Frequency of Improvised Explosive Devices and Suicide Attempts in the U.S. Army

MILITARY MEDICINE, 182, 3/4:e1697, 2017 Frequency of Improvised Explosive Devices and Suicide Attempts in the U.S. Army Robert J. Ursano, MD*; Ronald C. Kessler, PhD ; James A. Naifeh, PhD*; Holly Herberman Mash, PhD*; Carol S. Fullerton, PhD*; Paul D. Bliese, PhD ; LTC Gary H. Wynn, MC USA*; Pablo A. Aliaga, MA*; Christina Wryter, BA*; Nancy A. Sampson, BA ; Tzu-Cheg Kao, PhD ; Lisa J. Colpe, PhD, MPH ; Michael Schoenbaum, PhD ; Kenneth L. Cox, MD, MPH**; Steven G. Heeringa, PhD ; Murray B. Stein, MD, MPH ; On behalf of the Army STARRS collaborators ABSTRACT Background: Improvised explosive devices (IEDs) were a prominent and initially new threat in the Iraq and Afghanistan war which raised concerns and anticipatory fear in and out of theater. This study examined the association of monthly IED rates with risk of soldier suicide attempt among those deployed and nondeployed. Methods: Personmonth records for all active duty Regular Army suicide attempters from 2004 through 2009 (n = 9,791) and an equal-probability sample of control person-months (n = 183,826) were identified. Logistic regression analyses examined soldiers risk of attempting suicide as a function of monthly IED frequency, controlling for sociodemographics, servicerelated characteristics, rate of deployment/redeployment, and combat deaths and injuries. The association of IED frequency with suicide attempt was examined overall and by time in service and deployment status. Findings: Soldiers risk of suicide attempt increased with increasing numbers of IEDs. Suicide attempt was 26% more likely for each 1,000 IED increase in monthly frequency (odds ratio [OR] = 1.26, 95% confidence interval [CI] = 1.22 1.30). The association of IED frequency with suicide attempt was greater for soldiers in their first 2 years of service (OR = 1.30, 95% CI = 1.25 1.36) than for those with 3 or more years of service (OR = 1.18, 95% CI = 1.12 1.24). Among soldiers in their first 2 years of service, the association was constant, regardless of deployment status (χ 2 2 =3.89,p=0.14). Among soldiers with 3 or more years of service, the association was higher for those never deployed (OR = 1.12, 95% CI = 1.01 1.24) and currently deployed (OR = 1.14, 95% CI = 1.05 1.23) than for those previously deployed. Discussion: To our knowledge, this is the first study to examine and demonstrate an association between the aggregate frequency of IEDs and risk of suicide attempts among U.S. Army soldiers. This association was observed across deployment status and time in service, and for early-career soldiers in particular. The findings suggest that the threat of new weapons may increase stress burden among soldiers. Targeting risk perception and perceived preparedness, particularly early in a soldier s career, may improve psychological resilience and reduce suicide risk. INTRODUCTION Improvised explosive devices (IEDs) were a prominent and initially new threat in the Iraq and Afghanistan war, 1 where they were responsible for more than half of U.S. military combat casualties. 2 Their use reached unprecedented frequency, increasing steadily from the onset of combat operations in 2001 to a peak of 2,612 IED incidents (exploded, detected, or defused) in March 2007 and the highest number of IEDrelated casualties (n = 655) in June of 2007. 3,4 IEDs are characterized by unpredictability, increasing the uncertainty of one s safety. In addition, early on in the war they were especially unfamiliar weapons. Such experiences can affect service members perceptions of threat, safety, and vulnerability, and increase overall operational stress burden. 5,6 Suicide attempts, which also rose sharply during the same time period, 7 are one indicator of psychological distress in soldiers. The association between the psychological impact IEDs among those deployed and not deployed and U.S. Army suicide attempts has not been studied. Risk of attempting suicide during the wars in Iraq and Afghanistan was highest among soldiers in their first 2 years of service, and among soldiers who were never deployed or previously deployed compared to currently deployed. 