Supplementary Appendix

Transcription

1 Supplementary Appendix This appendix has been provided by the authors to give readers additional information about their work. Supplement to: Jena AB, Olenski AR. Reduction in firearm injuries during NRA annual conventions. N Engl J Med 2018;378: DOI: /NEJMc (PDF updated March 2, 2018.)

2 ONLINE SUPPLEMENT Table of Contents Additional background and motivation (page 2) Additional information on databases and methods (page 3) Additional results (page 6) Additional discussion and limitations of findings (page 8) Table S1: NRA Annual Meetings Dates and Locations (page 12) Table S2: Characteristics of the study population (page 13) Table S3: Subgroup analyses of firearm injuries during NRA annual convention dates and control dates (page 14) Table S4: Subgroup analyses of firearm injuries during NRA annual convention dates and control dates using a ±4 week control period (page 15) Table S5: Characteristics of victims and offenders in National Incident-Based Reporting System (NIBRS) (page 16) Figure S1: Unadjusted firearm injuries among commercially insured individuals on dates of NRA annual meetings and control dates during (page 17) Figure S2: Adjusted proportion of crimes involving a firearm on dates of NRA annual conventions and control dates during (page 18) 1

3 This online supplement provides additional information regarding the manuscript, including further background and motivation behind the study; details on the databases used and methodology; full results; and a discussion of implications and limitations of the study. Additional background and motivation Rates of firearm deaths and injuries in the United States substantially exceed those in other developed nations. 1,2 In 2014, 33,594 firearm deaths occurred in the U.S., of which 11,008 (32.8%) were homicides. 3 In that same year, 65,106 intentional, non-fatal firearm injuries occurred, implying a crude rate of 20.4 per 100, In addition to high rates of fatal and non-fatal firearm injuries related to crime, 461 unintentional firearm deaths occurred in the U.S. in 2014, as well as 15,928 unintentional, non-fatal injuries (5.4 per 100,000). 5,6 These included 1,960 unintentional injuries involving children aged <18 years. 5 Despite high rates of unintentional firearm injuries, many studies demonstrating that the availability of firearms is a risk factor for unintentional firearm injuries, 7-11 and recognition by the National Rifle Association (NRA) that firearm safety and education is critical for those operating firearms, 12 there remains active public debate about the safety of firearm use. Indeed, although it is recognized that care should be taken when using firearms, it is often contended that injuries primarily occur in the hands of inexperienced users and that experience and training alone can eliminate or markedly reduce firearm safety concerns. The purpose and motivation of this study was to investigate this possibility using a unique natural experiment, the NRA annual meeting. We hypothesized that firearm users who attend these meetings would be less likely to use firearms during the period of meeting attendance compared to identical days in the weeks before or after these meetings and that, as a result, population rates of firearm injuries might decline due to the brief period of firearm abstinence even among presumably avid, skilled users. We hypothesized that such a relationship could be plausibly identified in large, national data given that attendance at NRA meetings is substantial approximately 81,000 NRA members attended the 2017 annual meeting held in Atlanta, GA 13 and that individuals travel from across the U.S. to attend these meetings for example, 60% of those attending the 2017 meeting traveled from >200 miles away and approximately 27% traveled from >500 miles away. 13 2

