Psychological Autopsy Studies
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A number of studies have now been published that compare the prevalence
of firearms in the homes of suicide victims with the prevalence of
firearms in the homes of living controls; these studies, most of which make
use of a “psychological autopsy” case-control design, are summarized in
Table 7-3. Psychological autopsy studies are retrospective studies using
interviews with relatives, neighbors, coworkers, or other close contacts of a
deceased person (or of a living control subject) seeking to reconstruct the
presence or absence of behavioral or psychological risk factors that may
have predisposed the death. All of the studies that the committee reviewed
have found a positive association between household gun ownership and
suicide risk, although the magnitude of the estimated association varies.
Although more recent studies have used better data collection strategies and
more appropriate study samples (e.g., Conwell et al., 2002; Beautrais et al.,
1996), the earlier studies suffer from methodological problems—ranging
from sample selection problems to measurement bias, small samples, and
TABLE 7-3 Psychological Autopsy Studies of Firearm Prevalence
and Suicide
Cases Controls
Source N n
Conwell et al. Older adult Community
(2002) suicides controls
N = 86 n = 86
Shah et al. Adolescent School-selected
(2000) gun suicides controls
N = 36
n = 36
Brent et al. Adolescent Community
(1999) suicides controls
N = 140a n = 131
Bailey et al. Female Community
(1997) homicides and controls
suicides in
the home
N = 123 n = 266 pairs
suicides; 143
homicidesa
Beautrais et al. Suicides Community
(1996) controls
N = 197 n = 1,028 normal
controls
Brent et al. Adolescent Community
(1994) suicides with controls with
affective affective disorder
disorder n = 23
N = 63a
continued
Result: Gun
Gun Covariates, Matching Access and Overall
Measure Factors Suicide Risk
Firearm in Education, living situation, +: any gun, handgun
home psychiatric illness 0: long gun
Matching: age, race, sex,
county of residence
Firearm in Previous mental health n/a: no information
the home problems, alcohol use, about overall suicide
conduct disorder
(although gun is +
Matching: age, sex, school associated with risk
of gun suicide)
Firearm in Psychiatric diagnosis, +: any gun
the home family history, life
stressors, history of abuse
Matching by sex; age, race,
county of origin,
socioeconomic status
Firearm in Mental illness; history of +: any gun
the home domestic violence; alcohol
use, alcohol problems,
prior arrest; illicit drug use;
home security
Matching: neighborhood,
sex, race, age
Firearm in Age, gender, ethnicity, 0: gun not
the home psychiatric diagnosis associated with
overall risk of
suicide
(although gun is
associated with risk
of gun suicide)
Firearm in Psychiatric diagnosis, +: any gun, handgun
the home family history, stressful 0: not long gun
life events, past treatment
Matching: age, sex, county
of origin, socioeconomic
status
TABLE 7-3 Continued
Cases Controls
Source N n
Bukstein et al. Adolescent Community
(1993) suicides with controls with
substance substance abuse
abuse
N = 23a
n = 12
Brent et al. Adolescent Community
(1993a) suicides controls
N = 67a n = 67
Brent et al. Adolescent Community
(1993b) suicides controls without
N = 67a psychiatric
disorder
n = 38
Kellermann et al. Suicides in Community
(1992) the home controls
N = 438b n = 438
Brent et al. Adolescent Inpatient controls
(1991) suicides
n = 94
N = 47a 47 attempters,
47 never-suicidal
Brent et al. Adolescent Inpatient controls
(1988) suicides n = 56
N = 27
aOverlapping samples, western Pennsylvania.
bOverlapping samples, King County, Washington, and Shelby County, Tennessee.
Result: Gun
Gun Covariates, Matching Access and Overall
Measure Factors Suicide Risk
Firearm in Psychiatric diagnosis, +: any gun, handgun
the home family history, stressful 0: not long gun
life events, past treatment 0: not gun storage
Matching: age, race, sex,
socioeconomic status,
county of residence
Firearm in Psychiatric diagnosis +: any gun,
the home handgun
Matching: age, sex,
socioeconomic status, •particularly when
county of origin no psychiatric
disorder is present
Firearm in Psychiatric diagnosis, +: any gun, loaded
the home family history, stressful gun
life events •particularly when
Matching: age, sex, county no psychiatric
of origin, socioeconomic disorder is present
status
Firearm in Alcohol use, illicit drug +: any gun
the home use, domestic violence,
living alone, education, •particularly when
previous hospitalization no psychopathology
due to alcohol, current is reported
psychiatric medication.