8 The elevated risk among those still in training and those who had never deployed indicates *Department of Psychiatry, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814. Department of Health Care Policy, Harvard Medical School, 180A Longwood Avenue, Boston, MA 02115. Darla School of Business, University of South Carolina, 1014 Greene Street, Columbia, SC 29208. Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge road, Bethesda, MD 20814. National Institute of Mental Health, 6001 Executive Boulevard, Rockville, MD 20852. U.S. Army Public Health Command, Army Public Health Center, 5158 Blackhawk Road, Aberdeen Proving Ground, MD 21010. **University of Michigan, Institute for Social Research, 426 Thompson Street, Ann Arbor, MI 48104. Department of Psychiatry and Department of Family Medicine and Public Health, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093. VA San Diego Healthcare System, 3350 La Jolla Village Drive, La Jolla, CA 92161. The contents are solely the responsibility of the authors and do not necessarily represent the views of the Department of Health and Human Services, NIMH, the Department of the Army, the Department of Defense, the Uniformed Services University of the Health Sciences, or the Center for the Study of Traumatic Stress. doi: 10.7205/MILMED-D-16-00270 e1697

that direct exposure to combat and other war zone stressors was not the sole factor influencing the suicide attempt rate and highlights the importance of examining other factors. Both direct exposure to IEDs and concerns about IED threat have been associated with elevated risk for post-traumatic stress disorder among military personnel serving in Afghanistan. 9 The influence of IED-related concerns raises the possibility that increases in IED frequency may adversely affect the mental and behavioral health of soldiers who are not in-theater. Concerns about the threat of IEDs may be further compounded by inexperience. Soldiers returning from their first peacekeeping deployment reported greater distress than those who had participated in other peacekeeping operations. 10 We examined the association of IED frequency and suicide attempts in soldiers in the U.S. Army between 2004 and 2009 after controlling for sociodemographics, service-related characteristics, and indicators of war/operational intensity, including combat deaths and injuries, and deployment into and out of the theater of the war. 8,11 We hypothesized that the influence of IEDs would be modified by deployment status and years of experience in the Army. METHOD Sample The Historical Administrative Data Study (HADS) is a component of the Army STARRS database. Creation and analysis of the Army STARRS consolidated and deidentified database were approved by the Institutional Review Boards of the Uniformed Services University of the Health Sciences for the Henry M. Jackson Foundation (the primary grantee), the University of Michigan Institute for Social Research (site of the Army STARRS Data Enclave), University of California, San Diego, and Harvard Medical School. The HADS includes individual-level person-month records for all soldiers on active duty between January 1, 2004, and December 31, 2009 (n = 1.66 million). 12 In this longitudinal, retrospective cohort study, we focused on records for the 975,057 Regular Army soldiers on active duty during this time (excluding activated Army National Guard and Army Reserve), 9,791 of whom had a documented suicide attempt. Data were analyzed using a discrete-time survival framework with person-month as the unit of analysis, 13,14 We reduced computational intensity by selecting from the population an equal-probability 1:200 sample of control person-months stratified by gender, rank, time in service, deployment status (never, currently, previously), and historical time (n = 183,826 person-month records). Measures Suicide Attempts Soldiers who attempted suicide were identified using Army/ Department of Defense (DoD) administrative records from the Department of Defense Suicide Event Report (DoDSER), 15 a DoD-wide surveillance mechanism that aggregates information on suicidal behaviors via a standardized form completed by medical providers at DoD treatment facilities, and International Classification of Diseases, 9th Revision, Clinical Modification diagnostic codes E950-E958 (indicating selfinflicted poisoning or injury with suicidal intent) from health care encounter information for military and civilian treatment facilities, combat operations, and aeromedical evacuations. 