4 Additional information on databases and methods Data sources Our primary analysis identified firearm injuries during dates of NRA annual conventions using the Truven Health Analytics MarketScan Commercial Claims database covering the period This database provides information on health care utilization for patients aged <65 years enrolled in private insurance plans through a participating employer, health plan, or government organization. Compared to the general U.S. population, the Marketscan population is slightly more female, more likely to live in the southern U.S., and less likely to live in the western U.S. 14 We defined a firearm injury as either an emergency department visit or hospitalization for firearm injury, identified according to International Classification of Disease, Ninth Edition (ICD-9) injury diagnosis codes E922.X, E955.X, E965.X, E970.X, E985.X, or E Although the commercially insured population is not reflective of the general U.S. population, which includes uninsured and those receiving public insurance, we required health care utilization data with exact dates of service to identify firearm-related health care utilization on the dates of NRA annual meetings and surrounding control dates. Other administrative databases, such as the Healthcare Cost and Utilization Project (HCUP) inpatient and emergency department databases, 16 include firearm injuries for a broader population of individuals requiring hospital care but do not provide exact dates of service. Moreover, in a previous analysis of HCUP data, those with private insurance accounted for nearly a third of emergency department visits for unintentional firearm injury, making this an important population to consider. 15 Study sample and outcome measures Calendar dates and locations of NRA annual conventions were obtained for each year during 2007 to 2015 (Table S1). We identified all individuals in the Marketscan database who received any medical care on NRA meeting dates (as determined by inpatient or outpatient medical claims for care provided on those dates), as well as all individuals who received care during identical days in the 3 weeks before and after convention dates (control group). For example, for the 2015 NRA annual convention held Friday, April 10 to Sunday, April 12 in Nashville, TN, the treatment group consisted of individuals who received outpatient (including emergency department) or inpatient care during those dates and the control group consisted of all individuals who received care Friday through Sunday in the 3 weeks before and after the convention. The primary outcome was the proportion of individuals who received care for a firearm injury during NRA annual meeting dates and control dates, identified according to ICD-9 injury diagnosis codes listed above. Analysis 3

5 We first plotted the unadjusted proportion of beneficiaries with a firearm-related injury during NRA meeting dates and for each of 6 control periods in the surrounding 3 weeks. We then conducted an event-study analysis in which a beneficiary-level multivariable linear regression was estimated of firearm-related injury (binary variable equal to 1 if a beneficiary had a claim for firearm-related injury) as a function of whether a beneficiary received care during an NRA convention date or one of 6 surrounding control dates (indicator variables were included for NRA convention and control dates), week of year and day of week fixed effects (to control for seasonal trends in firearm injuries that could be correlated with NRA convention dates), state fixed effects (thereby estimating injury rates on NRA vs control dates within the same state), patient age (<25 years, 25-34, 35-44, 45-54, 55-64, and >65), and patient sex. Linear models were estimated due to failure of the maximum likelihood algorithm to converge for logistic models. Robust standard errors were clustered at the state-level. We plotted adjusted firearm injury rates for NRA convention dates and each set of control dates, using the marginal standardization form of predictive margins averaged over the distribution of covariates in our sample. 17 We also reported the adjusted proportion of individuals receiving care for a firearm injury on NRA meeting dates versus all control dates combined, In pre-specified subgroup analyses, we stratified this regression according to census region and state-level tercile of gun ownership rates, 18 hypothesizing that changes in firearm-related injury rates during NRA meeting dates would be largest in areas with highest firearm use; according to patient sex, hypothesizing that changes in firearmrelated injury rates during meeting dates would be largest among males, who in the 2017 NRA annual meeting accounted for 85% of attendees 13 ; and according to whether the NRA convention was held in a given beneficiary s state in a given year, hypothesizing that any reductions in firearm injuries during NRA convention dates would be largest when the NRA convention was hosted in a city closer to a given beneficiary s home, making it easier to attend. For example, in the 2017 NRA meeting, 40% of attendees traveled from <200 miles away. 13 A formal test of interactions was conducted for all subgroup analyses. Analyses were performed in Stata (v. 14). The 95% confidence interval around reported estimates reflects in each tail or p This study was approved by the institutional review board at Harvard Medical School. Additional analyses We assessed the sensitivity of our findings to a broader definition of control periods for NRA meeting dates, using the identical days in the 4 weeks before and after annual meeting dates. Additionally, many of the firearm injuries observed in the commercially insured patient population may reflect non-crime-related firearm injuries. We therefore also examined whether changes in rates of crimes involving a firearm were present during NRA annual meeting dates versus surrounding control periods, using the National Incident-Based Reporting System (NIBRS) crime-level dataset covering The database 4

