Survey response over 15 years of follow-up in the Millennium Cohort Study.

BACKGROUND: Patterns of survey response and the characteristics associated with response over time in longitudinal studies are important to discern for the development of tailored retention efforts aimed at minimizing response bias. The Millennium Cohort Study, the largest and longest running cohort study of military personnel and veterans, is designed to examine the long-term health effects of military service and experiences and thus relies on continued participant survey responses over time. Here, we describe the response rates for follow-up survey data collected over 15 years and identify characteristics associated with follow-up survey response and mode of response (paper vs. web). METHOD: Patterns of follow-up survey response and response mode (web, paper, none) were examined among eligible participants (n=198,833), who were initially recruited in four panels from 2001 to 2013 in the Millennium Cohort Study, for a follow-up period of 3-15 years (2004-2016). Military and sociodemographic factors (i.e., enrollment panel, sex, birth year, race and ethnicity, educational attainment, marital status, service component, service branch, pay grade, military occupation, length of service, and time deployed), life experiences and health-related factors (i.e., military deployment/combat experience, life stressors, mental health, physical health, and unhealthy behaviors) were used to examine follow-up response and survey mode over time in multivariable generalized estimating equation models. RESULTS: Overall, an average response rate of 60% was observed across all follow-up waves. Factors associated with follow-up survey response over time included increased educational attainment, married status, female sex, older age, military deployment (regardless of combat experience), and higher number of life stressors, mental health issues, and physical health diagnoses. CONCLUSION: Despite the challenges associated with collecting multiple waves of follow-up survey data from members of the U.S. military during and after service, the Millennium Cohort Study has maintained a relatively robust response rate over time. The incorporation of tailored messages and outreach to those groups least likely to respond over time may improve retention and thereby increase the representativeness and generalizability of collected survey data.

The Millennium Cohort Study: The first 20 years of research dedicated to understanding the long-term health of US Service Members and Veterans.

PURPOSE: The Millennium Cohort Study, the US Department of Defense's largest and longest running study, was conceived in 1999 to investigate the effects of military service on service member health and well-being by prospectively following active duty, Reserve, and National Guard personnel from all branches during and following military service. In commemoration of the Study's 20th anniversary, this paper provides a summary of its methods, key findings, and future directions. METHODS: Recruitment and enrollment of the first 5 panels occurred between 2001 and 2021. After completing a baseline survey, participants are requested to complete follow-up surveys every 3-5 years. RESULTS: Study research projects are categorized into 3 core portfolio areas (psychological health, physical health, and health-related behaviors) and several cross-cutting areas and have culminated in more than 120 publications to date. For example, some key Study findings include that specific military service-related factors (e.g., experiencing combat, serving in certain occupational subgroups) were associated with adverse health-related outcomes and that unhealthy behaviors and mental health issues may increase following the transition from military service to veteran status. CONCLUSIONS: The Study will continue to foster stakeholder relationships such that research findings inform and guide policy initiatives and health promotion efforts.

Cigarette smoking patterns among U.S. military service members before and after separation from the military.

U.S. military Service members have consistently smoked more than the general population and the prevalence of smoking is even higher among U.S. veterans. Our study examined cigarette smoking patterns among Service members before and after military separation to better understand the disproportionate rate of smoking among veterans. Data from the Millennium Cohort Study were used. All study participants were in the military at baseline and some transitioned from the military to civilian life during the observation period. We investigated any impact of military separation on smoking, as well as other potential risk factors for smoking. Overall, we observed higher smoking prevalence among veterans than Service members. Additionally, we found that Service members smoked more while approaching their separation from the military. Longitudinal analysis revealed military separation was not a risk factor for smoking, as we had hypothesized. Baseline smoking was the most influential predictor of current smoking status. Other significant factors included alcohol consumption, life stressors, and mental health conditions, among others. Military separation was not a risk factor for smoking. However, Service members in the process of transitioning out of the military, as well as high alcohol consumers and Service members with mental health conditions, may be at higher risk of smoking. Including smoking prevention/cessation programs in pre-separation counseling sessions and developing smoking screening and cessation programs targeting specific high-risk subgroups may reduce smoking among Service members and veterans.

Comparison of Posttraumatic Stress Disorder Checklist Instruments From Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition vs Fifth Edition in a Large Cohort of US Military Service Members and Veterans.

