Cross-Sectional Associations
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51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84
85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
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Almost all ecological studies using cross-sectional data, both within the
United States and across countries, have found that both gun suicide rates
and the fraction of suicides committed with a gun are higher in geographic
areas with a higher prevalence of household gun ownership. This association
has been reported by investigators across the spectrum of the gun
control debate. It has been found across cities, states, regions, and nations
(Kleck and Patterson, 1993; Azrael et al., 2004; Killias, 2001), and it contrasts
with the more variable association between gun ownership rates and
the fraction of homicides committed with a gun.
1Studies were identified using various search engines, by a search for book chapters and
unpublished studies identified through personal communication with researchers in the field,
and by review of the reference lists of previous publications. A particular effort was made to
find studies in the firearms policy literature, reviewed for other chapters of this volume, which
may have examined suicide as a secondary focus of the investigation.
However, the most important policy question is not whether gun access
increases the risk of gun suicide, but whether gun access increases the
overall risk of suicide. Many cross-sectional studies have reported a positive,
bivariate association between gun ownership rates and overall suicide
rates across cities, states, and regions of the United States, but the relationship
is much smaller and less precise than the association between gun
ownership rates and gun suicide rates. The association between gun ownership
and overall suicide also appears to be sensitive to the details of the
measures and the statistical models being used.
U.S. Studies
Several ecological studies by Birckmayer and Hemenway (2001) and by
Miller et al. (2002a, 2002c) have focused on age-specific suicide rates by
region and state. Their gun ownership measures include survey estimates of
handgun and overall gun ownership from the GSS and, as a proxy measure,
the fraction of suicides committed with a firearm. Before controlling for
other social variables, Birckmayer and Hemenway find a positive association
between regional GSS-reported rates of gun ownership and age-specific
rates of suicide in every age group. After controlling for divorce, education,
unemployment, urbanization, poverty, and alcohol consumption, they find
a modest positive association between gun ownership and suicide risk for
youth ages 15 to 24 (b = .35, 95% confidence interval .05 to .65) and for
adults age 65 and over (b = .62, 95% C.I. .40-.84), but not for working-age
adults between ages 25 and 64. Subsequent studies from the same research
group use other model specifications, with varying results. For example,
Miller et al. (2002a) do not incorporate control variables; they find a
positive association between gun ownership and overall suicide rates in all
age groups (incidence rate ratio 1.14; 95% CI 1.01-1.24) and a negative
association between gun ownership and nongun suicide (IRR .87, 95% CI
.77-.97) that is more pronounced for persons 45 years and older, suggesting
greater substitution among methods in older age groups.
Duggan (2003) undertook a similar age-specific analysis, using subscriptions
to the gun magazine Guns & Ammo as his proxy for gun ownership.