16 For soldiers with multiple suicide attempts, we selected the first attempt using a hierarchical classification scheme that prioritized Do DSER records on the basis of that system s more extensive reporting requirements. 7 Sociodemographic and Service-Related Characteristics Army and DoD personnel records were used to construct sociodemographic variables, including gender, current age, race/ethnicity (White, Black, Hispanic, Asian/other), education (less than high school, high school, at least some college), and marital status (never, currently, or previously married), and service-related variables, including rank (enlisted, officer), time in Army service, and deployment status (never, currently, or previously deployed). Combat Operational Variables IEDs. Monthly frequency of IEDs in Iraq and Afghanistan was determined using data provided by the Joint IED Defeat Organization (www.jieddo.mil). The count included effective and ineffective IED incidents (Fig. 1). Monthly frequency of IEDs was scaled in multiples of 1,000 (1 = 1,000 IED events). Combat deaths and injuries. Monthly frequency of U.S. Army combat deaths and injuries were identified using data from the Defense Casualty Analysis System (www.dmdc.osd.mil) (Fig. 1). The count included deaths and all wounds and other injuries incurred in action. Monthly frequency of combat deaths and injuries was scaled in multiples of 100 (1 = 100 combat deaths and injuries). Soldiers deployed and redeployed. Monthly frequencies of soldiers deployed and redeployed were calculated using data from Army/DoD administrative personnel records available in the HADS. We calculated the number of active duty Regular Army soldiers deployed to the Iraq or Afghanistan operational theater each calendar month (deployment), and the number of soldiers who returned each calendar month (redeployment). Monthly frequencies were scaled in multiples of 100,000 (1 = 100,000 soldiers deployed/redeployed). Statistical Analysis All analyses were conducted using SAS Version 9.3 (SAS Institute Inc., Cary, NC, 2011). Univariate logistic regression analyses were conducted to examine the independent associations of (a) monthly IED frequency, (b) monthly frequency of combat deaths and injuries, and (c) monthly frequency of deployment/redeployment with risk of suicide attempts. Multivariate logistic regression analyses were then conducted to e1698

FIGURE 1. Monthly frequency of IED incidents and combat deaths and injuries, 2004 2009. IED incidents include effective and ineffective IED incidents targeting coalition forces, effective IED incidents targeting Iraq Security Forces, and IEDs that were found and cleared. Combat deaths include hostile in action deaths. Combat injuries include all hostile and nonhostile wounds and injuries incurred in action. examine the association of monthly IED frequency with suicide attempts, adjusting for monthly frequency of combat deaths and injuries, monthly frequency of deployment and redeployment, as well as for individual differences in sociodemographics (gender, current age, race/ethnicity, education, marital status) and service-related variables (rank, time in service, deployment status). We examined variation in the association between IED frequency and suicide attempts as a function of time in service and deployment status. All multivariate models included a dichotomous indicator corresponding to increasing (January 2004 through May 2007) versus decreasing (June 2007 through December 2009) IED incidents. The peak of casualties (troops killed or wounded in action) occurred in June 2007, with a marked reduction in IED incidents following that period. 