Importance: The definition of posttraumatic stress disorder (PTSD) changed markedly between the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) and DSM-5, creating challenges for studies and in medical settings spanning this transition. Objective: To evaluate the ability to compare and assess PTSD, based on DSM-IV and DSM-5 criteria, using PTSD Checklists (PCLs). Design, Setting, and Participants: This diagnostic study was conducted with survey data collected in October 2019, from the Millennium Cohort Study, a population-based US military cohort study. The population for the present study was restricted to a subset of initial web responders of the 2019 survey cycle, randomly assigned to 1 of 4 survey groups. Exposures: Each group received the DSM-IV and DSM-5 PCL (PCL-Civilian [PCL-C] version and PCL for DSM-5 [PCL-5]). PCL instruments were counterbalanced to control for order effects. Main Outcomes and Measures: Survey data were used to assess PTSD (using the PCL-C and PCL-5), major depressive disorder (using the Patient Health Questionnaire), generalized anxiety (using the Generalized Anxiety Disorder scale), and problem drinking (using the Patient Health Questionnaire). Demographic and military characteristics included age, sex, race/ethnicity, marital status, education, service branch, pay grade, enrollment panel, and military service status. Results: Among the 1921 participants (mean [SD] age, 50.1 [12.5] years), 1358 (70.7%) were men, 1638 (85.3%) were non-Hispanic White individuals, 1440 (75.0%) were married, and 1190 (61.9%) had at least a bachelor's degree; 295 (15.4%) had probable PTSD according to DSM-IV criteria with PCL-C compared with 286 (14.9%) using DSM-5 criteria with PCL-5 (κ = 0.77). There was substantial agreement between PCLs for probable PTSD based on DSM-IV criteria (295 [15.4%] with PCL-C; 316 [16.4%] with PCL-5; κ = 0.80) and DSM-5 criteria (286 [14.9%] with PCL-5; 258 [13.4%] with PCL-C; κ = 0.77). Estimated PTSD sum scores showed excellent agreement with observed scores. Using an established crosswalk, PCL-5 sum scores estimated with the PCL-C were similar to observed PCL-5 scores. Of the 17 corresponding items between the 2 instruments, 16 had substantial agreement. Appending 2 additional PCL-C items to the PCL-5 did not significantly alter estimates. The PCL-C and PCL-5 had nearly identical associations with comorbid conditions. Conclusions and Relevance: The findings of this diagnostic study suggest that PTSD can be successfully assessed and compared over time with either PCL instrument in veteran and military populations.

Association of Combat Experiences With Suicide Attempts Among Active-Duty US Service Members.

Importance: There is uncertainty about the role that military deployment experiences play in suicide-related outcomes. Most previous research has defined combat experiences broadly, and a limited number of cross-sectional studies have examined the association between specific combat exposure (eg, killing) and suicide-related outcomes. Objective: To prospectively examine combat exposures associated with suicide attempts among active-duty US service members while accounting for demographic, military-specific, and mental health factors. Design, Setting, and Participants: This cohort study analyzed data from the Millennium Cohort Study, an ongoing prospective longitudinal study of US service members from all military branches. Participants were enrolled in 4 phases from July 1, 2001, to April 4, 2013, and completed a self-administered survey at enrollment and every 3 to 5 years thereafter. The population for the present study was restricted to active-duty service members from the first 4 enrollment phases who deployed in support of the wars in Iraq and Afghanistan. Questionnaire data were linked with medical encounter data through September 30, 2015. Data analyses were conducted from January 10, 2017, to December 14, 2020. Exposures: Combat exposure was examined in 3 ways (any combat experience, overall combat severity, and 13 individual combat experiences) using a 13-item self-reported combat measure. Main Outcomes and Measures: Suicide attempts were identified from military electronic hospitalization and ambulatory medical encounter data using the International Classification of Diseases, Ninth Revision codes. Results: Among 57 841 participants, 44 062 were men (76.2%) and 42 095 were non-Hispanic White individuals (72.8%), and the mean (SD) age was 26.9 (5.3) years. During a mean (SD) follow-up period of 5.6 (4.0) years, 235 participants had a suicide attempt (0.4%). Combat exposure, defined broadly, was not associated with suicide attempts in Cox proportional hazards time-to-event regression models after adjustments for demographic and military-specific factors; high combat severity and certain individual combat experiences were associated with an increased risk for suicide attempts. However, these associations were mostly accounted for by mental disorders, especially posttraumatic stress disorder. After adjustment for mental disorders, combat experiences with significant association with suicide attempts included being attacked or ambushed (hazard ratio [HR], 1.55; 95% CI, 1.16-2.06), seeing dead bodies or human remains (HR, 1.34; 95% CI, 1.01-1.78), and being directly responsible for the death of a noncombatant (HR, 1.81; 95% CI, 1.04-3.16). Conclusions and Relevance: This study suggests that deployed service members who experience high levels of combat or are exposed to certain types of combat experiences (involving unexpected events or those that challenge moral or ethical norms) may be at an increased risk of a suicide attempt, either directly or mediated through a mental disorder.

