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Guns, Suicide, and Homicide: Individual-Level Versus Population-Level Studies

David Hemenway, PhD
[+] Article, Author, and Disclosure Information

From Harvard School of Public Health, Boston, Massachusetts.

Potential Conflicts of Interest: None disclosed. Forms can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M13-2657.

Requests for Single Reprints: David Hemenway, PhD, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115; e-mail, hemenway@hsph.harvard.edu.

Ann Intern Med. 2014;160(2):134-135. doi:10.7326/M13-2657
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This issue contains a systematic review and meta-analysis that finds that access to firearms is associated with risk for both completed suicide and being the victim of homicide. Although the results are consistent with previous literature reviews, the editorialist believes that this review provides a conservative estimate of the true relationship of guns to suicide and homicide at a societal level.

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Posted on January 28, 2014
Andrew Anglemyer, PhD, MPH
University of California San Francisco
Conflict of Interest: None Declared
In Dr Hemenway’s editorial, he correctly suggests our systematic review and meta-analysis (1) “provides too conservative an estimate of the relationship among guns and suicide and homicide at a societal level” (2). While we agree that our methods have likely underestimated the true relationship between guns and suicide or homicide victimization, we feel that our inclusion of only studies where the individual’s personal firearm experience was assessed does provide an estimate of the minimum likely risk.

The narrative around studies of firearms ownership and harms is usually around discrediting the causality assumptions, and causal inference is particularly problematic in ecologic studies. Critics are quick to point out conflicting “evidence” from various sources of rates and their interpretations. In fact, a commonly cited review of ecologic data by Kates and Mauser only adds fodder to the on-going debate (3). We purposefully excluded ecologic data, in part, to obviate this common critique regarding the interpretability of population-level data.

Dr Hemenway correctly points out that most individuals commit suicide with a firearm within their own home, thus potentially justifying using aggregate population-level data for suicide outcomes. Unfortunately, this would likely not be enough to convince doubters of the use of rate data to assert correlations between firearm access and suicide. More importantly, in our review we had two primary outcomes of interest-- suicide and homicide victimization. While we can make a reasonable assumption that the firearms used in the suicides were obtained from the home (albeit, still an assumption that we wanted to avoid), we cannot reasonably make that same assumption about the firearms used in homicides. In fact, even Dr Hemenway writes “most perpetrators [of homicides] do not use a gun from the victim’s home” (2). We feel that it would not have been prudent to use different inclusion criteria for different outcomes (i.e., include ecologic data for suicide outcomes and not for homicide outcomes) as the focus of our review was the access to firearms among cases, not among the perpetrators, and the result focuses on the home. Moreover, our results may help households understand what the risks are of keeping a firearm in their home, particularly if there is a household member who is depressed or if there is a violent relationship; results from ecologic studies may be better for evaluating policies.

Notwithstanding our review, ecologic studies are a good source of data for establishing trends and positing relationships. We agree that one potential future methodological review could compare the summary estimates we obtained from individual-level data with the summary estimates one would have obtained had ecologic data been included. Operationally, of course, there are a number of issues that a reviewer would need to consider: which rates of ownership to use (e.g., regional rates, state rates, city rates), which timeframe (i.e., most recent data, most reliable) and which types of suicide (i.e., include only firearm-related suicides or any suicides)? For these reasons, among others, ecologic data are seldom seen in meta-analyses of individual-level data. Assuming that the reviewer were able to overcome the operational obstacles of disparate rates over disparate regions describing dissimilar outcomes, he or she would have to ensure that the interpretation of the results from such a review are truly reflective of aggregated population-level data, and not reflective of individual-level data. Of course, there are conceptual steps to calculate ecologic relative risk (RR) estimates so that conclusions about individual-level behavior can be inferred, though there are inherent assumptions (4). The reviewer could pool these new “individual-level” RR estimates to get a pooled RR from ecologic studies.

To make comparisons between results from the meta-analysis of ecologic studies with the meta-analysis of the individual-level data we summarize, there are a number of approaches a reviewer could use. Namely, he or she could pool both results together to get a summary estimate from both ecologic and individual-level data, though combining estimates that were derived from different sources with different assumptions can be problematic. He or she could also perform a sensitivity analysis comparing the pooled estimates with and without ecologic data. Or he or she could perform a subgroup analysis comparing the pooled estimates from ecologic data and from individual-level data separately. We feel that there are indeed benefits from reviewing ecologic data, and Dr Hemenway’s suggestion for future research will compliment our current review nicely. The two reviews together could provide a more nuanced understanding of the true relationship between access to firearms and harms outcomes.