3,4,17 Logistic regression coefficients were exponentiated to obtain odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS The majority of the sample was male (86.02%), enlisted (83.52%), 29 years old or younger (62.14%), White (62.03%), high school educated (64.89%), and currently married (57.43%). Three-quarters of soldiers (74.94%) had 3 or more years of Army service and 40.02% had never deployed (Table I). Monthly IED frequency (scaled per 1,000) ranged from 0.51 to 3.89 (M = 1.91, SD = 0.88). Monthly frequency of combat deaths and injuries (scaled per 100) ranged from 0.83 to 8.11 (M = 3.69, SD = 1.72). Active duty Regular Army soldiers deployed per month (scaled per 100,000) ranged from 0.42 to 3.97 (M = 1.65, SD = 0.68), and soldiers redeployed per month (scaled per 100,000) ranged from 0.54 to 4.33 (M = 1.59, SD = 0.79) (Table II). In univariate analyses, the odds of suicide attempts were significantly associated with the frequency of IEDs (χ 2 1 = 150.32, p < 0.0001), combat deaths and injuries (χ 2 1 = 13.01, p = 0.0003), number of soldiers deployed (χ 2 1 = 14.87, p < 0.0001), and number of soldiers redeployed (χ 2 1 = 37.82, p < 0.0001). Odds of a suicide attempt increased with IED frequency (OR = 1.15, 95% CI = 1.12 1.17) but decreased with measures of operational activity, including frequency of combat deaths and injuries (OR = 0.98, 95% CI = 0.97 0.99), number of soldiers deployed (OR = 0.94, 95% CI = 0.92 0.97), and redeployed (OR = 0.92, 95% CI = 0.90 0.95) (Table III). IED frequency (OR = 1.26, 95% CI = 1.22 1.30) and combat deaths and injuries (OR = 0.94, 95% CI = 0.92 0.96) both remained associated with suicide attempts after adjusting for sociodemographic, service-related, and combat operational e1699

TABLE I. Sociodemographic and Service-Related Characteristics Among Active Duty Regular Army Soldiers, 2004 2009 a Demographic Characteristics Weighted Proportion (%) Unweighted Person-Months (N = 193,617) Weighted Person-Months (N = 36,774,991) Gender Male 86.02 165,444 31,635,503 Female 13.98 28,173 5,139,488 Current Age <21 years 12.58 26,428 4,625,915 21 24 26.63 52,468 9,793,717 25 29 22.93 43,950 8,432,994 30 34 14.94 28,135 5,494,267 35 39 12.47 23,251 4,584,132 40+ 10.45 19,385 3,843,966 Race White 62.03 120,916 22,809,901 Black 21.13 40,289 7,772,235 Hispanic 10.62 20,511 3,905,190 Asian/Other 6.22 11,901 2,287,665 Education <High School b 10.81 22,761 3,976,692 High School 64.89 125,675 23,864,584 Some College/College+ 24.29 35,181 8,933,715 Marital Status Never Married 38.31 75,918 14,090,294 Currently Married 57.43 109,640 21,121,055 Previously Married 4.25 8,059 1,563,642 Service-Related Characteristics Rank Enlisted 83.52 163,178 30,715,250 Officer 16.48 30,439 6,059,741 Time in Service First 2 Years of Service 25.06 51,495 9,215,445 3 or More Years of Service 74.94 142,122 27,559,546 Deployment Status Never Deployed 40.02 42,671 8,342,762 Currently Deployed 22.69 79,502 14,715,156 Previously Deployed 37.30 71,444 13,717,073 Suicide Attempt Yes 0.03 9,791 9,791 No 99.97 183,826 36,765,200 a The sample of soldiers (n = 9,791 cases, 183,826 control person-months) from the Army STARRS HADS includes all active duty Regular Army soldiers (i.e., excluding those in the U.S. Army National Guard and Army Reserve) with a suicide attempt in their administrative records during the years 2004 2009, plus a 1:200 stratified probability sample of all other active duty Regular Army person-months in the population exclusive of soldiers with a suicide attempt or other nonfatal suicidal event (e.g., suicidal ideation) and person-months associated with death (i.e., suicides, combat deaths, homicides, and deaths resulting from other injuries or illnesses). All records in the 1:200 sample were assigned a weight of 200 to adjust for the undersampling of months not associated with suicide attempt. b <High School includes General Educational Development credential, home study diploma, occupational program certificate, correspondence school diploma, high school certificate of attendance, adult education diploma, and other nontraditional high school credentials. variables, whereas monthly number of soldiers deployed (χ 2 1 = 1.37, p = 0.24) and redeployed (χ 2 1 = 3.51, p = 0.06) were no longer significant (Table III). In a multivariate model that adjusted for sociodemographics, service-related variables, and combat operational variables, there was a significant interaction of IED frequency by time in service (first 2 years, 3 or more years [including soldiers in their third year]) (χ 2 1 =50.80,p < 0.0001). Stratifying by time in service, IED frequency was associated with higher odds of suicide attempt among soldiers in their first 2 years of