Multiple imputation validation study: addressing unmeasured survey data in a longitudinal design.

BACKGROUND: Questionnaires used in longitudinal studies may have questions added or removed over time for numerous reasons. Data missing completely at a follow-up survey is a unique issue for longitudinal studies. While such excluded questions lack information at one follow-up survey, they are collected at other follow-up surveys, and covariances observed at other follow-up surveys may allow for the recovery of the missing data. This study utilized data from a large longitudinal cohort study to assess the efficiency and feasibility of using multiple imputation (MI) to recover this type of information. METHODS: Millennium Cohort Study participants completed the 9-item Patient Health Questionnaire (PHQ) depression module at 2 time points (2004, 2007). The suicidal ideation item in the module was set to missing for the 2007 assessment. Several single-level MI models using different sets of predictors and forms of suicidal ideation were used to compare self-reported values and imputed values for this item in 2007. Additionally, associations with sleep duration and smoking status, which are related constructs, were compared between self-reported and imputed values of suicidal ideation. RESULTS: Among 63,028 participants eligible for imputation analysis, 4.05% reported suicidal ideation on the 2007 survey. The imputation models successfully identified suicidal ideation, with a sensitivity ranging between 34 and 66% and a positive predictive value between 36 and 42%. Specificity remained above 96% and negative predictive value above 97% for all imputed models. Similar associations were found for all imputation models on related constructs, though the dichotomous suicidal ideation imputed from the model using only PHQ depression items yielded estimates that were closest with the self-reported associations for all adjusted analyses. CONCLUSIONS: Although sensitivity and positive predictive value were relatively low, applying MI techniques allowed for inclusion of an otherwise missing variable. Additionally, correlations with related constructs were estimated near self-reported values. Therefore, the other 8 depression items can be used to estimate suicidal ideation that was completely missing from a survey using MI. However, these imputed values should not be used to estimate population prevalence.

Smoking Among U.S. Service Members Following Transition From Military to Veteran Status.

Smoking rates among U.S. Service members and veterans have been consistently higher than in civilian populations. While much has been published about tobacco use in both military and veteran populations, smoking patterns during transition from military to veteran status remains unclear. We studied military members participating in the Millennium Cohort Study, who separated from their respective Services between baseline and first follow-up survey (N = 5,510). Two generalized estimating equation models were used to examine any association between smoking status and time to military separation (days between baseline survey and separation), as well as smoking during transition and reason for separation. Reason for separation was categorized into three groups: (1) not meeting military standards or judicial-related reasons, (2) drugs-/alcohol-related misconduct, and (3) other types of separation including retirement, pregnancy, and so on. Statistical models accounted for baseline smoking and demographic/military/health behavioral/mental health characteristics. Overall, we observed a decline in smoking prevalence over time (19.5%, 16.7%, 15.2%, and 12.6%, respectively). However, we found a 22% increase in the odds of smoking among those who stayed in the military between 3 months and 1 year, compared to those who stayed 2+ years. Additionally, participants separating for standard/judicial reason(s) showed 69% increased smoking compared to those with other reasons for separation. The time period immediately prior to Service separation and certain types of separation were associated with increased odds of smoking. Thus, smoking cessation interventions should target Service members during this transition period to potentially reduce smoking prevalence after separation.

New-Onset Asthma and Combat Deployment: Findings From the Millennium Cohort Study.

