing to commit the most heinous crime and who are also willing to die in the commission of that crime, are unlikely to be deterred by a safe storage law, for example. On the other hand, there is evidence that increasing the number of places where ordinary citizens are allowed to carry concealed weapons could reduce the number of mass shooting fatalities.
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