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Firearm Ownership and Suicide Rates Among US Men and Women, 1981–2013 Michael Siegel, MD, MPH, and Emily F. Rothman, ScD, MS Objectives. To examine the relationship between state-level firearm ownership rates and gender-specific, age-adjusted firearm and total suicide rates across all 50 US states from 1981 to 2013. Methods. We used panel data for all 50 states that included annual overall and gender-specific suicide and firearm suicide rates and a proxy for state-level household firearm ownership. We analyzed data by using linear regression and generalized estimating equations to account for clustering. Results. State-level firearm ownership was associated with an increase in both male and female firearm-related suicide rates and with a decrease in nonfirearm-related suicide rates. Higher gun ownership was associated with higher suicide rates by any means among male, but not among female, persons. Conclusions. We found a strong relationship between state-level firearm ownership and firearm suicide rates among both genders, and a relationship between firearm ownership and suicides by any means among male, but not female, individuals. Policy implications. For male persons, policies that reduce firearm ownership will likely reduce suicides by all means and by firearms. For female persons, such policies will likely reduce suicides by firearms. (Am J Public Health. 2016;106:1316–1322. doi:10.2105/ AJPH.2016.303182)
A
pproximately 40 000 people die as a result of suicide each year in the United States, making it the 10th leading cause of death in the nation and costing approximately $44 billion per year.1,2 Although firearm homicide may be the most frequently reported aspect of firearm mortality by the press, the number of annual firearm suicides is almost twice as high as the number of firearm homicides. In 2013, there were 11 208 firearm homicides and 21 175 firearm suicides.1 Two recent studies demonstrated a strong association between levels of firearm ownership and rates of firearm homicide at the state level.3,4 We examined the relationship between state-level firearm ownership and state-specific suicide rates. Two major lines of research have explored the relationship between firearm prevalence and suicide rates.5–7 A number of individual-level studies have demonstrated that the presence of a firearm in the home increases the risk of suicide, both for the firearm owner and for household members.5
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However, these studies are limited because they only examine the individual risks of firearm ownership. They cannot be used to assess whether the prevalence of firearm ownership in the population affects suicide rates for an expanded geographical area. Moreover, the previous line of research has been criticized because of the possibility that people who live in households with firearms are inherently more likely to attempt suicide and that persons in a home in which a suicide has occurred may be more likely to recall firearm ownership.8,9 A second, complementary line of research addresses these limitations through crosssectional studies that correlate levels of firearm
ownership with rates of firearm suicide at the state or regional level. These studies have consistently found a relationship between increased levels of firearm ownership in a state or region and higher rates of firearm suicide.9–25 However, the results regarding the association between firearm ownership in a state or region and total suicide rates have been mixed, with several studies failing to find a relationship.15–17,26–29 This conflicting evidence led the National Research Council in 2004 to conclude that this association is more modest than the association between [individual] firearm ownership and firearm suicide; it is less consistently observed across time, place, and persons; and the causal relation remains unclear.8(p192)
Since the National Research Council report in 2004, 4 additional ecological studies have reported a significant association between higher levels of firearm ownership and overall suicide rates at the regional10 or state7,9,11 level. Still, 2 of these studies analyzed data for only a single year,7,9 limiting the generalizability of the findings. As recently as October 5, 2014, a Washington Post “fact checker” article reported that “studies have shown little connection between suicides and access to firearms.”30 In fact, most data used in the existing studies comprised only a cross-section in time; only 710,11,17,19,22,23,25 contained panel data over multiple years. Only 2 of the studies7,11 analyzed data subsequent to 2002, and none examined data more recent than 2009. Studies analyzing data over long time periods are valuable because they assess the
ABOUT THE AUTHORS
All of the authors are with the Department of Community Health Sciences, Boston University School of Public Health, Boston, MA. Correspondence should be sent to Michael Siegel, MD, MPH, Department of Community Health Sciences, Boston University School of Public Health, 801 Massachusetts Ave, 4th Floor, Boston, MA 02118 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This article was accepted March 2, 2016. doi: 10.2105/AJPH.2016.303182
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effects of variation in firearm availability not only between states but also within states over time. Recently, we advanced the field of firearms research by compiling a comprehensive database of state-level firearm ownership, firearm and total homicide rates, and 20 different sociodemographic control variables for the 30-year period from 1981 to 2010.3,4,31 Another important criticism of much of the existing literature on firearm ownership and suicide is that it has relied upon a proxy measure of state-level firearm ownership that correlates with survey measures of household firearm prevalence only at a level of 0.80.32 We recently developed an improved proxy measure for firearm ownership at the state level, which increases the correlation with surveymeasured household firearm prevalence from 0.80 to 0.95.32 This new proxy takes into account not only the proportion of suicides in which a firearm was used (a long-standing, validated measure of state-level firearm ownership), but also the state’s hunting license rate. A final limitation of the existing literature is that only 1 research group (5 studies) has examined the relationship between firearm ownership and firearm suicide rates separately by gender.7,9,10,24,25 The results are conflicting, with 1 study showing a stronger relationship for women,9 2 showing a stronger relationship for men,7,24 and 2 showing no difference.10,25 In this article, we expanded our existing database through 2013 and added data on gender-specific firearm and overall suicide rates by state for the entire period from 1981 to 2013. This study expands upon previous work by incorporating the most recent data, analyzing data over 3 decades, using a new and improved proxy for state-level firearm ownership, examining the relationship between firearm ownership levels and firearm suicide rates separately by gender, and controlling for the most extensive panel to date of annual, state-specific factors that could potentially confound the association between firearm ownership and suicide rates. We examined the relationship between firearm ownership and gender-specific, age-adjusted firearm and total suicide rates across all 50 states during the 33-year period 1981 through 2013, while controlling for region, urbanization, population density, proportion of Catholic adherents, per capita gross domestic product, per capita personal disposal income,
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household income, education, divorce rate, alcohol use, violent crime rate, nonviolent crime rate, and incarceration rate. To the best of our knowledge, this is the most comprehensive study to date, both in terms of the number of years in the analysis and the comprehensiveness of the control variables used.
METHODS For the 33-year period from 1981 to 2013, we assembled a panel of data for all 50 states that included annual overall and gender-specific suicide and firearm suicide rates and a proxy for state-level household firearm ownership. We investigated the relationship between the firearm ownership level in a state for a given year and the adjusted overall and firearm suicide rate in that state and year, with control for factors that could confound the association. We used a linear regression model, accounting for clustering of observations among years by entering fixed effects for each year. We accounted for clustering of observations among states by using a generalized estimating equations (GEE) approach. Our basic approach, including a detailed description of variables, data sources, and analytic methods, has been published previously.3
Variables and Data Sources The outcome variable was the ageadjusted, gender-specific overall, firearm, or nonfirearm suicide rate, obtained from the Centers for Disease Control and Prevention’s (CDC’s) Web-Based Injury Statistics Query and Reporting Systems database.1 As there were 33 years and 50 states, the total number of observations was 1650. However, we were limited by the small number of female firearm suicides in some states during some years. For the years 1999 to 2013, the CDC does not report data when the number of counts in a cell (e.g., female firearm suicides) is fewer than 10. Thus, we were missing data for 148 year–state observations, resulting in a final sample size of 1502 for the analyses of female suicide rates. The main predictor variable was the prevalence of household firearm ownership in a given state for a given year, measured by our new proxy variable.32 The use of a proxy is necessary because there are no state-level data
on firearm ownership for most of the study period. The Behavioral Risk Factor Surveillance System (BRFSS) has not collected state firearm ownership data since 2004.3 Previous studies have used a decent proxy: the percentage of suicides in which a firearm was used (firearm suicides divided by all suicides, or FS/S). However, the measure used in those previous studies correlates with survey measures of firearm ownership only at a level of 0.80.32 Our new proxy variable, which includes a state’s hunting license rate in addition to FS/S, improves this correlation to 0.95.32 The details of how our new proxy variable was validated are available here.32 The major problem with the traditional proxy is that it tends to overestimate household gun ownership in states with low hunting license rates and to underestimate household gun ownership in states with high hunting license rates. The correlation between hunting license rates and survey measures of state household gun ownership is 0.80. By accounting for hunting licenses, the new proxy produces more accurate estimates. For example, in Hawaii, the state with the lowest hunting license rate, the BRFSS gun prevalence estimate for 2001 is 9%, the old proxy is 23%, and the new proxy is 10%. In South Dakota, the state with the highest hunting license rate, the BRFSS gun prevalence estimate for 2001 is 57%, the old proxy is 41%, and the new proxy is 53%. We controlled for the following state-level factors, which could potentially be related both to firearm ownership and suicide rates: level of urbanization, educational attainment, unemployment, median household income, per capita alcohol consumption, nonhomicide violent crime rate (aggravated assault, robbery, and forcible rape), nonviolent (property) crime rate (burglary, larceny theft, and motor vehicle theft), incarceration rate, and divorce rate. To control for differences in suicide rates by region, we included indicator variables for the 4 US Census regions (Northeast, Midwest, South, and West). To further control for urban–rural differences, we included population density for each state, obtained from the US Census.33 To control for differences between states and over time in the state of the economy we included 2 measures: (1) the per capita gross domestic product, and (2) the per capita personal disposable income. These measures
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were obtained from the US Bureau of Economic Analysis.34 Finally, we controlled for the number of Catholic adherents per 1000 persons in each state by using data from the Association of Religion Data Archives35 for the years 1980, 1990, 2000, and 2010 and interpolating to derive estimates for the intervening years.