service (OR = 1.30, 95% CI = 1.25 1.36) than among those with 3 or more years of service (OR = 1.18, 95% CI = 1.12 1.24). To examine whether the weaker association among soldiers with 3 or more years of service was the result of selection bias (i.e., healthier soldiers choosing, and being permitted, to re-enlist after their first 4-year tour), we also conducted these analyses with time in service divided into three groups (first 2 years, 3 4 years, 5 or more years). The interaction of IED frequency with this modified time in service variable remained significant (χ 2 2 =50.3,p < 0.0001). Stratifying by time in service, IED frequency was associated with lower odds among soldiers with 3 to 4 years of service (OR = 0.85, 95% CI = 0.80 0.90) or 5 or more years of service (OR = 0.85, 95% CI = 0.80 0.90) than among those in their first 2 years. There was no e1700

TABLE II. Combat Operational Variables During the Wars in Iraq and Afghanistan, 2004 2009 Actual Scaled a Combat Operational Variables Mean SD Mean SD IED Incidents per Month 1,913.83 880.29 1.91 0.88 Combat Deaths and 368.60 172.49 3.69 1.72 Injuries per Month Soldiers Deployed 16,491.49 6,851.91 1.65 0.68 per Month b Soldiers Redeployed per Month b 15,946.20 7,939.64 1.59 0.79 a IED incidents scaled in multiples of 1,000; combat deaths and injuries scaled in multiples of 100; soldiers deployed and redeployed scaled in multiples of 100,000. b Based on active duty Regular Army soldiers (i.e., excluding Army National Guard and Army Reserve). difference between 3 to 4 years and 5 or more years (OR = 0.99, 95% CI = 0.93 1.07), suggesting that selection bias related to re-enlistment did not account for the differential effects of IED frequency by time in service. Consequently, we continued to use the dichotomous indicator of time in service (first 2 years, 3 or more years) in subsequent analyses. We next examined the interaction of IED frequency with deployment status (never, current, previously deployed) in groups stratified by time in service (first 2 years, 3 or more years) (Table IV). The interaction was not significant among soldiers in their first 2 years of service (χ 2 2 =3.89, p=0.14), indicating that for this group, the effect of IED frequency did not differ by deployment status. However, among those with 3 or more years of service, the interaction was significant (χ 2 2 =8.85, p = 0.012). Pairwise analyses (not shown in Table IV) indicated higher odds among never (OR = 1.12, 95% CI = 1.03 1.21]) and currently (OR = 1.11, 95% CI = 1.01 1.24) deployed soldiers than among those previously deployed, and no difference between soldiers who were never or currently deployed (Table IV). Given the finding of a negative association of combat deaths and injuries with suicide attempts, we further investigated the association of combat deaths and injuries to suicide attempts in a similar manner. After adjusting for sociodemographics, service-related variables, and combat operational variables, there was a significant interaction of combat deaths and injuries by time in service (first 2 years, 3 or more years) (χ 2 1 = 66.7, p < 0.00001). Stratifying by time in service revealed that, although increased combat deaths and injuries were associated with lower risk of suicide attempts in both time in service groups, there was an even slightly lower risk in those with 3 or more years of service (OR = 0.93, 95% CI = 0.91 0.96) compared to soldiers in their first 2 years of service (OR = 0.95, 95% CI = 0.93 0.97), indicating a significant but modest effect. Within groups stratified by time in service, the interaction of combat deaths and injuries by deployment status was not significant among soldiers in their first 2 years of service (χ 2 2 =0.28,p=0.87) or 3 or more years of service (χ 2 2 =2.43, p=0.30), indicating that the effect of combat deaths and injuries did not differ by deployment status in either group. DISCUSSION Monthly IED frequency during the wars in Iraq and Afghanistan was positively associated with suicide attempts among deployed, previously deployed, and never deployed U.S. Army soldiers, with the overall risk increasing approximately 30% for every 1,000 additional IED incidents in a given month. This association was stronger among soldiers in their