Matching: age, race, sex,
neighborhood
Firearm in Psychiatric diagnosis, +: any gun
the home family history; female
headed household, treatment 0: Not gun storage
history
Matching: age, sex, county
of origin
Firearm in Precipitants, psychiatric +: any gun
the home diagnosis, family history,
exposure to suicidal contact
failure to control for possible confounders—which raise doubts about the
reliability and interpretation of the findings that have been reported to date.
By far the largest psychological autopsy studies of guns and suicide,
homicide, and unintentional injury have been conducted by Kellerman et al.
(1992, 1993, 1998; Bailey et al., 1997). Their 1992 study of firearms and
suicide is representative of their approach. Cases occurred in King County,
Washington, and Shelby County, Tennessee, and were selected for study if
the suicide took place in or near the home of the victim, regardless of
method of suicide used; out of 803 suicides occurring during the study
period, 565 occurred in the home and 238 occurred elsewhere. Cases were
matched with living controls of the same race, sex, and age range and
residing in the same neighborhood; the team sought to interview proxy
respondents for both cases and controls, but 50 percent of the control
interviews were conducted with the (living) subjects themselves. The structured
interviews screened for substance abuse, domestic violence, legal problems,
current medications, and history of depression, as well as the presence
or absence of a gun in the home, but the protocols did not make formal
psychiatric diagnoses. The odds ratio associated with firearms ranked fifth
among the seven variables that were included in the final conditionallogistic
regression analysis; the seven measures, along with their adjusted
odds ratios, included psychotropic medication prescribed (35.9), previous
hospitalization due to drinking (16.4), active use of illicit drugs (10.0), lives
alone (5.3), gun kept in household (4.8), failure to graduate from high
school (4.1), and drinks alcohol (2.3). The adjusted odds ratio for gun
access had a 95 percent confidence interval of 2.7 to 8.5. Guns were a
stronger risk factor for suicide among the 63 case subjects with no history
of depression or mental illness (odds ratio 32.8; 95 percent confidence
interval 4.6 to 232.8). According to the proxy informants, only 3 percent of
suicides in the sample had purchased a gun within two weeks before death.
This team’s focus on suicide in the home would have been appropriate
for a study of unintentional injuries. However, the element of intention
leads to an important difference between a study of “suicide and guns in the
home” (which would be the usual policy question) and a study of “guns
and suicide in the home” (which is what the research group elected to
study), because it is likely that decisions about method and location of
suicide are made together. This means that a study of gun access in a study
restricted to suicides that take place in the home may be no more informative
than a study of bridge access in a study restricted to suicides that take
place from a bridge.
The possibly biased sample selection strategy, as well as other problems
in the execution of the study and reporting of results, provoked a storm of
attacks on the research team, the federal funding agency, and the medical
journal in which the reports were published. It is difficult to determine the
degree of bias that was actually introduced in these studies by the sample
selection strategy. However, one does learn that 58 percent of suicides
taking place in the victim’s home occurred by firearm, as did 46 percent of
suicides not in the home. An informal calculation using assumptions that
are favorable to the investigators suggests that omission of suicides taking
place outside of the home may have led to an overstatement of the true
relative risk by about 20 percent.7 There are other problems with the
execution of this study that may have actually led to biases of larger magnitude.
For example, after eliminating the suicides that occurred outside the
home, the investigators collected complete data for only 360 of 565 eligible
cases, so that the final results were based on only 64 percent of the sample
of suicides in the home and only 40 percent of the total suicide sample.
Several psychological autopsy studies have now focused on the risk of
suicide among adolescents. There are three important reasons for selecting
adolescents as a population for special scrutiny. First, suicide is the third
leading cause of death among adolescents; if reducing access to firearms were
a feasible way to reduce adolescent suicide, this would have great public
health importance. Second, it is likely that “impulsive” suicides are more
common among the young, so that studies of youth suicide may generalize to
the type of suicide for which preventive efforts seem most promising. And
third, studies of adolescent suicide are less susceptible to problems of reverse
causality: because adolescents under the age of 18 are not allowed to pur-
7We do not have enough information to calculate a matched odds ratio, but an unmatched
ratio can give a rough idea of the possible sampling bias. The investigators tell us that 65
percent of case subjects had guns in their home, compared with 41 percent of matched
controls. This basic information implies an unmatched odds ratio for suicides in the home of
2.67 = (65/35)/(41/59).