Model and Statistical Analysis Our outcome variable—age-adjusted suicide rates—was approximately normally distributed. Therefore, we used a linear regression model, which follows the approach used in several previous studies.7,11–13,24,27 Because our data were a panel with multiple observations each year (n = 50) and multiple years of state data (n = 33), there were 2 sources of clustering. To account for clustering by year, we included year as a fixed effect in the regression models. To account for clustering among states, we used a GEE approach with robust variance estimators. This follows the approach taken by Miller et al. to account for clustering by region.25 In the GEE models, we tested a variety of assumptions about the nature of the working correlation matrix. We chose the model with the best fit—a correlation matrix with an autoregressive structure—by selecting the model with the lowest quasilikelihood under the independence model criterion. We ran 2 models: (1) a full model that included all state-level variables, and (2) a parsimonious final model that only included variables significant according to a Wald test at a level of .05, produced with a backward stepwise regression procedure. To ease the interpretation of regression coefficients, we present the estimated changes in suicide rates associated with an increase of 10 percentage points in a state’s firearm ownership prevalence. We conducted all analyses with the GENMOD procedure in SAS version 9.3 (SAS Institute Inc, Cary, NC).
RESULTS Over the 33-year study period, the mean estimated percentage of firearm ownership ranged from a low of 12.2% in Hawaii to a high of 72.8% in Wyoming, with an average overall for all states of 41.0% (Table 1).
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TABLE 1—Mean Average Household Firearm Ownership Rate and Gender-Specific, Age-Adjusted Firearm-Related Suicide Rates, by State: United States, 1981–2013 Average Firearm Suicide Rate, 1981–2013 (per 100 000) State United States
Average Firearm Ownership, % (Rank)
Male (Rank)
Female (Rank)
41.0
14.2
2.1
Hawaii
12.2 (1)
4.8 (3)
0.5 (4)
Massachusetts
13.9 (2)
4.2 (1)
0.4 (3)
Rhode Island
15.5 (3)
5.2 (5)
0.6 (5)
New Jersey
16.9 (4)
4.5 (2)
0.4 (2)
Connecticut
21.6 (5)
6.4 (6)
0.7 (6)
New York
21.7 (6)
5.1 (4)
0.4 (1)
Illinois
25.0 (7)
7.8 (7)
0.9 (7)
California
26.6 (8)
10.7 (11)
1.6 (19)
Delaware
28.1 (9)
10.6 (10)
1.2 (13)
Maryland
30.9 (10)
9.9 (8)
1.1 (10)
Florida
32.3 (11)
14.2 (24)
2.6 (34)
Washington
34.0 (12)
13.6 (21)
2.0 (25)
Ohio
34.3 (13)
11.4 (13)
1.5 (18)
New Hampshire
35.1 (14)
12.1 (18)
1.7 (20)
Indiana
37.5 (15)
13.5 (20)
1.7 (21)
Iowa
37.7 (16)
11.3 (12)
1.1 (11)
Colorado
38.4 (17)
17.1 (38)
2.5 (32)
Pennsylvania
38.4 (18)
11.5 (14)
1.3 (15)
Nevada
38.8 (19)
24.4 (49)
4.2 (50)
Minnesota
39.1 (20)
10.2 (9)
0.9 (8)
Arizona
39.5 (21)
19.2 (44)
3.2 (47)
Michigan
39.6 (22)
11.7 (16)
1.3 (14)
New Mexico
40.5 (23)
20.8 (46)
3.0 (42)
Virginia
40.6 (24)
14.5 (26)
2.1 (27)
Texas
41.7 (25)
14.4 (25)
2.5 (33)
Kansas
41.8 (26)
14.1 (23)
1.8 (22)
Nebraska
42.1 (27)
11.8 (17)
1.4 (16)
North Carolina
42.5 (28)
15.1 (29)
2.4 (29)
Wisconsin
42.8 (29)
11.6 (15)
1.2 (12)
Oregon
43.4 (30)
16.9 (35)
2.5 (31)
Utah
43.5 (31)
17.4 (41)
2.2 (28)
Missouri
43.6 (32)
15.2 (30)
1.9 (24)
South Carolina
44.6 (33)
15.0 (27)
2.7 (37)
Georgia
44.8 (34)
16.0 (31)
2.8 (38)
Oklahoma
46.6 (35)
17.2 (39)
3.0 (41)
Kentucky
48.6 (36)
17.7 (42)
2.7 (35)
Louisiana
48.6 (37)
16.3 (32)
3.1 (44)
Maine
48.7 (38)
14.0 (22)
1.8 (23)
Continued
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TABLE 1—Continued Average Firearm Suicide Rate, 1981–2013 (per 100 000) State
Average Firearm Ownership, % (Rank)
Male (Rank)
Female (Rank)
Alabama
49.7 (39)
16.7 (34)
3.0 (43)
North Dakota
51.1 (40)
13.0 (19)
1.0 (9)
Tennessee
51.7 (41)
16.9 (37)
2.9 (40)
Vermont
53.2 (42)
16.9 (36)
2.1 (26)
Mississippi
53.7 (43)
16.4 (33)
3.1 (45)
Arkansas
55.1 (44)
17.4 (40)
2.9 (39)
Alaska
56.0 (45)
20.7 (45)
3.7 (48)
West Virginia
56.8 (46)
18.4 (43)
2.4 (30)
South Dakota
60.6 (47)
15.0 (28)
1.4 (17)
Idaho
61.6 (48)
21.0 (47)
2.7 (36)
Montana
68.4 (49)
23.5 (48)
3.2 (46)
Wyoming
72.8 (50)
26.1 (50)
3.9 (49)
Among the 50 states, the average percentage of firearm ownership decreased from 45.6% in 1981 to 36.5% in 2013 (P < .01). Over the study period, the mean ageadjusted firearm suicide rate among male individuals ranged from a low of 4.2 per 100 000 in Massachusetts to a high of 26.1 per 100 000 in Wyoming, with an average over all states of 14.2 per 100 000 (Table 1). The mean age-adjusted firearm suicide rate among female individuals over the study period ranged from a low of 0.40 per 100 000 in New York to a high of 4.2 per 100 000 in Nevada, with an average over all states of 2.1 per 100 000. Among the 50 states, the average male firearm suicide rate decreased slightly from 14.5 per 100 000 in 1981 to 13.9 per 100 000 in 2013, and the average female firearm suicide rate decreased slightly from 2.6 per 100 000 to 2.3 per 100 000. The average percentage of suicides in which a firearm was used was consistently 1.6 times higher among male (62.0% over study period) than among female persons (39.1% over study period; P < .01; data not shown). Among both genders, the average proportion of suicides in which a firearm was used decreased by approximately 12% to 15% over the course of the study period, from 65.5% during 1981 to 1990 to 57.8% during 2000 to 2013 among male individuals and from 41.5% to 35.3% among female individuals. All of these decreases were statistically significant at the P < .01 level.