first 2 years of service. For this group of less experienced soldiers, this association was the same regardless of deployment status. However, for more experienced soldiers, the association of IED frequency and suicide attempt risk was greater among those never and currently deployed, perhaps reflecting the contribution of anticipatory anxiety and fear, or other differences in training and occupational variables that emerge in this TABLE III. Univariate and Multivariate Associations of IED Frequency and Other Combat Operational Variables with Suicide Attempts among Active Duty Regular Army Soldiers a Univariate Models Multivariate Model c Combat Operational Variables b OR 95% CI χ 2 1 OR 95% CI χ 2 1 IED Frequency per Month 1.15 1.12 1.17 150.32**** 1.26 1.22 1.30 202.56**** Combat Deaths and Injuries per Month 0.98 0.97 0.99 13.01*** 0.94 0.92 0.96 54.94**** Soldiers Deployed per Month 4 0.94 0.92 0.97 14.87**** 0.98 0.95 1.01 1.37 Soldiers Redeployed per Month d 0.92 0.90 0.95 37.82**** 0.97 0.95 1.00 3.51 a The sample of soldiers (n = 9,791 cases, 183,826 control person-months) from the Army STARRS HADS includes all active duty Regular Army soldiers (i.e., excluding those in the U.S. Army National Guard and Army Reserve) with a suicide attempt in their administrative records during the years 2004 2009, plus a 1:200 stratified probability sample of all other active duty Regular Army person-months in the population exclusive of soldiers with a suicide attempt or other nonfatal suicidal event (e.g., suicidal ideation) and person-months associated with death (i.e., suicides, combat deaths, homicides, and deaths resulting from other injuries or illnesses). All records in the 1:200 sample were assigned a weight of 200 to adjust for the under-sampling of months not associated with suicide attempt. b IED frequency scaled in multiples of 1,000; combat deaths and injuries scaled in multiples of 100; soldiers deployed and redeployed scaled in multiples of 100,000. c The multivariate model included sociodemographic variables (gender, current age, race, education, marital status), service-related variables (rank, time in service, deployment status), historical time (January 2004 to May 2007 vs. June 2007 to December 2009), and combat operational variables (IED frequency [scaled in multiples of 1,000], combat deaths and injuries [scaled in multiples of 100], soldiers deployed and redeployed [scaled in multiples of 100,000]). d Based on active duty Regular Army soldiers (i.e., excluding Army National Guard and Army Reserve). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. e1701

TABLE IV. Multivariate Associations of IED Frequency With Suicide Attempt by Time In Service And Deployment Status Among Active Duty Regular Army Soldiers a,b Effect of IED Frequency (per 1,000 Incidents) First 2 Years of Service 3 or More Years of Service OR 95% CI OR 95% CI χ 2 1 Total 1.30**** 1.25 1.36 1.18**** 1.12 1.24 50.80**** Never Deployed 1.32**** 1.20 1.44 Currently Deployed 1.18* 1.03 1.36 Previously Deployed 1.11** 1.04 1.19 χ 2 2 3.89 8.85* a The sample of soldiers (n = 9,791 cases, 183,826 control person-months) from the Army STARRS HADS includes all active duty Regular Army soldiers (i.e., excluding those in the U.S. Army National Guard and Army Reserve) with a suicide attempt in their administrative records during the years 2004 2009, plus a 1:200 stratified probability sample of all other active duty Regular Army person-months in the population exclusive of soldiers with a suicide attempt or other nonfatal suicidal event (e.g., suicidal ideation) and person-months associated with death (i.e., suicides, combat deaths, homicides, and deaths resulting from other injuries or illnesses). All records in the 1:200 sample were assigned a weight of 200 to adjust for the under-sampling of months not associated with suicide attempt. b The OR in each cell is the result of a separate logistic regression model examining the effect of IED frequency, adjusting for sociodemographic and service-related variables (gender, current age, race education, marital status, rank), historical time (January 2004 to May 2007 vs. June 2007 to December 2009), and combat operational variables (IED frequency [scaled in multiples of 1,000], combat deaths and injuries [scaled in multiples of 100], soldiers deployed and redeployed [scaled in multiples of 100,000]). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. group with greater experience. Importantly, these associations persisted after adjusting for measures of operational activity (i.e., combat death and injuries, and the number of soldiers deployed and redeployed each month). The contribution of IED frequency to risk of suicide attempt is consistent with theoretical and empirical work suggesting that novel, uncontrollable threats increase fear and distress, 5,6 and that this effect is further compounded by less experience. The finding that the association was not as strong among those with greater experience is in accordance with the concept of stress inoculation, 18 which suggests that previous exposure and experience can reduce anxiety and improve performance. 19 More experienced soldiers may have more training, preparedness, and social context for interpreting and ameliorating the stress of the IED threat. The finding that IED frequency was associated with elevated risk among previously deployed soldiers suggests that these soldiers continue to be affected by learning about IED-related incidents, which are then part of their personal experience, even after leaving the deployed setting. Future studies may examine the types and patterns of communication and social connectedness that may carry the stress of IED-related incidents and differences in the perceptions of threat among soldiers before, during, and after deployment. Importantly, exposure to media coverage of traumatic events has been associated with perceived threat, vulnerability and post-traumatic stress symptoms, 20 22 particularly for those who may already be at risk for developing symptoms as a result of prior trauma history or psychopathology. 23 Future studies should consider the role of individual and group differences that may amplify or reduce cognitive and behavioral responses to IEDs. For example, individual variation in attentional bias to threat, assessed during military recruitment and before deployment, was found to predict postdeployment post-traumatic stress disorder symptoms. 24 The degree to which soldiers experience emotional connections with IED-related casualties may also be important. Such emotional connectedness has been found to increase risk of distress, post-traumatic stress symptoms, and somatic complaints in disaster workers and those responsible for body recovery following natural and human-made disasters. 25 28 This may be particularly important for previously deployed soldiers who may be more likely to identify with currently deployed soldiers who are still in harm s way. Although not the primary focus of this study, it is noteworthy that increased frequency of combat deaths and injuries was associated with a lower likelihood of soldiers attempting suicide, warranting further study. This finding is similar to reports of a decrease in suicides among soldiers during World War I and World War II as compared to peacetime rates. 29,30 This study has several limitations. First, we examined population-level IED data, which does not contain personlevel information on IED exposure. As a result, we were unable to assess the risk of suicide attempt associated with personally experiencing an IED incident. This is an important question for future studies to address. Second, although we adjusted for the monthly frequency of combat deaths and injuries, we cannot rule out the possibility that our IED variable is a proxy for enemy attacks or other threat related events. Third, the suicide attempt data were from administrative and medical records, and are therefore recognized suicide attempts, although perhaps also therefore including the most severe. These records may be subject to errors in clinician diagnosis or medical coding. Fourth, as these data focus exclusively on the 2004 2009 period, our findings may not generalize to earlier and later periods of the wars in Iraq and e1702