How might the results change if we consider all suicides, not just those in the home? There
were 238 suicides occurring outside the home during the observation period; 109, or about
45.8 percent of these suicides were committed with a firearm (compared to 57.7 percent
among suicides occurring in the home). We do not know the fraction of these suicide victims
who owned firearms. Assume, however, that that gun suicide probability by ownership status
does not depend on whether the suicide occurs inside or outside the home. Then, from
Kellerman et al., we know that 86 percent of suicidal owners used a gun and 6 percent of
suicidal nonowners used a gun. Using the law of total probability, we know that the fraction
of suicides committed with a firearm (0.458) can be decomposed into a weighted average of
the fraction committed by owners (0.86) and nonowners (0.06), where the weights depend on
the unknown fraction of owners. This implies that about 50 percent of out-of-home victims
owned firearms, and that 60 percent of all victims owned firearms. Under these assumptions,
the unmatched odds ratio comparing total suicides with control group equals 2.16 = (60/40)/
(41/59); if out-of-home suicides had been included in the sample, the crude odds ratio might
have been reduced by nearly 20 percent. The results are clearly sensitive to the assumption
that the rates of gun suicide by ownership do not vary by the location of the suicide. If
instead, one-quarter of suicidal nonowners used a gun (rather than 6 percent), the odds ratio
would equal approximately 1.83, about 31 percent less than that reported by the authors.
chase long guns or handguns in any state, an association between household
gun ownership and adolescent suicide cannot be attributed to the adolescent’s
suicidal plan. Six overlapping studies have been published by Brent and
colleagues based on cases of adolescent suicide occurring in western Pennsylvania.
The most recent report includes all of the adolescent suicides that have
been investigated by this research team and can serve as a summary of the
studies to date. Subjects were a consecutive series of 140 adolescent suicide
victims from western Pennsylvania and 131 community controls who were
matched to the group of suicide victims on age, race, gender, county of origin,
and socioeconomic status. Family members were interviewed using a structured
protocol concerning the circumstances of the suicide, stressors, and
current and past psychopathology; parents were also interviewed regarding
family history of psychopathology and availability of a firearm (Brent et al.,
1999). Like Kellerman and his colleagues, this research group found an
association between family gun ownership and the risk of suicide, with an
odds ratio of 3.0 (with a 95 percent confidence interval = 1.3-6.8) for older
adolescents and 7.3 (with a 95 percent confidence interval = 1.3-40.8) for
younger adolescents. They found that firearms in the home appeared to be a
stronger risk factor among subjects with no diagnosable psychiatric disorder.
The results that have been reported from these U.S. studies contrast
with a large case-control study from New Zealand, reported by Beautrais
and colleagues in 1996. This study compared a consecutive series of 197
persons of all ages who died by suicide, 302 individuals who made medically
serious but nonlethal suicide attempts, and 1,028 randomly selected
community controls. Suicide attempts by gunshot accounted for 13.3 percent
of suicides and only 1.3 percent of serious but nonlethal suicide attempts.
Access to a firearm was strongly associated with an increased risk
that gunshot would be chosen as the method of suicide or suicide attempt
(odds ratio = 107.9; 95 percent confidence interval 24.8 to 469.5), but this
access was associated with a much smaller, and statistically nonsignificant
increase in the overall risk of suicide (odds ratio = 1.4; 95 percent confidence
interval = 0.96 to 1.99).
How can one reconcile the very different estimates from the United
States and New Zealand? The Beautrais and Kellerman confidence intervals
do not overlap, but of course one interpretation of the overall literature is
that the estimate lies somewhere in the range between Beautrais, Brent, and
Kellerman, with possible differences in effect size by age group and country.
The U.S. and New Zealand studies together seem to suggest an odds ratio
that may be above one, but is not much larger than two, if one thinks effects
in the two countries are likely to be similar. However, the effects in the two
countries may differ for reasons that we do not yet understand.
One possibility is that the cultural correlates of gun ownership are
different in New Zealand and in the United States, and that, in one or both
countries, some of the association between household gun ownership and
the risk of suicide is explained by an unobserved characteristic of the families
or social networks of suicidal persons. This interpretation is supported
by two individual-level studies based on the National Longitudinal Study
on Adolescent Health (called AddHealth), which found that adolescents
who reported that they had access to a gun in their homes also reported
higher rates of nonlethal suicidal thoughts and behaviors (Resnick et al.,
1997; Borowsky, et al., 2001). These results may reflect reporting bias on
the part of the adolescents (if suicidal adolescents are more likely to admit,
or even brag about, the presence of a gun), familial transmission of a mood
disorder (if a single heritable trait increases the likelihood that a parent will
own a gun, and that an adolescent will experience suicidal thoughts), or
correlates of particular parenting styles or family constellations (if parents
who are more likely to own a gun are also more likely to have a distant or
rejecting relationship with an adolescent child). However, they indicate that
the association between household gun ownership and risk of suicide may
be due to factors beyond the relative lethality of firearms.