Psychological Autopsy Studies

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.