Afghanistan, or to other U.S. military conflicts. Fifth, although we controlled for indicators of war/operational activity, there may be additional important indicators that should be considered. Sixth, we focused on a limited set of important individual characteristics (sociodemographic and service-related variables). Seventh, the observed differences across deployment status and time in service are not evidence of withinperson changes in suicide attempt risk over time, as the composition of these groups is affected by the nonrandom nature of both deployment and Army attrition. 31 To our knowledge, this is the first study to examine and demonstrate an aggregate association between the frequency of IEDs and risk of suicide attempts among U.S. Army soldiers. The finding that the association was positive across deployment status and for all career service lengths, and particularly for early-career soldiers suggests that targeting risk perception is important and particularly so early in a soldier s career. Given evidence that perceived preparedness for deployment is associated with more positive mental health outcomes, 32 34 including enhanced training in how to prepare for and manage distress related to IEDs may improve psychological resilience and reduce suicide risk. ACKNOWLEDGMENTS Army STARRS was sponsored by the Department of the Army and funded under co-operative agreement number U01MH087981 with the U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Mental Health (NIH/NIMH). The Army STARRS Team consists of Co-Principal Investigators: Robert J. Ursano, MD (Uniformed Services University of the Health Sciences) and Murray B. Stein, MD, MPH (University of California San Diego and VA San Diego Healthcare System); Site Principal Investigators: Steven Heeringa, PhD (University of Michigan) and Ronald C. Kessler, PhD (Harvard Medical School); National Institute of Mental Health (NIMH) collaborating scientists: Lisa J. Colpe, PhD, MPH, and Michael Schoenbaum, PhD; Army liaisons/ consultants: COL Steven Cersovsky, MD, MPH (USAPHC) and Kenneth Cox, MD, MPH (USAPHC); Other team members: Pablo A. Aliaga, MA (Uniformed Services University of the Health Sciences); COL David M. Benedek, MD (Uniformed Services University of the Health Sciences); K. Nikki Benevides, MA (Uniformed Services University of the Health Sciences); Paul D. Bliese, PhD (University of South Carolina); Susan Borja, PhD (NIMH); Evelyn J. Bromet, PhD (Stony Brook University School of Medicine); Gregory G. Brown, PhD (University of California San Diego); Christina L. Wryter, BA (Uniformed Services University of the Health Sciences); Laura Campbell-Sills, PhD (University of California San Diego); Catherine L. Dempsey, PhD, MPH (Uniformed Services University of the Health Sciences); Carol S. Fullerton, PhD (Uniformed Services University of the Health Sciences); Nancy Gebler, MA (University of Michigan); Robert K. Gifford, PhD (Uniformed Services University of the Health Sciences); Stephen E. Gilman, ScD (Harvard School of Public Health); Marjan G. Holloway, PhD (Uniformed Services University of the Health Sciences); Paul E. Hurwitz, MPH (Uniformed Services University of the Health Sciences); Sonia Jain, PhD (University of California San Diego); Tzu-Cheg Kao, PhD (Uniformed Services University of the Health Sciences); Karestan C. Koenen, PhD (Columbia University); Lisa Lewandowski-Romps, PhD (University of Michigan); Holly Herberman Mash, PhD (Uniformed Services University of the Health Sciences); James E. McCarroll, PhD, MPH (Uniformed Services University of the Health Sciences); James A. Naifeh, PhD (Uniformed Services University of the Health Sciences); Tsz Hin Hinz Ng, MPH (Uniformed Services University of the Health Sciences); Matthew K. Nock, PhD (Harvard University); Rema Raman, PhD (University of California San Diego); Holly J. Ramsawh, PhD (Uniformed Services University of the Health Sciences); Anthony Joseph Rosellini, PhD (Harvard Medical School); Nancy A. Sampson, BA (Harvard Medical School); LCDR Patcho Santiago, MD, MPH (Uniformed Services University of the Health Sciences); Michaelle Scanlon, MBA (NIMH); Jordan W. Smoller, MD, ScD (Harvard Medical School); Amy Street, PhD (Boston University School of Medicine); Michael L. Thomas, PhD (University of California San Diego); Patti L. Vegella, MS, MA (Uniformed Services University of the Health Sciences); Leming Wang, MS (Uniformed Services University of the Health Sciences); Christina L. 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