6 includes information on crime incidents occurring in law enforcement agencies that report to NIBRS (currently, approximately one-third of U.S. law enforcement agencies report to NIBRS, capturing approximately one-third of all crimes). 19 In this secondary analysis, we identified all crimes in the NIBRS database that occurred on NRA meeting dates, as well as all crimes that occurred during identical days in the 3 weeks before and after meeting dates (control group). The main outcome for this analysis was the proportion of crimes involving a firearm on NRA meeting dates and control dates. We plotted the proportion of crimes involving a firearm during NRA annual meeting dates and for each of 6 control periods in the surrounding 3 weeks. We then estimated a crime-level multivariable linear regression of firearm-related crime (binary variable equal to 1 if a crime involved a firearm) as a function of whether a crime occurred on an NRA meeting date (binary variable equal to 1 if a crime occurred on an NRA meeting date and zero otherwise). Additional covariates included age (<22 years, 22-30, 31-40, 41-50, and >50), sex, and race of victim and offender, as well as state fixed-effects. Robust standard errors were clustered at the state-level. We reported the adjusted proportion of crimes involving a firearm on NRA meeting dates versus the control period. 5

7 Additional results Information on study population Overall, 75,567,650 unique beneficiary-period observations were included from 2007 to 2015, of which 10,883,433 (14.3%) occurred on a NRA annual meeting date. Given that NRA annual meeting dates were compared to 6 surrounding control periods (±3 weeks surrounding meeting dates), the observed proportion of total beneficiary observations occurring on NRA meeting dates is consistent with an equal likelihood of individuals seeking medical care during NRA meeting dates versus control periods (1/7th, or 14.3%, of all observations would be expected to occur during NRA convention dates). The mean patient age was 38.1, and the study population was 59.0% female (Table S2). Approximately half of the population resided in states in the lowest gun ownership rate tercile while 15% resided in states in the highest tercile, which is explained by the fact that states with relatively lower firearm-ownership rates tend to be heavily populated (such as New York, Massachusetts, and California). Overall, 2.9% (2,261,262/75,567,650) of enrollee-period observations occurred in a state hosting a NRA annual meeting in a given year. Additional findings Figure S1 presents unadjusted injury rates by week. In pre-specified subgroup analyses, the reduction in firearm injuries during NRA meeting dates was concentrated among men (2.3 per 100,000 men on meeting dates versus 3.1 per 100,000 men on control dates, p=0.008) with no corresponding difference in women (Table S3). Similarly, significant reductions in firearm injuries during NRA meeting dates were identified in the South (0.9 versus 1.5 per 100,000 individuals, p=0.007) and West (1.4 versus 1.6 per 100,000 individuals, p=0.034). Absolute reductions in firearm injuries during NRA meeting dates were largest in states ranking in the highest tercile of gun ownership rates (1.8 per 100,000 on meeting dates versus 2.5 per 100,000 on control dates, p=0.043), compared to differences in states in the bottom tercile (1.0 per 100,000 on both meeting and non-meeting dates, p=0.554). Reductions in firearm injuries during NRA meetings dates were larger when individuals resided in the state hosting the annual meeting in a given year (0.7 per 100,000 on meeting dates versus 1.9 per 100,000 on control dates, p<0.001) Overall and sub-group findings were similar when using a ±4 week control period (Table S4). Characteristics of crimes in the NIBRS analysis are reported in Table S5. There was no significant difference in the proportion of crimes involving a firearm on NRA annual meeting dates versus control dates (Figure S2). On meeting dates, 2.94% of all crimes involved a firearm, compared to 3.00% on control dates (p=0.32). Similar findings were observed after adjustment for demographics of both victim and offender and state fixed- 6

8 effects (2.96% of all crimes involved a firearm on NRA annual meeting dates versus 3.00% on control dates, adjusted, p=0.50). 7