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In bivariate analyses, there was a strong correlation between state-level firearm ownership and the adjusted firearm-related suicide rate for both genders, with firearm ownership explaining 71% of the variation (R2 = 0.71) in the firearm suicide rate for male individuals and 49% of the variation (R2 = 0.49) in the firearm suicide rate for female individuals (Figures 1 and 2). In a bivariate analysis (a GEE linear regression model with year fixed effects and accounting for clustering by state, but without any predictor variables besides firearm ownership), the firearm ownership proxy was a significant predictor of male firearm suicide rates (increase of 3.3 per 100 000 for each 10-percentage-point increase in firearm ownership), male nonfirearm suicide rates (decrease of 2.2 per 100 000 for each 10percentage-point increase in firearm ownership), and total suicide rates (increase of 1.6 per 100 000 for each 10-percentage-point increase in firearm ownership; Table 2). For female individuals, the firearm ownership proxy was a significant predictor of firearm suicide rates (increase of 0.5 per 100 000 for each 10-percentage-point increase in firearm ownership) and nonfirearm suicide rates (decrease of 0.4 per 100 000 for each 10-percentage-point increase in firearm ownership), but was not associated with total suicide rates.
In the full multivariate GEE linear regression models, the firearm ownership proxy was a significant predictor of male firearm suicide rates (increase of 3.1 per 100 000 for each 10-percentage-point increase in firearm ownership), male nonfirearm suicide rates (decrease of 1.5 per 100 000 for each 10percentage-point increase in firearm ownership), and total suicide rates (increase of 1.9 per 100 000 for each 10-percentage-point increase in firearm ownership; Table 2). For female persons, the firearm ownership proxy was a significant predictor of firearm suicide rates (increase of 0.4 per 100 000 for each 10-percentage-point increase in firearm ownership) and nonfirearm suicide rates (decrease of 0.5 per 100 000 for each 10percentage-point increase in firearm ownership), but was not associated with total suicide rates. The same pattern emerged in the final models. To examine whether our use of a proxy for household firearm ownership explains the observed findings, we repeated the analyses in 2 ways: (1) using the traditional FS/S proxy, and (2) restricting the analysis to the years 2001, 2002, and 2004 and using BRFSS survey data on household firearm ownership. The positive relationship between gun ownership and the overall male suicide rate remained significant when we used the FS/S proxy (increase of 1.0 per 100 000 for each 10 percentage point increase in gun ownership) and when we used only survey data (increase of 1.7 per 100 000 for each 10-percentagepoint increase in gun ownership). The positive relationship between gun ownership and female firearm suicide rates also remained significant when we used the FS/S proxy (increase of 0.6 per 100 000 for each 10percentage-point increase in gun ownership) and when using only survey data (increase of 0.5 per 100 000 for each 10-percentage-point increase in gun ownership). In the final models, other covariates that consistently predicted higher suicide rates were West region, higher alcohol consumption, higher divorce rate, higher violent crime rate, lower population density, and lower per capita gross domestic product. Each of these variables was also significantly related to the main predictor variable (gun ownership).
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Adjusted FS Rate/100 000
30.0
25.0
20.0
15.0
10.0
5.0
0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Average Gun Ownership, % Note. FS = firearm suicide; y = 0.3209x + 1.022; R2 = 0.71.
FIGURE 1—Relationship Between Average State-Level Gun Ownership and Average Male Age-Adjusted Firearm Suicide Rate: United States, 1981–2013
firearm ownership in a state and higher firearm suicide rates for both genders. Among male individuals, we also found a significant association between higher firearm ownership and higher overall suicide rates, but this relationship did not hold for female individuals.
DISCUSSION To the best of our knowledge, this is the most comprehensive analysis of the relationship between firearm ownership and gender-specific suicide rates among the 50 US states. We found a strong relationship between higher levels of 4.5
Adjusted FS Rate/100 000
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Average Gun Ownership, % Note. FS = firearm suicide; y = 0.0517x – 0.0923; R2 = 0.49.
FIGURE 2—Relationship Between Average State-Level Gun Ownership and Average Female Age-Adjusted Firearm Suicide Rate: United States, 1981–2013
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Our study adds to the consistent finding that, among both genders, increased prevalence of firearms is associated with an increase in the firearm-specific suicide rate. The magnitude of this relationship is substantial. Based on our model, if the firearm ownership in Wyoming were 41.0% (the average for all states) instead of 72.8%, its male firearm suicide rate would be lower by 9.9 per 100 000 (a 38% decline), and its female firearm suicide rate would be lower by 2.2 per 100 000 (a 56% decline). Our findings also add to the evidence that higher gun ownership is associated with higher overall suicide rates among male persons. Based on our model, if gun ownership in Wyoming were at the average for all states (41.0%) instead of at 72.8%, the overall male suicide rate in Wyoming would be lower by 5.7 per 100 000 among male persons (a 16% decline). Unlike a number of previous studies,7,9,10,24,25 we did not find a relationship between gun ownership and overall suicide rates among female persons. Because of these conflicting results, this issue warrants further study. Some have questioned whether the association between firearm ownership and homicide deaths might be the result of a so-called “reverse association”—that is, because there are many homicides in an area, more people will obtain firearms to protect themselves from that threat. A strength of this study is that, unlike previous studies on the relationship between firearm ownership and homicide rates at the state level, the observed association between firearm ownership and suicide rates is unlikely to be attributable to a reverse association. Although it is plausible that people might acquire more firearms if there are more homicides occurring near them, it does not seem likely that people are responding to increased suicide rates in their area by going out to purchase more firearms for themselves. As Briggs and Tabarrok have argued, the only plausible source of reverse association is that an individual may purchase a gun specifically because of suicidal intent.11 However, this would have almost no effect on gun ownership levels.11 Thus, we believe that the observed association between increased firearm ownership and higher firearm suicide is a causal one.
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TABLE 2—Change in Firearm, Nonfirearm, and Total Age-Adjusted Suicide Rates (per 100 000 Population) Associated With a 10-Percentage-Point Increase in State-Level Firearm Ownership Rate—by Gender Unadjusted Modela (95% CI)
Adjusted Modelb (95% CI)
Final Modelc (95% CI)
Overall
+1.6* (+1.3, +2.0)
+1.9* (+1.3, +2.5)
+1.9* (+1.5, +2.4)
Firearm Nonfirearm
+3.3* (+3.0, +3.5) –2.2* (–2.5, –1.9)
+3.1* (+2.7, +3.5) –1.5* (–1.8, –1.2)
+3.1* (+2.7, +3.5) –1.6* (–1.9, –1.3)
Outcome Variable Male suicide rate
Female suicide rate Overall
+0.0 (–0.2, +0.3)
–0.0 (–0.2, +0.2)
–0.0 (–0.2, +0.2)
Firearm
+0.5* (+0.4, +0.6)
+0.4* (+0.3, +0.5)
+0.4* (+0.3, +0.5)
Nonfirearm
–0.4* (–0.6, –0.2)
–0.5* (–0.6, –0.3)
–0.4* (–0.6, –0.3)
Note. CI = confidence interval. The values in the table represent the estimated change in the specified suicide rate for each 10-percentage-point increase in the predictor variable. For example, a value of +1.6 indicates that there is an increase of 1.6 per 100 000 in the suicide rate for each 10-percentage-point increase in household firearm ownership (e.g., comparing a state with 30% firearm ownership rate to a state with 40% firearm ownership rate would indicate a suicide rate difference of 1.6 per 100 000). a Based on a generalized estimating equation linear regression model with year fixed effects and accounting for clustering by state, but without any predictor variables besides firearm ownership. b Controlled for region, level of urbanization, population density, educational attainment, unemployment, median household income, per capita alcohol consumption, proportion of Catholic adherents, nonhomicide violent crime rate (aggravated assault, robbery, and forcible rape), nonviolent (property) crime rate (burglary, larceny theft, and motor vehicle theft), incarceration rate, divorce rate, per capita gross domestic product, and per capita disposable personal income. c Parsimonious model including only variables significant at the P < .05 level. *P < .05.
confounder that would still be influential over and above what is already included in the models. Nevertheless, repeating this study with a longitudinal design would help to establish whether the observed relationship is a causal one.