Like Miller et al., Duggan did not include other covariates in his
regression models and, like Miller et al., he found a positive and significant
bivariate association between gun ownership and suicide across states. But
Duggan also found a significant positive association between gun magazine
subscription and nongun suicide for youth ages 10 to 19. The association
between the gun proxy and nongun suicide shifts from positive to negative
between ages 20 and 69 and becomes negative and statistically significant
for persons over age 69. He concludes that the positive association between
gun magazine subscriptions and nongun suicide among youth is evidence
TABLE 7-1 Ecological Studies of Associations Between Firearms
Prevalence and Suicide in the United States
Unit of Gun Subjects;
Source Analysis Measure Strata
Duggan 50 states Proxy: Guns 10 yr. age
(2003) 1996 & Ammo groups
Hemenway 9 regions Survey: GSS
and Miller 1988-1997 (household
(2002) handgun
ownership)
Miller et al. 9 regions Survey: GSS, Children
(2002b) 50 states BRFSS 5-14
1988-1997 Proxy: Cook
index, FS/S
(adult only)
Miller et al. 9 regions Survey: GSS, Adult
(2002c) 50 states BRFSS women
1988-1997 Proxy: Cook
index , FS/S
Miller et al. 9 regions Survey: GSS, 10-yr. age
(2002a) 50 states BRFSS groups
1988-1997 Proxy: Cook
index, FS/S
Birckmayer 9 regions GSS 10-yr age
and 1979-1994 groups
Hemenway
(2001)
Azrael et al. 9 regions Survey: GSS,
(2004) 50 states BRFSS, HICRC
1994-1998 Proxies: FS/S,
UFDR,
Guns & Ammo,
NRA
membership
continued
Results: Results: Results:
Guns and Guns and Guns and
Control Gun Nongun Overall
Variables Suicides Suicides Suicides
None all ages + 10-19: + all ages +
20-69: 0
70+: –
Major + – +
depression,
suicidal
thoughts, and
urbanization, OR
education, OR
unemployment,
OR
alcohol
consumption
Poverty, + 0 +
education,
urbanization
Poverty, + BRFSS:+ +
urbanization Others: 0
None all ages + <45: 0 all ages +
45+: –
Divorce, 15-24: + 0 15-24: +
education, 25-44: 0 25-64:0
unemployment, 45-84: + 65+: +
urbanization
None + n/a n/a
TABLE 7-1 Continued
Unit of Gun Subjects;
Source Analysis Measure Strata
Kaplan and 9 regions Survey: GSS Sex race
Geling 1989-1991
(1998)
Kleck and 170 U.S. OLS proxy:
Patterson cities gun crimes
(1993) IV proxy:
gun sport
Sloan et al. 2 cities Registry: Two age
(1990) 1985-1987 handguns groups,
Proxies: Cook race, sex
index
Strictness of gun
laws
Lester 48 states Proxy: gun
(1989) 1980 magazines
Lester 6 (of 7) Survey-household
(1988a) Australian gun ownership
states
Lester 9 regions Survey
(1988b) 1970 Proxy: gun laws
Lester 48 states Proxies: gun
(1987a) 1970 laws, UFDR
Proxy: Cook
index
Duggan 50 states Proxy: guns All ages
(2003) ammo sales rate
continued
Results: Results: Results:
Guns and Guns and Guns and
Control Gun Nongun Overall
Variables Suicides Suicides Suicides
None + Male:- n/a
Female: 0
Community traits: + 0 OLS: +
race, sex, age IV: 0
unemployment
rate, poverty,
income, home
ownership,
college
enrollment,
transience,
population
change, divorce,
place of worship,
etc.
None + – 0
None + 0 +
None 0 – 0
% black, median + 0 0
age, % urban,
divorce rate
None + UFDR:– 0
Other: 0
State, year fixed 0 0 0
effects
for an omitted variable, because any plausible causal effect of gun ownership
should be independent of, or negatively associated with, the nongun
suicide rate. There are several other possible explanations for Duggan’s
results; most obviously, it may be that Guns & Ammo subscribers are not
representative of all gun owners; his arguments about confounding would
also have been strengthened by the inclusion of some observable covariates.
All the same, both Miller’s and Duggan’s results support the view that
different gun proxies may yield different results, and all of the age-stratified
studies suggest that instrumentality effects, substitution, and omitted variables
may be playing different roles at different ages.
The most comprehensive effort to control for confounding factors was
published a decade ago. Kleck and Patterson (1993) undertook a crosssectional
study of the effect of firearms prevalence on crime rates and
firearm-related fatalities in 170 U.S. cities. Although the study did not
consider differences by age, the models included a set of 38 control variables
previously identified as predictors of violence rates. Like other investigators,
these authors found that higher levels of the proxy for gun owner-
TABLE 7-1 Continued
Unit of Gun Subjects;
Source Analysis Measure Strata
Mathur and 48 states Gun dealers Adolescent
Freeman per capita suicide
(2002) (15-19)
Azrael et al. 9 regions Survey: GSS
(2004) 50 states Proxy: FS/S
Clarke and Entire Survey: Gallup Type of
Jones United poll, GSS gun
(1989) States
NOTES: +, - indicate positive or negative effect (respectively), statistically significant at p <
.05; 0 indicates not significant.