9 Additional discussion and limitations of findings Summary We found lower rates of firearm injuries in a commercially insured population during calendar dates of NRA annual meetings compared to identical days of the week in the 3 weeks before and after these meetings. Reductions in firearm injuries during NRA annual meeting dates were present only among males and were largest in areas with higher rates of gun ownership. The reduction in firearm injury rates during NRA annual meeting dates was larger when individuals resided in the same state where the annual meeting was held in a given year. No changes were observed during NRA meeting dates in the proportion of crimes involving a firearm. These findings are consistent with a reduction in firearm injuries due to lower overall firearm use during the brief period when many gun owners may be attending the annual convention itself. Interpretation of findings and implications Many opponents of gun control reform contend that injuries related to firearms occur in the hands of unskilled users and that while care should be taken when using a firearm, firearms themselves are not inherently unsafe when used by those with experience. If correct, we hypothesized that firearm injury rates should remain stable during calendar dates of NRA annual meetings, a brief period when large numbers of avid gun owners are systematically disproportionately less likely to be using firearms due to the incapacitation effect of meeting attendance. If causal, the findings of this study highlight that firearm safety issues are relevant even among avid, experienced gun owners who may be more likely to attend NRA meetings. Although we observed small absolute reductions in firearm injury rates during dates of NRA annual meetings (1.19 vs 1.49 per 100,000), these reductions were large in relative terms (20.1% reduction). Absolute risk reductions of this magnitude have been demonstrated in studies of the relationship between firearm laws and firearm-associated fatalities Moreover, the overall rate of firearm injury observed in our study s commercially insured population is broadly consistent with national estimates reported by the Centers for Disease Control and Prevention in 2014 (crude rate 5.4 per 100,000), 6 once differences in firearm injury rates between insured and uninsured populations are accounted for. 15 Our study was observational and therefore we cannot conclude that reductions in population-level firearm injuries observed during dates of NRA annual meetings were directly due to reductions in overall firearm use by gun owners during these meetings. Several factors support this hypothesis, however. First, NRA annual meetings are large and attract attendees from across the U.S., making it plausible that such an effect might be identifiable in large, national data. In 2017, for instance, 81,000 NRA members attended the NRA annual meeting, with 60% of those attending traveling from more than 200 miles away. 13 Importantly, reductions in firearm injuries during NRA annual meeting dates need not necessarily stem from gun owners themselves attending NRA conventions. 8

10 For instance, if some venues of firearm use (e.g., ranges or hunting grounds) are closed during dates of NRA annual meetings, reductions in overall firearm injuries during meeting dates could also be observed. Similarly, if individuals are more likely to engage in recreational firearm use in groups, then the absence of some group members due to NRA meeting attendance may reduce the likelihood of remaining group members to use firearms during the dates of NRA meetings. Second, we accounted for seasonal factors that might spuriously lead to lower firearm injury rates on the specific dates of NRA annual meetings. Third, reductions in firearm injuries during dates of NRA annual meetings were only observed among men, which would be expected given that men account for nearly 85% of meeting attendees. 13 Fourth, reductions in firearm injuries during dates of NRA annual meetings were largest in areas where gun ownership is highest. If attendees of NRA annual meetings disproportionately live in areas with high gun ownership, we would expect reductions in firearm injuries during dates of NRA annual meetings to be largest in these areas if meeting attendance leads to a transient reduction in firearm use locally. Fifth, we demonstrated that overall reductions in firearm injury rates during NRA annual meeting dates were larger for individuals residing in the same state where the annual convention was held in a given year. If individuals are more likely to attend NRA annual meetings when meetings are closer to home, we would expect larger reductions in firearm injuries during dates of meetings that occur locally. Sixth, an implication of our findings is that even among experienced gun owners who might be more likely to attend NRA annual conventions the rate of firearm injury directly relates to the amount of firearm use. This is consistent with prior evidence that firearm training is inconsistently received by firearm owners and that the length of firearm training or how recently it was conducted bears little relationship with firearm storage practices, one measure of firearm safety. 23 Limitations Our study has several limitations. First, the study was observational and therefore the reductions in firearm injuries that were observed during dates of NRA annual meetings cannot be causally attributed to the meetings themselves, despite the robustness analyses that were performed. Second, it was possible to observe small, absolute reductions in firearm injuries during NRA meeting dates due to the large size of our data. This raises the concern of identifying statistically significant associations that are not clinically meaningful. However, the observed reductions were large in relative terms and broadly consistent with the magnitude of changes demonstrated in studies of the association between firearm-related injuries and firearm laws Third, our analysis of firearm injuries focused on the commercially insured population, rather than the uninsured, those with public insurance, or those with different private insurance. Overall rates of firearm injury, and the reduction observed in firearm injuries during dates of NRA annual meetings, may be different in these populations. Nonetheless, those with private insurance account for nearly a third of emergency department visits for unintentional firearm injury, making this an important population to consider. 15 We focused on the commercially insured population because exact dates of health care service utilization were required for our analysis. Although state Medicaid claims databases contain this information, these data were not available to us. Exact dates of service are also typically 9