Public Health Implications The public health implication of these findings is that reductions in the prevalence of firearms may be an effective strategy for reducing overall and firearm-related suicides among male persons and for reducing firearm-related suicides among female persons. As suicide is the 10th leading cause of death in the United States, and firearmrelated deaths and injuries are extraordinarily costly, reducing firearm-related selfinjury and suicide is a public health imperative. CONTRIBUTORS M. Siegel conceptualized the study, collected the data, and led the data analysis and writing. E. F. Rothman assisted with the study design, analytical plan, writing, and revisions.
HUMAN PARTICIPANT PROTECTION
There are at least 2 potential explanations for our observation of an increased suicide rate by any method among male persons in association with higher state-level firearm ownership prevalence. First, it may be that at least some suicides are impulsive and that the ease with which a person can obtain a highly lethal means of suicide (i.e., a firearm), the more suicides will be completed.6,25 The impulse to attempt suicide may wane relatively quickly, such that the lack of ease in finding a lethal means may allow enough time to pass so that the suicidal impulse subsides or intervention occurs.6,11 Second, as Miller et al. argue, overall suicide rates may be lowered by “reducing population-level access to lethal means.”6(p401) Several natural experiments have demonstrated that overall suicide rates may be reduced by eliminating lethal means, such as removing carbon monoxide from gas used in ovens and heaters in the United Kingdom, banning toxic pesticides in Sri Lanka, and reducing soldiers’ access to firearms on weekends in Israel.6 One possible explanation for why we failed to find an association between higher levels of gun ownership and higher overall suicide rates among female individuals is that women tend
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to be less impulsive than men, so the reduced availability of lethal means might not prevent suicide as the suicidal ideation is more stable. In contrast, men who have high impulsivity but do not have easy access to a lethal means might be more likely to experience a prompt resolution of their impulsive suicidal ideation such that the lack of a lethal means actually prevents suicide altogether.
Limitations There are several limitations of this study. First, we used a proxy measure of firearm ownership rather than self-report, survey-based measures. However, we used a well-established proxy variable that has a correlation of 0.95 with survey-measured gun ownership. To remedy this problem, the CDC should reinstate self-reported firearm ownership prevalence surveillance through its BRFSS survey. A second limitation is that this is a crosssectional study, so an unknown confounder may explain the observed relationship. However, because of the number and scope of predictor variables we included in our analysis, it is difficult to imagine a potential
Institutional review board approval was not needed for this study because secondary data sources were used.
REFERENCES 1. Centers for Disease Control and Prevention. WebBased Injury Statistics Query and Reporting Systems: fatal injury reports. Available at: http://www.cdc.gov/injury/ wisqars/fatal_injury_reports.html. Accessed August 7, 2015. 2. Heron M. Deaths: leading causes for 2011. Natl Vital Stat Rep. 2015;64(7):1–96. 3. Siegel M, Ross CS, King C. The relationship between gun ownership and firearm homicide rates in the United States, 1981–2010. Am J Public Health. 2013;103(11): 2098–2105. 4. Siegel M, Negussie Y, Vanture S, Pleskunas J, Ross CS, King C. The relationship between gun ownership and stranger and nonstranger firearm homicide rates in the United States, 1981–2010. Am J Public Health. 2014; 104(10):1912–1919. 5. Miller M, Hemenway D. The relationship between firearms and suicide: a review of the literature. Aggress Violent Behav. 1999;4(1):59–75. 6. Miller M, Azrael D, Barber C. Suicide mortality in the United States: the importance of attending to method in understanding population-level disparities in the burden of suicide. Annu Rev Public Health. 2012;33(1): 393–408. 7. Miller M, Barber C, White RA, Azrael D. Firearms and suicide in the United States: is risk independent of underlying suicidal behavior? Am J Epidemiol. 2013; 178(6):946–955. 8. Wellford CF, Pepper J, Petrie C, eds. Firearms and Violence: A Critical Review. Washington, DC: National Academies Press; 2004.
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9. Miller M, Lippmann SJ, Azrael D, Hemenway D. Household firearm ownership and rates of suicide across the 50 United States. J Trauma. 2007;62(4):1029–1034, discussion 1034–1035. 10. Miller M, Azrael D, Hepburn L, Hemenway D, Lippmann SJ. The association between changes in household firearm ownership and rates of suicide in the United States, 1981–2002. Inj Prev. 2006;12(3):178–182. 11. Briggs JT, Tabarrok A. Firearms and suicides in US states. Int Rev Law Econ. 2014;37:180–188. 12. Birckmayer J, Hemenway D. Suicide and firearm prevalence: are youth disproportionately affected? Suicide Life Threat Behav. 2001;31(3):303–310. 13. Hemenway D, Miller M. Association of rates of household handgun ownership, lifetime major depression, and serious suicidal thoughts with rates of suicide across US census regions. Inj Prev. 2002;8(4):313–316. 14. Kaplan MS, Geling O. Firearm suicides and homicides in the United States: regional variations and patterns of gun ownership. Soc Sci Med. 1998;46(9):1227–1233. 15. Kleck G, Patterson EB. The impact of gun control and gun ownership levels on violence rates. J Quant Criminol. 1993;9(3):249–287. 16. Lester D. Firearm availability and the incidence of suicide and homicide. Acta Psychiatr Belg. 1988;88(5-6): 387–393. 17. Lester D. Gun control, gun ownership, and suicide prevention. Suicide Life Threat Behav. 1988;18(2):176–180. 18. Lester D. Gun ownership and suicide in the United States. Psychol Med. 1989;19(2):519–521. 19. Ludwig J, Cook PJ, eds. Evaluating Gun Policy: Effects on Crime and Violence. Washington, DC: Brookings Institution Press; 2003.
30. Kessler G. Fact checker: Obama’s claim that “states with the most gun laws tend to have the fewest gun deaths.” Washington Post. October 5, 2015. Available at: https://www.washingtonpost.com/blogs/fact-checker/ wp/2015/10/05/obamas-claim-that-states-with-themost-gun-laws-tend-to-have-the-fewest-gun-deaths. Accessed October 14, 2015. 31. Siegel MB, Rothman EF. Firearm ownership and the murder of women in the United States: evidence that the state-level firearm ownership rate is associated with the nonstranger femicide rate. Violence Gender. 2016; Epub ahead of print. 32. Siegel M, Ross CS, King C. A new proxy measure for state-level gun ownership in studies of firearm injury prevention. Inj Prev. 2014;20(3):204–207. 33. US Department of Commerce, Bureau of the Census. State area measurements and internal point coordinates. 2016. Available at: https://www.census.gov/geo/ reference/state-area.html. Accessed February 3, 2016. 34. US Department of Commerce, Bureau of Economic Analysis. Regional data: GDP and personal income. 2016. Available at: http://www.bea.gov/iTable/iTable.cfm? reqid=70&step=1&isuri=1&acrdn=2#reqid=70&step= 1&isuri=1. Accessed February 3, 2016. 35. Association of Religion Data Archives. US church membership data. Mars Hill, NC: Glenmary Research Center, 1980 and 1990; and Lenexa, KS: Association of Statisticians of American Religious Bodies, 2000 and 2010. Available at: http://www.thearda.com/Archive/ ChState.asp. Accessed February 24, 2016. 36. Cross CP, Copping LT, Campbell A. Sex differences in impulsivity: a meta-analysis. Psychol Bull. 2011;137(1): 97–130.
20. Markush RE, Bartolucci AA. Firearms and suicide in the United States. Am J Public Health. 1984;74(2): 123–127. 21. Mathur VK, Freeman DG. A theoretical model of adolescent suicide and some evidence from US data. Health Econ. 2002;11(8):695–708. 22. Miller M, Azrael D, Hemenway D. Firearm availability and unintentional firearm deaths, suicide, and homicide among 5–14 year olds. J Trauma. 2002;52(2): 267–274, discussion 274–275. 23. Miller M, Azrael D, Hemenway D. Firearm availability and suicide, homicide, and unintentional firearm deaths among women. J Urban Health. 2002;79(1):26–38. 24. Miller M, Hemenway D, Azrael D. Firearms and suicide in the northeast. J Trauma. 2004;57(3):626–632. 25. Miller M, Azrael D, Hemenway D. Household firearm ownership and suicide rates in the United States. Epidemiology. 2002;13(5):517–524. 26. Clarke RV, Jones PR. Suicide and increased availability of handguns in the United States. Soc Sci Med. 1989;28(8):805–809. 27. Duggan M. Guns and suicide. In: Ludwig J, Cook P, eds. Evaluating Gun Policy: Effects on Crime and Violence. Washington, DC: Brookings Institution Press; 2003: 41–67. 28. Kleck G. Point Blank: Guns and Violence in America. New Brunswick, NJ: Transaction Publishers; 2005. 29. Sloan JH, Rivara FP, Reay DT, Ferris JA, Kellermann AL. Firearm regulations and rates of suicide: a comparison of two metropolitan areas. N Engl J Med. 1990;322(6): 369–373.