BRFSS = Behavioral Risk Factor Surveillance System; GSS = General Social Survey; FS/S =
ratio of firearm suicide/total suicides; Cook Index = mean of firearm suicide/total suicide and
firearm homicide/total homicide; HICRC = Harvard Injury Control Research Center; UFDR
ship predicted higher rates of suicide (b = .132, p < .05). Kleck and Patterson
also found evidence that there might be a different association between
suicide risk and sporting gun ownership and suicide risk and defensive gun
ownership. In particular, they found no significant effect of sporting gun
ownership on the risk of suicide.
International Studies
Like the U.S. studies, the existing cross-national surveys have looked
for an association between rates of household gun ownership, overall suicide
rates, and the fraction of suicides committed with a gun. And, like the
U.S. studies, cross-national studies have found a consistent association between
gun ownership and the fraction of suicides committed with a gun
across countries; but in contrast to the U.S. studies, the cross-national
surveys do not reveal a consistent association between gun ownership and
overall suicide rates.
= unintentional firearm death rate; FLFP = female labor force participation; OLS = ordinary
least squares; IV = instrumental variable (two-stage least squares); NRA = National Rifle
Association.
When only one result is listed in column, all gun measures gave similar results. When
reported results include models both with and without covariates, only results with covariates
are presented.
Results: Results: Results:
Guns and Guns and Guns and
Control Gun Nongun Overall
Variables Suicides Suicides Suicides
State, year fixed Not stated Not stated +
effects
FLFP, divorce,
alcohol
consumption
family & cohort
size
Regional fixed + Not stated Not stated
effects
None Handgun + n/a
All guns: 0 All guns: 0
Handgun: +
Although gun ownership rates in the United States are much higher
than in most other developed countries, the rates of suicide in the United
States rank in the middle. Killias (1993), Killias (2001), and Johnson et al.
(2000) found that reported rates of household gun ownership were strongly
correlated with the fraction of suicides committed with a gun in each country
(Spearman’s rho = .79 to .92, p < .001). But the cross-country correlations
between household gun ownership and overall rates of suicide have
proven to be smaller and statistically imprecise (Spearman’s rho .25, p =
.27) (Killias, 2001). Likewise, in an often-cited study, Sloan et al. (1990)
compared the rates of gun and nongun suicides in Seattle, Washington,
with suicide rates in Vancouver, British Columbia, between 1985 and 1987;
they found higher rates of gun ownership are associated with higher rates of
gun suicide, lower rates of nongun suicide, and no significant difference in
the overall suicide rate between the two cities (relative risk .97, 95% CI .87
to 1.09).
Associations Between Gun Ownership and Suicide Rates Across Time
The fraction of suicides in the United States that are committed with a
firearm has increased from just over 35 percent in the 1920s to about 60
percent in the 1990s. Four studies have attempted to link this change in the
fraction of gun suicides with changes in gun ownership across time.
Three of these four studies have found positive associations between
proxies for gun ownership and the fraction of suicides committed with a
gun, but only one study, focusing on youth suicide, found an association
between gun ownership and overall suicide rates. Clarke and Jones (1989),
examined the national prevalence of household gun ownership reported in
polls by Gallup and the National Opinion Research Center between 1959
and 1984, comparing these reports with aggregate U.S. suicide rates over
the same period. This study found a positive association between the fraction
of households owning a handgun and the fraction of suicides committed
with a gun (b = .68, p = .001), but no association between household
gun ownership and overall risk of suicide (b = .04, p = .85). Azrael et al.