Recent reports suggest US military service members who deployed in support of the recent conflicts in Iraq and Afghanistan have higher rates of new-onset asthma than those who did not deploy. However, it is unknown whether combat experiences, in addition to deployment, contribute to new-onset asthma risk. This study aimed to longitudinally determine the risk factors for developing asthma, including combat deployment (categorized as deployed with combat experience, deployed without combat experience, or nondeployed), among participants in the Millennium Cohort Study from 2001 to 2013. A total of 75,770 participants completed a baseline survey and at least 1 triennial follow-up survey on deployment experiences, lifestyle characteristics, and health outcomes. Complementary log-log models stratified by sex were used to estimate the relative risk of developing asthma among participants who reported no history of asthma at baseline. In models with adjustments, those who deployed with combat experience were 24%-30% more likely to develop asthma than those who did not deploy. Deployed personnel without combat experience were not at a higher risk for new-onset asthma compared with nondeployers. Further research is needed to identify specific features of combat that are associated with greater asthma risk to inform prevention strategies.

Smoking and drinking behaviors of military spouses: Findings from the Millennium Cohort Family Study.

INTRODUCTION: The associations between stressful military experiences and tobacco use and alcohol misuse among Service members are well documented. However, little is known about whether stressful military experiences are associated with tobacco use and alcohol misuse among military spouses. METHODS: Using 9872 Service member-spouse dyads enrolled in the Millennium Cohort Family Study, we employed logistic regression to estimate the odds of self-reported cigarette smoking, risky drinking, and problem drinking among spouses by Service member deployment status, communication regarding deployment, and stress associated with military-related experiences, while adjusting for demographic, mental health, military experiences, and Service member military characteristics. RESULTS: Current cigarette smoking, risky drinking, and problem drinking were reported by 17.2%, 36.3%, and 7.3% of military spouses, respectively. Current deployment was not found to be associated with spousal smoking or drinking behaviors. Communication about deployment experiences with spouses was associated with lower odds of smoking, but not with risky or problem drinking. Spouses bothered by communicated deployment experiences and those who reported feeling very stressed by a combat-related deployment or duty assignment had consistently higher odds of both risky and problem drinking. CONCLUSIONS: Our findings suggest that contextual characteristics about the deployment experience, as well as the perceived stress of those experiences, may be more impactful than the simple fact of Service member deployment itself. These results suggest that considering the impact of deployment experiences on military spouses reveals important dimensions of military community adaptation and risk.

A Decade of War: Prospective Trajectories of Posttraumatic Stress Disorder Symptoms Among Deployed US Military Personnel and the Influence of Combat Exposure.

Posttraumatic stress disorder (PTSD) is a common psychiatric disorder among service members and veterans. The clinical course of PTSD varies between individuals, and patterns of symptom development have yet to be clearly delineated. Previous studies have been limited by convenience sampling, short follow-up periods, and the inability to account for combat-related trauma. To determine the trajectories of PTSD symptoms among deployed military personnel with and without combat exposure, we used data from a population-based representative sample of 8,178 US service members who participated in the Millennium Cohort Study from 2001 to 2011. Using latent growth mixture modeling, trajectories of PTSD symptoms were determined in the total sample, as well as in individuals with and without combat exposure, respectively. Overall, 4 trajectories of PTSD were characterized: resilient, pre-existing, new-onset, and moderate stable. Across all trajectories, combat-deployed service members diverged from non-combat-deployed service members, even after a single deployment. The former also generally had higher PTSD symptoms. Based on the models, nearly 90% of those without combat exposure remained resilient over the 10-year period, compared with 80% of those with combat exposure. Findings demonstrate that although the clinical course of PTSD symptoms shows heterogeneous patterns of development, combat exposure is uniformly associated with poor mental health.

Patterns of Smoking and Unhealthy Alcohol Use Following Sexual Trauma Among U.S. Service Members.

In the first known longitudinal study of the topic, we examined whether experiencing sexual assault or sexual harassment while in the military was associated with increased risk for subsequent unhealthy alcohol use and smoking among U.S. service members in the Millennium Cohort Study (2001-2012). Adjusted complementary log-log models were fit to estimate the relative risk of (a) smoking relapse among former smokers (men: n = 4,610; women: n = 1,453); (b) initiation of unhealthy alcohol use (problem drinking and/or drinking over recommended limits) among those with no known history of unhealthy alcohol use (men: n = 8,459; women: n = 4,816); and (c) relapse among those previously reporting unhealthy alcohol use (men: n = 3,487; women: n = 1,318). Men who reported experiencing sexual assault while in the military had sixfold higher risk for smoking relapse: relative risk (RR) = 6.62; 95% confidence interval (CI) [2.34, 18.73], than men who did not. Women who reported experiencing sexual assault while in the military had almost twice the risk for alcohol relapse: RR = 1.73; 95% CI [1.06, 2.83]. There were no other significant associations. These findings suggest that men and women may respond differently following sexual trauma, and support future concerted policy efforts by military leadership to prevent, detect, and intervene on sexual assault.