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Firearm Ownership and Suicide Rates Among US Men and Women, 1981–2013 Michael Siegel, MD, MPH, and Emily F. Rothman, ScD, MS Objectives. To examine the relationship between state-level firearm ownership rates and gender-specific, age-adjusted firearm and total suicide rates across all 50 US states from 1981 to 2013. Methods. We used panel data for all 50 states that included annual overall and gender-specific suicide and firearm suicide rates and a proxy for state-level household firearm ownership. We analyzed data by using linear regression and generalized estimating equations to account for clustering. Results. State-level firearm ownership was associated with an increase in both male and female firearm-related suicide rates and with a decrease in nonfirearm-related suicide rates. Higher gun ownership was associated with higher suicide rates by any means among male, but not among female, persons. Conclusions. We found a strong relationship between state-level firearm ownership and firearm suicide rates among both genders, and a relationship between firearm ownership and suicides by any means among male, but not female, individuals. Policy implications. For male persons, policies that reduce firearm ownership will likely reduce suicides by all means and by firearms. For female persons, such policies will likely reduce suicides by firearms. (Am J Public Health. 2016;106:1316–1322. doi:10.2105/ AJPH.2016.303182)
A
pproximately 40 000 people die as a result of suicide each year in the United States, making it the 10th leading cause of death in the nation and costing approximately $44 billion per year.1,2 Although firearm homicide may be the most frequently reported aspect of firearm mortality by the press, the number of annual firearm suicides is almost twice as high as the number of firearm homicides. In 2013, there were 11 208 firearm homicides and 21 175 firearm suicides.1 Two recent studies demonstrated a strong association between levels of firearm ownership and rates of firearm homicide at the state level.3,4 We examined the relationship between state-level firearm ownership and state-specific suicide rates. Two major lines of research have explored the relationship between firearm prevalence and suicide rates.5–7 A number of individual-level studies have demonstrated that the presence of a firearm in the home increases the risk of suicide, both for the firearm owner and for household members.5
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However, these studies are limited because they only examine the individual risks of firearm ownership. They cannot be used to assess whether the prevalence of firearm ownership in the population affects suicide rates for an expanded geographical area. Moreover, the previous line of research has been criticized because of the possibility that people who live in households with firearms are inherently more likely to attempt suicide and that persons in a home in which a suicide has occurred may be more likely to recall firearm ownership.8,9 A second, complementary line of research addresses these limitations through crosssectional studies that correlate levels of firearm
ownership with rates of firearm suicide at the state or regional level. These studies have consistently found a relationship between increased levels of firearm ownership in a state or region and higher rates of firearm suicide.9–25 However, the results regarding the association between firearm ownership in a state or region and total suicide rates have been mixed, with several studies failing to find a relationship.15–17,26–29 This conflicting evidence led the National Research Council in 2004 to conclude that this association is more modest than the association between [individual] firearm ownership and firearm suicide; it is less consistently observed across time, place, and persons; and the causal relation remains unclear.8(p192)
Since the National Research Council report in 2004, 4 additional ecological studies have reported a significant association between higher levels of firearm ownership and overall suicide rates at the regional10 or state7,9,11 level. Still, 2 of these studies analyzed data for only a single year,7,9 limiting the generalizability of the findings. As recently as October 5, 2014, a Washington Post “fact checker” article reported that “studies have shown little connection between suicides and access to firearms.”30 In fact, most data used in the existing studies comprised only a cross-section in time; only 710,11,17,19,22,23,25 contained panel data over multiple years. Only 2 of the studies7,11 analyzed data subsequent to 2002, and none examined data more recent than 2009. Studies analyzing data over long time periods are valuable because they assess the
ABOUT THE AUTHORS
All of the authors are with the Department of Community Health Sciences, Boston University School of Public Health, Boston, MA. Correspondence should be sent to Michael Siegel, MD, MPH, Department of Community Health Sciences, Boston University School of Public Health, 801 Massachusetts Ave, 4th Floor, Boston, MA 02118 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This article was accepted March 2, 2016. doi: 10.2105/AJPH.2016.303182
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effects of variation in firearm availability not only between states but also within states over time. Recently, we advanced the field of firearms research by compiling a comprehensive database of state-level firearm ownership, firearm and total homicide rates, and 20 different sociodemographic control variables for the 30-year period from 1981 to 2010.3,4,31 Another important criticism of much of the existing literature on firearm ownership and suicide is that it has relied upon a proxy measure of state-level firearm ownership that correlates with survey measures of household firearm prevalence only at a level of 0.80.32 We recently developed an improved proxy measure for firearm ownership at the state level, which increases the correlation with surveymeasured household firearm prevalence from 0.80 to 0.95.32 This new proxy takes into account not only the proportion of suicides in which a firearm was used (a long-standing, validated measure of state-level firearm ownership), but also the state’s hunting license rate. A final limitation of the existing literature is that only 1 research group (5 studies) has examined the relationship between firearm ownership and firearm suicide rates separately by gender.7,9,10,24,25 The results are conflicting, with 1 study showing a stronger relationship for women,9 2 showing a stronger relationship for men,7,24 and 2 showing no difference.10,25 In this article, we expanded our existing database through 2013 and added data on gender-specific firearm and overall suicide rates by state for the entire period from 1981 to 2013. This study expands upon previous work by incorporating the most recent data, analyzing data over 3 decades, using a new and improved proxy for state-level firearm ownership, examining the relationship between firearm ownership levels and firearm suicide rates separately by gender, and controlling for the most extensive panel to date of annual, state-specific factors that could potentially confound the association between firearm ownership and suicide rates. We examined the relationship between firearm ownership and gender-specific, age-adjusted firearm and total suicide rates across all 50 states during the 33-year period 1981 through 2013, while controlling for region, urbanization, population density, proportion of Catholic adherents, per capita gross domestic product, per capita personal disposal income,
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household income, education, divorce rate, alcohol use, violent crime rate, nonviolent crime rate, and incarceration rate. To the best of our knowledge, this is the most comprehensive study to date, both in terms of the number of years in the analysis and the comprehensiveness of the control variables used.