11 unavailable in national hospital or emergency department discharge databases such as the Healthcare Cost and Utilization Project (HCUP). 16 Fourth, our analysis was limited to individuals aged <65 years. If firearm use and safety remains constant after this age, we would expect similar reductions in firearm injuries during NRA annual convention dates in this population (holding the likelihood of convention attendance constant). However, if firearm use increases after retirement or if firearm safety declines with age (perhaps due to age-related decline), larger reductions in firearm injuries during NRA annual convention dates may be expected in the >65 year old population. REFERENCES 1. Marczak L, O'Rourke K, Shepard D, Leach-Kemon K. Firearm Deaths in the United States and Globally, Jama 2016;316: Richardson EG, Hemenway D. Homicide, suicide, and unintentional firearm fatality: comparing the United States with other high-income countries, The Journal of trauma 2011;70: National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. National Center for Health Statistics Vital Statistics System for Numbers of Deaths. Firearm Deaths and Rates per 100,000. (Accessed 2017, August 15, at 4. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. National Electronic Injury Surveillance System. Violence-Related Firearm Gunshot Nonfatal Injuries and Rates per 100,000. (Accessed 2017, August 15, at 5. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. National Center for Health Statistics Vital Statistics System for Numbers of Deaths. Unintentional Firearm Deaths and Rates per 100,000. (Accessed 2017, August 15, at 6. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. National Electronic Injury Surveillance System. Unintentional Firearm Gunshot Nonfatal Injuries and Rates per 100,000. (Accessed 2017, August 15, at 7. Grossman DC, Mueller BA, Riedy C, et al. Gun storage practices and risk of youth suicide and unintentional firearm injuries. Jama 2005;293: Parker DJ, Sklar DP, Tandberg D, Hauswald M, Zumwalt RE. Fire fatalities among New Mexico children. Annals of emergency medicine 1993;22: Wintemute GJ, Teret SP, Kraus JF, Wright MA, Bradfield G. When children shoot children. 88 unintended deaths in California. Jama 1987;257: Cummings P, Grossman DC, Rivara FP, Koepsell TD. State gun safe storage laws and child mortality due to firearms. Jama 1997;278: Kellermann AL, Somes G, Rivara FP, Lee RK, Banton JG. Injuries and deaths due to firearms in the home. The Journal of trauma 1998;45: National Rifle Association. NRA Gun Safety Rules. (Accessed 2017, August 16, at 10

12 13. National Rifle Association Annual Meetings Attendee Survey Results (Accessed August 7, 2017, at Aizcorbe A, Liebman E, Pack S, Cutler DM, Chernew ME, Rosen AB. Measuring health care costs of individuals with employer-sponsored health insurance in the U.S.: A comparison of survey and claims data. Stat J IAOS 2012;28: Cuellar A, Stranges E, Stocks C. Hospital Visits in the U.S. for Firearm-Related Injuries, HCUP Statistical Brief #136. June Healthcare Cost and Utilization Project. (Accessed August 3, 2017, at Williams R. Using the margins command to estimate and interpret adjusted predictions and marginal effects. Stata Journal 2012;12: Kalesan B, Villarreal MD, Keyes KM, Galea S. Gun ownership and social gun culture. Inj Prev 2016;22: National Incident Based Reporting System (NIBRS). NIBRS Overview. (Accessed August 3, 2017, at Fleegler EW, Lee LK, Monuteaux MC, Hemenway D, Mannix R. Firearm legislation and firearm-related fatalities in the United States. JAMA Intern Med 2013;173: Humphreys DK, Gasparrini A, Wiebe DJ. Evaluating the Impact of Florida's "Stand Your Ground" Self-defense Law on Homicide and Suicide by Firearm: An Interrupted Time Series Study. JAMA Intern Med 2017;177: Chapman S, Alpers P, Jones M. Association Between Gun Law Reforms and Intentional Firearm Deaths in Australia, Jama 2016;316: Hemenway D, Solnick SJ, Azrael DR. Firearm training and storage. Jama 1995;273:

13 Table S1 NRA Annual Meetings Dates and Locations Location Dates Nashville, TN April 10-12, 2015 Indianapolis, IN April 25-27, 2014 Houston, TX May 3-5, 2013 St. Louis, MO April 12-15, 2012 Pittsburgh, PA April 29 - May 1, 2011 Charlotte, NC May 14-16, 2010 Phoenix, AZ May 15-17, 2009 Louisville, KY May 16-18, 2008 St. Louis, MO April 13-15,

14 Gender Table S2 Characteristics of the study population No. of beneficiary-period observations Percent of total Male 31,017, Female 44,549, Age <25 years 19,190, years 9,150, years 12,644, years 17,024, years 17,557, U.S. Census Region of Residence Northeast 15,489, Midwest 18,255, South 28,176, West 13,646, State Gun Ownership Rate in Terciles First (lowest) 35,558, Second 28,917, Third (highest) 11,091, Convention held in state in given year No 73,306, Yes 2,261,

15 Table S3 Subgroup analyses of firearm injuries during NRA annual convention dates and control dates Control dates No. observations NRA annual meeting dates No. observations Control dates Firearm injury rates (per 100,000) NRA annual meeting dates Firearm injury rates (per 100,000) Adjusted Difference (95% CI) P-value Overall 64,684,217 10,883, (-0.5, -0.1) N/A Gender Male 26,555,918 4,462, (-1.3, -0.2) Female 38,128,299 6,421, (-0.2, 0.2) U.S. Census Region Northeast 13,247,971 2,241, (-0.6, 0.3) Midwest 15,629,393 2,626, (-0.4, 0.2) South 24,101,796 4,074, (-0.9, -0.2) West 11,705,057 1,941, (-0.5, 0.0) State Gun Ownership Tercile First (lowest) 30,453,156 5,105, (-0.3, 0.2) Second 24,738,446 4,179, (-0.7, -0.1) Third (highest) 9,492,615 1,598, (-1.3, 0.0) In-State Convention No 62,751,874 10,554, (-0.5, -0.1) Yes 1,932, , (-1.9, -0.5) <0.001 P-value for interaction

16 Table S4 Subgroup analyses of firearm injuries during NRA annual convention dates and control dates using a ±4 week control period Control dates No. observations NRA annual meeting dates No. observations Control dates Firearm injury rates (per 100,000) NRA annual meeting dates Firearm injury rates (per 100,000) Adjusted Difference (95% CI) P-value Overall 86,417,118 10,883, (-0.06, -0.7) N/A Gender Male 35,479,596 4,462, (-1.4, -0.1) Female 50,937,520 6,421, (-0.4, 0.2) Age <25 years 21,964,350 2,748, (-1.3, 0.1) years 10,448,723 1,325, (-1.3, 0.3) years 14,450,934 1,825, (-0.8, 0.4) years 19,468,944 2,453, (-0.7, -0.1) years 20,084,168 2,530, (-0.5, 0.2) U.S. Census Region Northeast 17,687,166 2,241, (-0.8, 0.3) Midwest 20,884,546 2,626, (-0.6, 0.1) South 32,200,992 4,074, (-1.0, -0.1) West 15,644,415 1,941, (-0.7, 0.0) State Gun Ownership Tercile First (lowest) 40,659,472 5,105, (-0.5, 0.2) Second 33,042,704 4,179, (-0.9, -0.1) Third (highest) 12,714,941 1,598, (-1.2, -0.1) In-State Convention No 83,832,784 10,554, (-0.7, 0.0) Yes 2,584, , (-1.7, -0.7) <0.001 P-value for interaction

17 Table S5 Characteristics of victims and offenders in National Incident-Based Reporting System (NIBRS) Age Victim Crimes Percent of total (%) <22 years 183, years 209, years 164, years 134, >50 years 125, Gender Male 474, Female 341, Race White 584, Black 220, Other 11, Age Offender <22 years 225, years 246, years 171, years 113, Gender >50 years 59, Male 609, Female 207, Race White 524, Black 279, Other 12,

18 Figure S1 Unadjusted firearm injuries among commercially insured individuals on dates of NRA annual meetings and control dates during

19 Figure S2 Adjusted proportion of crimes involving a firearm on dates of NRA annual conventions and control dates during