(2004) also report a strong linear association between individual and household
rates of gun ownership within regions and the fraction of suicides
committed with a gun between 1980 and 1998, with cross-sectional beta
coefficients ranging from .55 (for individual handgun ownership) to 1.02
(for household gun ownership of any kind), and an inter-temporal coefficient
between FS/S and household gun ownership of .905 (s.e. = .355). They
did not report the association between gun ownership and overall risk of
suicide. Mathur and Freeman (2002) used state-level per capita gun dealership
rates to predict adolescent suicide rates from 1970 to 1997. After
controlling for state and year fixed effects and number of other observed
covariates (e.g., divorce rates, per capital alcohol consumption, female labor
force participation, family size, and cohort size), Mathur and Freeman
found that increases in gun dealerships per capita predicted increases in the
overall youth suicide rate. Finally, Duggan (2003) used two decades of gun
magazine sales with controls for state and year fixed effects to explain the
trends in suicide rates across all age groups. Duggan found no association
between magazine subscription rates and either gun suicide or overall suicide
rates across time (b = .046, s.e. = .064, and b = .004, s.e. = .051,
respectively).
Assessment of Ecological Studies
Overall, the body of ecological studies has firmly established that firearms
access is positively associated with gun suicide, but the association
between firearm access and overall suicide is less certain.
In particular, gun suicide rates are strongly correlated with gun prevalence
across space and possibly across time, in the United States and across
countries. Likewise, many ecological studies do report a cross-sectional
association between gun ownership rates and overall suicide rates in the
United States. However, gun ownership rates do not seem to explain overall
suicide trends across countries or across time in the United States. Moreover,
the results seem to vary according to the firearm measure used, the
age group being studied, and the covariates included.
To further improve our understanding of the effects of firearms on suicide,
researchers need to be increasingly sensitive to the possibility of confounding
factors and substitution. Moreover, these ecological studies introduce two
additional problems that must be considered. First, the analyses are conducted
at the aggregate level, rather than at the individual level, and second, direct
measures of access to firearms are often not available, thus forcing researchers
to rely on proxies. We consider each of these issues in turn.
Substitution and Confounders
As with all empirical analyses, researchers and policy makers must be
sensitive to unobserved confounders when attempting to draw causal inferences
(see Box 7-1). To what extent would suicidal persons substitute other
methods if firearms were less available? Unmeasured and confounding factors
associated with both suicide risk and gun ownership might lead to a
spurious association between guns and suicide. For example, if persons
who are prone to own guns because of their mistrust of others were also at
greater risk for suicide, whether or not they owned guns, there could be a
noncausal statistical association between gun ownership and suicide. Likewise,
high levels of “social capital” might be associated with lower rates of
defensive gun ownership and lower suicide rates (Hemenway et al., 2001).
Neighborhood levels of gun ownership could even conceivably be affected
by neighborhood suicide rates: suicide rates might contribute to a
community’s perceived level of violence, whether people are aware of making
such a link or not.
This concern is not unique to ecological studies, but has been generally
ignored in this literature. There have been few systematic efforts to explore
or model possible confounders of the association between gun ownership
and suicide risk. Two studies by Hemenway and associates are suggestive.
First, Hemenway et al. (2001) investigated the hypothesis that persons who
live in communities with higher levels of mutual trust may be at lower risk
of suicide (because of increased social support), and lower risk of gun
ownership and less likely to own firearms (because of decreased motivation
for defensive gun ownership). They found that, across U.S. states, lower
levels of mutual trust and civic engagement, as reported on the General
Social Survey and on the Needham Lifestyle Survey, were associated with a
higher fraction of suicides committed with a gun. This study did not examine
the association between social capital, firearm ownership, and overall
suicide rates. Hemenway and Miller (2000) investigated the hypothesis that
regions with higher rates of firearm ownership were characterized by higher
rates of major depression, which is known to be an important independent
risk factor for suicide. They found that the cross-sectional, regional association
between firearm ownership and suicide rates was not explained by
differences in the regional prevalence of major depression and serious suicidal
thoughts.