METHODS For the 33-year period from 1981 to 2013, we assembled a panel of data for all 50 states that included annual overall and gender-specific suicide and firearm suicide rates and a proxy for state-level household firearm ownership. We investigated the relationship between the firearm ownership level in a state for a given year and the adjusted overall and firearm suicide rate in that state and year, with control for factors that could confound the association. We used a linear regression model, accounting for clustering of observations among years by entering fixed effects for each year. We accounted for clustering of observations among states by using a generalized estimating equations (GEE) approach. Our basic approach, including a detailed description of variables, data sources, and analytic methods, has been published previously.3
Variables and Data Sources The outcome variable was the ageadjusted, gender-specific overall, firearm, or nonfirearm suicide rate, obtained from the Centers for Disease Control and Prevention’s (CDC’s) Web-Based Injury Statistics Query and Reporting Systems database.1 As there were 33 years and 50 states, the total number of observations was 1650. However, we were limited by the small number of female firearm suicides in some states during some years. For the years 1999 to 2013, the CDC does not report data when the number of counts in a cell (e.g., female firearm suicides) is fewer than 10. Thus, we were missing data for 148 year–state observations, resulting in a final sample size of 1502 for the analyses of female suicide rates. The main predictor variable was the prevalence of household firearm ownership in a given state for a given year, measured by our new proxy variable.32 The use of a proxy is necessary because there are no state-level data
on firearm ownership for most of the study period. The Behavioral Risk Factor Surveillance System (BRFSS) has not collected state firearm ownership data since 2004.3 Previous studies have used a decent proxy: the percentage of suicides in which a firearm was used (firearm suicides divided by all suicides, or FS/S). However, the measure used in those previous studies correlates with survey measures of firearm ownership only at a level of 0.80.32 Our new proxy variable, which includes a state’s hunting license rate in addition to FS/S, improves this correlation to 0.95.32 The details of how our new proxy variable was validated are available here.32 The major problem with the traditional proxy is that it tends to overestimate household gun ownership in states with low hunting license rates and to underestimate household gun ownership in states with high hunting license rates. The correlation between hunting license rates and survey measures of state household gun ownership is 0.80. By accounting for hunting licenses, the new proxy produces more accurate estimates. For example, in Hawaii, the state with the lowest hunting license rate, the BRFSS gun prevalence estimate for 2001 is 9%, the old proxy is 23%, and the new proxy is 10%. In South Dakota, the state with the highest hunting license rate, the BRFSS gun prevalence estimate for 2001 is 57%, the old proxy is 41%, and the new proxy is 53%. We controlled for the following state-level factors, which could potentially be related both to firearm ownership and suicide rates: level of urbanization, educational attainment, unemployment, median household income, per capita alcohol consumption, nonhomicide violent crime rate (aggravated assault, robbery, and forcible rape), nonviolent (property) crime rate (burglary, larceny theft, and motor vehicle theft), incarceration rate, and divorce rate. To control for differences in suicide rates by region, we included indicator variables for the 4 US Census regions (Northeast, Midwest, South, and West). To further control for urban–rural differences, we included population density for each state, obtained from the US Census.33 To control for differences between states and over time in the state of the economy we included 2 measures: (1) the per capita gross domestic product, and (2) the per capita personal disposable income. These measures
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were obtained from the US Bureau of Economic Analysis.34 Finally, we controlled for the number of Catholic adherents per 1000 persons in each state by using data from the Association of Religion Data Archives35 for the years 1980, 1990, 2000, and 2010 and interpolating to derive estimates for the intervening years.
Model and Statistical Analysis Our outcome variable—age-adjusted suicide rates—was approximately normally distributed. Therefore, we used a linear regression model, which follows the approach used in several previous studies.7,11–13,24,27 Because our data were a panel with multiple observations each year (n = 50) and multiple years of state data (n = 33), there were 2 sources of clustering. To account for clustering by year, we included year as a fixed effect in the regression models. To account for clustering among states, we used a GEE approach with robust variance estimators. This follows the approach taken by Miller et al. to account for clustering by region.25 In the GEE models, we tested a variety of assumptions about the nature of the working correlation matrix. We chose the model with the best fit—a correlation matrix with an autoregressive structure—by selecting the model with the lowest quasilikelihood under the independence model criterion. We ran 2 models: (1) a full model that included all state-level variables, and (2) a parsimonious final model that only included variables significant according to a Wald test at a level of .05, produced with a backward stepwise regression procedure. To ease the interpretation of regression coefficients, we present the estimated changes in suicide rates associated with an increase of 10 percentage points in a state’s firearm ownership prevalence. We conducted all analyses with the GENMOD procedure in SAS version 9.3 (SAS Institute Inc, Cary, NC).
RESULTS Over the 33-year study period, the mean estimated percentage of firearm ownership ranged from a low of 12.2% in Hawaii to a high of 72.8% in Wyoming, with an average overall for all states of 41.0% (Table 1).
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TABLE 1—Mean Average Household Firearm Ownership Rate and Gender-Specific, Age-Adjusted Firearm-Related Suicide Rates, by State: United States, 1981–2013 Average Firearm Suicide Rate, 1981–2013 (per 100 000) State United States
Average Firearm Ownership, % (Rank)
Male (Rank)
Female (Rank)
41.0
14.2
2.1
Hawaii
12.2 (1)
4.8 (3)
0.5 (4)
Massachusetts
13.9 (2)
4.2 (1)
0.4 (3)
Rhode Island
15.5 (3)
5.2 (5)
0.6 (5)
New Jersey
16.9 (4)
4.5 (2)
0.4 (2)
Connecticut
21.6 (5)
6.4 (6)
0.7 (6)
New York
21.7 (6)
5.1 (4)
0.4 (1)
Illinois
25.0 (7)
7.8 (7)
0.9 (7)
California
26.6 (8)
10.7 (11)
1.6 (19)
Delaware
28.1 (9)
10.6 (10)
1.2 (13)
Maryland
30.9 (10)
9.9 (8)
1.1 (10)
Florida
32.3 (11)
14.2 (24)
2.6 (34)
Washington
34.0 (12)
13.6 (21)
2.0 (25)
Ohio
34.3 (13)
11.4 (13)
1.5 (18)
New Hampshire
35.1 (14)
12.1 (18)
1.7 (20)
Indiana
37.5 (15)
13.5 (20)
1.7 (21)
Iowa
37.7 (16)
11.3 (12)
1.1 (11)
Colorado
38.4 (17)
17.1 (38)
2.5 (32)
Pennsylvania
38.4 (18)
11.5 (14)
1.3 (15)
Nevada
38.8 (19)
24.4 (49)
4.2 (50)
Minnesota
39.1 (20)
10.2 (9)
0.9 (8)
Arizona
39.5 (21)
19.2 (44)
3.2 (47)
Michigan
39.6 (22)
11.7 (16)
1.3 (14)
New Mexico
40.5 (23)
20.8 (46)
3.0 (42)
Virginia
40.6 (24)
14.5 (26)
2.1 (27)
Texas
41.7 (25)
14.4 (25)
2.5 (33)
Kansas
41.8 (26)
14.1 (23)
1.8 (22)
Nebraska
42.1 (27)
11.8 (17)
1.4 (16)
North Carolina
42.5 (28)
15.1 (29)
2.4 (29)
Wisconsin
42.8 (29)
11.6 (15)
1.2 (12)
Oregon
43.4 (30)
16.9 (35)
2.5 (31)
Utah
43.5 (31)
17.4 (41)
2.2 (28)
Missouri
43.6 (32)
15.2 (30)
1.9 (24)
South Carolina
44.6 (33)
15.0 (27)
2.7 (37)
Georgia
44.8 (34)
16.0 (31)
2.8 (38)
Oklahoma
46.6 (35)
17.2 (39)
3.0 (41)
Kentucky
48.6 (36)
17.7 (42)
2.7 (35)
Louisiana
48.6 (37)
16.3 (32)
3.1 (44)
Maine
48.7 (38)
14.0 (22)
1.8 (23)
Continued
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TABLE 1—Continued Average Firearm Suicide Rate, 1981–2013 (per 100 000) State
Average Firearm Ownership, % (Rank)
Male (Rank)
Female (Rank)
Alabama
49.7 (39)
16.7 (34)
3.0 (43)
North Dakota
51.1 (40)
13.0 (19)
1.0 (9)
Tennessee
51.7 (41)
16.9 (37)
2.9 (40)
Vermont
53.2 (42)
16.9 (36)
2.1 (26)
Mississippi
53.7 (43)
16.4 (33)
3.1 (45)
Arkansas
55.1 (44)
17.4 (40)
2.9 (39)
Alaska
56.0 (45)
20.7 (45)
3.7 (48)
West Virginia
56.8 (46)
18.4 (43)
2.4 (30)
South Dakota
60.6 (47)
15.0 (28)
1.4 (17)
Idaho
61.6 (48)
21.0 (47)
2.7 (36)
Montana
68.4 (49)
23.5 (48)
3.2 (46)
Wyoming
72.8 (50)
26.1 (50)
3.9 (49)
Among the 50 states, the average percentage of firearm ownership decreased from 45.6% in 1981 to 36.5% in 2013 (P < .01). Over the study period, the mean ageadjusted firearm suicide rate among male individuals ranged from a low of 4.2 per 100 000 in Massachusetts to a high of 26.1 per 100 000 in Wyoming, with an average over all states of 14.2 per 100 000 (Table 1). The mean age-adjusted firearm suicide rate among female individuals over the study period ranged from a low of 0.40 per 100 000 in New York to a high of 4.2 per 100 000 in Nevada, with an average over all states of 2.1 per 100 000. Among the 50 states, the average male firearm suicide rate decreased slightly from 14.5 per 100 000 in 1981 to 13.9 per 100 000 in 2013, and the average female firearm suicide rate decreased slightly from 2.6 per 100 000 to 2.3 per 100 000. The average percentage of suicides in which a firearm was used was consistently 1.6 times higher among male (62.0% over study period) than among female persons (39.1% over study period; P < .01; data not shown). Among both genders, the average proportion of suicides in which a firearm was used decreased by approximately 12% to 15% over the course of the study period, from 65.5% during 1981 to 1990 to 57.8% during 2000 to 2013 among male individuals and from 41.5% to 35.3% among female individuals. All of these decreases were statistically significant at the P < .01 level.