1. Anglemyer A, Horvath T, and Rutherford G. The Accessibility of Firearms and Risk for Suicide and Homicide Victimization Among Household Members. A Systematic Review and Meta-Analysis. Ann Intern Med 2014; 160: 101-10.
2. Hemenway D. Guns, Suicide, and Homicide: Individual-Level Versus Population-Level Studies. Ann Int Med 2014; 160: 134-135.
3. Kates D and Mauser G. Would Banning Firearms Reduce Murder and Suicide? A Review of International and Some Domestic Evidence. Harv J Law Public Policy 2007; 30 (2): 649-694.
4. Schuessler A. Ecological Inference. Proc Natl Acad Sci USA 1999; 96: 10578-10581.

Potential Politicization of the Gun Control Controversy
Posted on February 4, 2014
Robert B. Sklaroff, M.D.
Nazareth Hospital, Philadelphia PA
Conflict of Interest: None Declared

Because Public Health research predictably guides generation of Public Policy, it is necessary to scrutinize the political science underlying the paired gun-control review (1) and editorial (2); challenges are detected to fundamental standards that may compromise an otherwise sound meta-analysis of available literature. The last sentences of each are revelatory, for the former finds “restricting [access to a firearm in the home] may effectively prevent injury” and the latter concludes “obtaining a firearm not only endangers those living in the home, but also imposes substantial costs on the community.” Notwithstanding unaddressed Second Amendment constraints, the authors of both unabashedly campaign to restrict the right to bear arms, thereby ignoring—for example—the human compulsion to manifest reasonable self-defense.

The intuitive deduction, that availability of a firearm will increase the risk that momentary depression will yield suicide, is consistent with modern lay culture—recalling the 1945 movie “Spellbound”—and medical scholarship—recalling an essay published last year in this journal (3). Yet, it is undermined by the editorialist, who has argued that the widespread ownership of firearms in private hands in the U.S. promotes the spread of the "disease" of gun violence (4). He invoked a generalized reference to his book when claiming “There is no association between gun ownership levels and suicide by means other than guns. These studies have controlled for…depression [and] suicidal ideation.” If true, this assertion would undermine efforts to include scrutiny of mental health data during any mandated background-checks; alas, it is untrue, for a profile has been generated of psychiatric patients at high risk for suicide (5).

This latter citation was among the articles cited in the review (#26), prompting confusion when noting it was among three articles cited in the online Appendix—which purports to show “the disposition of studies excluded after full-text review”—along with two others (#32 and #60) “because the study populations were contained in previously published data included in this review.” Noting there are 59 published references and 97 online references, merely counting the number of citations associated with a particular reason for exclusion yields the observation that there is an admixture of articles that were included and articles that were excluded (i.e., some were among the first #1-59 and at least one was among the latter #60-97). The authors should have provided a cross-walk “pairing” of how one set of data was subsuming another set of myriad peer-reviewed studies, precluding concern that any undue selectivity existed.

Therefore, author-bias—seeking the ability to generate the above preordained outcome—could have clouded how subsidiary observations were drawn regarding, for example, the allegation of enhanced risk of being killed by a household member. And, overall, adopting a purely academic approach could have yielded insights, for example, as to the type of mental health diagnoses that might predispose to criminal gun-use; indeed, this entire body of work could then have been compared/contrasted with lethal violence committed via non-household, unregistered firearms, yielding far more useful insights as to what societal interventions might be optimal.

1. Andrew Anglemyer, Tara Horvath, George Rutherford; The Accessibility of Firearms and Risk for Suicide and Homicide Victimization Among Household Members - A Systematic Review and Meta-analysis. Ann. Intern. Med. 2014 Jan;160(2):101-110.
2. David Hemenway; Guns, Suicide, and Homicide: Individual-Level Versus Population-Level Studies. Ann. Intern. Med. 2014 Jan;160(2):134-135.
3. Carl E. Fisher, Jeffrey A. Lieberman; Getting the Facts Straight About Gun Violence and Mental Illness: Putting Compassion Before Fear. Ann. Intern. Med. 2013 Sep;159(6):423-424.
4. Wheeler, Timothy J. (September 2005). "Private Guns, Public Health". The Freeman. In http://en.wikipedia.org/wiki/Private_Guns,_Public_Health#cite_ref-free_1-0.
5. Brent DA, Perper JA, Moritz G, Baugher M, Schweers J, Roth C. Firearms and adolescent suicide. A community case-control study. Am J Dis Child. 1993; 147:1066-71.
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