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In bivariate analyses, there was a strong correlation between state-level firearm ownership and the adjusted firearm-related suicide rate for both genders, with firearm ownership explaining 71% of the variation (R2 = 0.71) in the firearm suicide rate for male individuals and 49% of the variation (R2 = 0.49) in the firearm suicide rate for female individuals (Figures 1 and 2). In a bivariate analysis (a GEE linear regression model with year fixed effects and accounting for clustering by state, but without any predictor variables besides firearm ownership), the firearm ownership proxy was a significant predictor of male firearm suicide rates (increase of 3.3 per 100 000 for each 10-percentage-point increase in firearm ownership), male nonfirearm suicide rates (decrease of 2.2 per 100 000 for each 10percentage-point increase in firearm ownership), and total suicide rates (increase of 1.6 per 100 000 for each 10-percentage-point increase in firearm ownership; Table 2). For female individuals, the firearm ownership proxy was a significant predictor of firearm suicide rates (increase of 0.5 per 100 000 for each 10-percentage-point increase in firearm ownership) and nonfirearm suicide rates (decrease of 0.4 per 100 000 for each 10-percentage-point increase in firearm ownership), but was not associated with total suicide rates.
In the full multivariate GEE linear regression models, the firearm ownership proxy was a significant predictor of male firearm suicide rates (increase of 3.1 per 100 000 for each 10-percentage-point increase in firearm ownership), male nonfirearm suicide rates (decrease of 1.5 per 100 000 for each 10percentage-point increase in firearm ownership), and total suicide rates (increase of 1.9 per 100 000 for each 10-percentage-point increase in firearm ownership; Table 2). For female persons, the firearm ownership proxy was a significant predictor of firearm suicide rates (increase of 0.4 per 100 000 for each 10-percentage-point increase in firearm ownership) and nonfirearm suicide rates (decrease of 0.5 per 100 000 for each 10percentage-point increase in firearm ownership), but was not associated with total suicide rates. The same pattern emerged in the final models. To examine whether our use of a proxy for household firearm ownership explains the observed findings, we repeated the analyses in 2 ways: (1) using the traditional FS/S proxy, and (2) restricting the analysis to the years 2001, 2002, and 2004 and using BRFSS survey data on household firearm ownership. The positive relationship between gun ownership and the overall male suicide rate remained significant when we used the FS/S proxy (increase of 1.0 per 100 000 for each 10 percentage point increase in gun ownership) and when we used only survey data (increase of 1.7 per 100 000 for each 10-percentagepoint increase in gun ownership). The positive relationship between gun ownership and female firearm suicide rates also remained significant when we used the FS/S proxy (increase of 0.6 per 100 000 for each 10percentage-point increase in gun ownership) and when using only survey data (increase of 0.5 per 100 000 for each 10-percentage-point increase in gun ownership). In the final models, other covariates that consistently predicted higher suicide rates were West region, higher alcohol consumption, higher divorce rate, higher violent crime rate, lower population density, and lower per capita gross domestic product. Each of these variables was also significantly related to the main predictor variable (gun ownership).
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Adjusted FS Rate/100 000
30.0
25.0
20.0
15.0
10.0
5.0
0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Average Gun Ownership, % Note. FS = firearm suicide; y = 0.3209x + 1.022; R2 = 0.71.
FIGURE 1—Relationship Between Average State-Level Gun Ownership and Average Male Age-Adjusted Firearm Suicide Rate: United States, 1981–2013
firearm ownership in a state and higher firearm suicide rates for both genders. Among male individuals, we also found a significant association between higher firearm ownership and higher overall suicide rates, but this relationship did not hold for female individuals.
DISCUSSION To the best of our knowledge, this is the most comprehensive analysis of the relationship between firearm ownership and gender-specific suicide rates among the 50 US states. We found a strong relationship between higher levels of 4.5
Adjusted FS Rate/100 000
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Average Gun Ownership, % Note. FS = firearm suicide; y = 0.0517x – 0.0923; R2 = 0.49.
FIGURE 2—Relationship Between Average State-Level Gun Ownership and Average Female Age-Adjusted Firearm Suicide Rate: United States, 1981–2013
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Our study adds to the consistent finding that, among both genders, increased prevalence of firearms is associated with an increase in the firearm-specific suicide rate. The magnitude of this relationship is substantial. Based on our model, if the firearm ownership in Wyoming were 41.0% (the average for all states) instead of 72.8%, its male firearm suicide rate would be lower by 9.9 per 100 000 (a 38% decline), and its female firearm suicide rate would be lower by 2.2 per 100 000 (a 56% decline). Our findings also add to the evidence that higher gun ownership is associated with higher overall suicide rates among male persons. Based on our model, if gun ownership in Wyoming were at the average for all states (41.0%) instead of at 72.8%, the overall male suicide rate in Wyoming would be lower by 5.7 per 100 000 among male persons (a 16% decline). Unlike a number of previous studies,7,9,10,24,25 we did not find a relationship between gun ownership and overall suicide rates among female persons. Because of these conflicting results, this issue warrants further study. Some have questioned whether the association between firearm ownership and homicide deaths might be the result of a so-called “reverse association”—that is, because there are many homicides in an area, more people will obtain firearms to protect themselves from that threat. A strength of this study is that, unlike previous studies on the relationship between firearm ownership and homicide rates at the state level, the observed association between firearm ownership and suicide rates is unlikely to be attributable to a reverse association. Although it is plausible that people might acquire more firearms if there are more homicides occurring near them, it does not seem likely that people are responding to increased suicide rates in their area by going out to purchase more firearms for themselves. As Briggs and Tabarrok have argued, the only plausible source of reverse association is that an individual may purchase a gun specifically because of suicidal intent.11 However, this would have almost no effect on gun ownership levels.11 Thus, we believe that the observed association between increased firearm ownership and higher firearm suicide is a causal one.
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TABLE 2—Change in Firearm, Nonfirearm, and Total Age-Adjusted Suicide Rates (per 100 000 Population) Associated With a 10-Percentage-Point Increase in State-Level Firearm Ownership Rate—by Gender Unadjusted Modela (95% CI)
Adjusted Modelb (95% CI)
Final Modelc (95% CI)
Overall
+1.6* (+1.3, +2.0)
+1.9* (+1.3, +2.5)
+1.9* (+1.5, +2.4)
Firearm Nonfirearm
+3.3* (+3.0, +3.5) –2.2* (–2.5, –1.9)
+3.1* (+2.7, +3.5) –1.5* (–1.8, –1.2)
+3.1* (+2.7, +3.5) –1.6* (–1.9, –1.3)
Outcome Variable Male suicide rate
Female suicide rate Overall
+0.0 (–0.2, +0.3)
–0.0 (–0.2, +0.2)
–0.0 (–0.2, +0.2)
Firearm
+0.5* (+0.4, +0.6)
+0.4* (+0.3, +0.5)
+0.4* (+0.3, +0.5)
Nonfirearm
–0.4* (–0.6, –0.2)
–0.5* (–0.6, –0.3)
–0.4* (–0.6, –0.3)
Note. CI = confidence interval. The values in the table represent the estimated change in the specified suicide rate for each 10-percentage-point increase in the predictor variable. For example, a value of +1.6 indicates that there is an increase of 1.6 per 100 000 in the suicide rate for each 10-percentage-point increase in household firearm ownership (e.g., comparing a state with 30% firearm ownership rate to a state with 40% firearm ownership rate would indicate a suicide rate difference of 1.6 per 100 000). a Based on a generalized estimating equation linear regression model with year fixed effects and accounting for clustering by state, but without any predictor variables besides firearm ownership. b Controlled for region, level of urbanization, population density, educational attainment, unemployment, median household income, per capita alcohol consumption, proportion of Catholic adherents, nonhomicide violent crime rate (aggravated assault, robbery, and forcible rape), nonviolent (property) crime rate (burglary, larceny theft, and motor vehicle theft), incarceration rate, divorce rate, per capita gross domestic product, and per capita disposable personal income. c Parsimonious model including only variables significant at the P < .05 level. *P < .05.
confounder that would still be influential over and above what is already included in the models. Nevertheless, repeating this study with a longitudinal design would help to establish whether the observed relationship is a causal one.
Public Health Implications The public health implication of these findings is that reductions in the prevalence of firearms may be an effective strategy for reducing overall and firearm-related suicides among male persons and for reducing firearm-related suicides among female persons. As suicide is the 10th leading cause of death in the United States, and firearmrelated deaths and injuries are extraordinarily costly, reducing firearm-related selfinjury and suicide is a public health imperative. CONTRIBUTORS M. Siegel conceptualized the study, collected the data, and led the data analysis and writing. E. F. Rothman assisted with the study design, analytical plan, writing, and revisions.
HUMAN PARTICIPANT PROTECTION
There are at least 2 potential explanations for our observation of an increased suicide rate by any method among male persons in association with higher state-level firearm ownership prevalence. First, it may be that at least some suicides are impulsive and that the ease with which a person can obtain a highly lethal means of suicide (i.e., a firearm), the more suicides will be completed.6,25 The impulse to attempt suicide may wane relatively quickly, such that the lack of ease in finding a lethal means may allow enough time to pass so that the suicidal impulse subsides or intervention occurs.6,11 Second, as Miller et al. argue, overall suicide rates may be lowered by “reducing population-level access to lethal means.”6(p401) Several natural experiments have demonstrated that overall suicide rates may be reduced by eliminating lethal means, such as removing carbon monoxide from gas used in ovens and heaters in the United Kingdom, banning toxic pesticides in Sri Lanka, and reducing soldiers’ access to firearms on weekends in Israel.6 One possible explanation for why we failed to find an association between higher levels of gun ownership and higher overall suicide rates among female individuals is that women tend
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to be less impulsive than men, so the reduced availability of lethal means might not prevent suicide as the suicidal ideation is more stable. In contrast, men who have high impulsivity but do not have easy access to a lethal means might be more likely to experience a prompt resolution of their impulsive suicidal ideation such that the lack of a lethal means actually prevents suicide altogether.
Limitations There are several limitations of this study. First, we used a proxy measure of firearm ownership rather than self-report, survey-based measures. However, we used a well-established proxy variable that has a correlation of 0.95 with survey-measured gun ownership. To remedy this problem, the CDC should reinstate self-reported firearm ownership prevalence surveillance through its BRFSS survey. A second limitation is that this is a crosssectional study, so an unknown confounder may explain the observed relationship. However, because of the number and scope of predictor variables we included in our analysis, it is difficult to imagine a potential
Institutional review board approval was not needed for this study because secondary data sources were used.
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9. Miller M, Lippmann SJ, Azrael D, Hemenway D. Household firearm ownership and rates of suicide across the 50 United States. J Trauma. 2007;62(4):1029–1034, discussion 1034–1035. 10. Miller M, Azrael D, Hepburn L, Hemenway D, Lippmann SJ. The association between changes in household firearm ownership and rates of suicide in the United States, 1981–2002. Inj Prev. 2006;12(3):178–182. 11. Briggs JT, Tabarrok A. Firearms and suicides in US states. Int Rev Law Econ. 2014;37:180–188. 12. Birckmayer J, Hemenway D. Suicide and firearm prevalence: are youth disproportionately affected? Suicide Life Threat Behav. 2001;31(3):303–310. 13. Hemenway D, Miller M. Association of rates of household handgun ownership, lifetime major depression, and serious suicidal thoughts with rates of suicide across US census regions. Inj Prev. 2002;8(4):313–316. 14. Kaplan MS, Geling O. Firearm suicides and homicides in the United States: regional variations and patterns of gun ownership. Soc Sci Med. 1998;46(9):1227–1233. 15. Kleck G, Patterson EB. The impact of gun control and gun ownership levels on violence rates. J Quant Criminol. 1993;9(3):249–287. 16. Lester D. Firearm availability and the incidence of suicide and homicide. Acta Psychiatr Belg. 1988;88(5-6): 387–393. 17. Lester D. Gun control, gun ownership, and suicide prevention. Suicide Life Threat Behav. 1988;18(2):176–180. 18. Lester D. Gun ownership and suicide in the United States. Psychol Med. 1989;19(2):519–521. 19. Ludwig J, Cook PJ, eds. Evaluating Gun Policy: Effects on Crime and Violence. Washington, DC: Brookings Institution Press; 2003.
30. Kessler G. Fact checker: Obama’s claim that “states with the most gun laws tend to have the fewest gun deaths.” Washington Post. October 5, 2015. Available at: https://www.washingtonpost.com/blogs/fact-checker/ wp/2015/10/05/obamas-claim-that-states-with-themost-gun-laws-tend-to-have-the-fewest-gun-deaths. Accessed October 14, 2015. 31. Siegel MB, Rothman EF. Firearm ownership and the murder of women in the United States: evidence that the state-level firearm ownership rate is associated with the nonstranger femicide rate. Violence Gender. 2016; Epub ahead of print. 32. Siegel M, Ross CS, King C. A new proxy measure for state-level gun ownership in studies of firearm injury prevention. Inj Prev. 2014;20(3):204–207. 33. US Department of Commerce, Bureau of the Census. State area measurements and internal point coordinates. 2016. Available at: https://www.census.gov/geo/ reference/state-area.html. Accessed February 3, 2016. 34. US Department of Commerce, Bureau of Economic Analysis. Regional data: GDP and personal income. 2016. Available at: http://www.bea.gov/iTable/iTable.cfm? reqid=70&step=1&isuri=1&acrdn=2#reqid=70&step= 1&isuri=1. Accessed February 3, 2016. 35. Association of Religion Data Archives. US church membership data. Mars Hill, NC: Glenmary Research Center, 1980 and 1990; and Lenexa, KS: Association of Statisticians of American Religious Bodies, 2000 and 2010. Available at: http://www.thearda.com/Archive/ ChState.asp. Accessed February 24, 2016. 36. Cross CP, Copping LT, Campbell A. Sex differences in impulsivity: a meta-analysis. Psychol Bull. 2011;137(1): 97–130.
20. Markush RE, Bartolucci AA. Firearms and suicide in the United States. Am J Public Health. 1984;74(2): 123–127. 21. Mathur VK, Freeman DG. A theoretical model of adolescent suicide and some evidence from US data. Health Econ. 2002;11(8):695–708. 22. Miller M, Azrael D, Hemenway D. Firearm availability and unintentional firearm deaths, suicide, and homicide among 5–14 year olds. J Trauma. 2002;52(2): 267–274, discussion 274–275. 23. Miller M, Azrael D, Hemenway D. Firearm availability and suicide, homicide, and unintentional firearm deaths among women. J Urban Health. 2002;79(1):26–38. 24. Miller M, Hemenway D, Azrael D. Firearms and suicide in the northeast. J Trauma. 2004;57(3):626–632. 25. Miller M, Azrael D, Hemenway D. Household firearm ownership and suicide rates in the United States. Epidemiology. 2002;13(5):517–524. 26. Clarke RV, Jones PR. Suicide and increased availability of handguns in the United States. Soc Sci Med. 1989;28(8):805–809. 27. Duggan M. Guns and suicide. In: Ludwig J, Cook P, eds. Evaluating Gun Policy: Effects on Crime and Violence. Washington, DC: Brookings Institution Press; 2003: 41–67. 28. Kleck G. Point Blank: Guns and Violence in America. New Brunswick, NJ: Transaction Publishers; 2005. 29. Sloan JH, Rivara FP, Reay DT, Ferris JA, Kellermann AL. Firearm regulations and rates of suicide: a comparison of two metropolitan areas. N Engl J Med. 1990;322(6): 369–373.
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