Risk Factors Associated with Miscarriage and Impaired Fecundity among United States Servicewomen during the Recent Conflicts in Iraq and Afghanistan.

BACKGROUND: Research on the reproductive health of U.S. servicewomen deployed in support of the recent operations in Iraq and Afghanistan is sparse. The objective of this study was to evaluate whether military experiences, including combat deployment, deployment length, and life stressors during the recent conflicts, were associated with increased odds for miscarriage or impaired fecundity among U.S. servicewomen. METHODS: We used data from the Millennium Cohort Study, a large longitudinal military study that began in 2001 and includes military personnel from all service branches, including active duty and Reserve/National Guard personnel. Participants for this study included women aged 18 to 45 years who had completed two questionnaires (2004-2006 and 2007-2008). Separate multivariable logistic regression models were performed to estimate the odds of reporting miscarriage and impaired fecundity by military experiences that adjusted for covariates. Subanalyses were conducted using International Classification of Diseases, Ninth Revision, Clinical Modification codes found in the Military Health System Data Repository for both outcomes among servicewomen on active duty. RESULTS: Overall, 31% and 11% of military servicewomen reported miscarriage and impaired fecundity, respectively, during the approximate 3-year follow-up period. After adjusting for demographic, behavioral, and military characteristics, deployment experiences and life stressors were not associated with miscarriage or perceived impaired fecundity. Subanalyses using medical record data confirmed these results. CONCLUSIONS: Overall, these results suggest that military deployments do not increase risk for miscarriage and impaired fecundity among U.S. servicewomen. However, because the point estimates for many of the exposures were elevated, more research is needed to better understand the potential risks associated with environmental exposures and specific types of combat exposures.

Mental Health and Comorbidities in U.S. Military Members.

OBJECTIVES: Using data from a prospective cohort study of U.S. service members who joined after September 11, 2001 to determine incidence rates and comorbidities of mental and behavioral disorders. METHODS: Calculated age and sex adjusted incidence rates of mental and behavioral conditions determined by validated instruments and electronic medical records. RESULTS: Of 10,671 service members, 3,379 (32%) deployed between baseline and follow-up, of whom 49% reported combat experience. Combat deployers had highest incidence rates of post-traumatic stress disorder (PTSD) (25 cases/1,000 person-years [PY]), panic/anxiety (21/1,000 PY), and any mental disorder (34/1,000 PY). Nondeployers had substantial rates of mental conditions (11, 13, and 18 cases/1,000 PY). Among combat deployers, 12% screened positive for mental disorder, 59% binge drinking, 16% alcohol problem, 19% cigarette smoking, and 20% smokeless tobacco at follow-up. Of those with recent PTSD, 73% concurrently developed >1 incident mental or behavioral conditions. Of those screening positive for PTSD, 11% had electronic medical record diagnosis. CONCLUSIONS: U.S. service members joining during recent conflicts experienced high rates of mental and behavioral disorders. Highest rates were among combat deployers. Most cases were not represented in medical codes, suggesting targeted interventions are needed to address the burden of mental disorders among service members and Veterans.

Chronic multisymptom illness: a comparison of Iraq and Afghanistan deployers with veterans of the 1991 Gulf War.

Symptoms and illnesses reported by veterans of the 1991 Gulf War era are a cause of potential concern for those military members who have deployed to the Gulf region in support of more recent contingency operations in Iraq and Afghanistan. In the present study, we quantified self-reported symptoms from participants in the Millennium Cohort Study, a prospective study representing all US service branches, including both active duty and Reserve/National Guard components (2001-2008). Self-reported symptoms were uniquely compared with those in a cohort of subjects from the 1991 Gulf War to gain context for the present report. Symptoms were then aggregated to identify cases of chronic multisymptom illness (CMI) based on the case definition from the Centers for Disease Control and Prevention. The prevalence of self-reported CMI symptoms was compared with that collected in 1997-1999 from a study population of US Seabees from the 1991 Gulf War, as well as from deployed and nondeployed subgroups. Although overall symptom reporting was much less in the Millennium Cohort than in the 1991 Gulf War cohort, a higher prevalence of reported CMI was noted among deployed compared with nondeployed contemporary cohort members. An increased understanding of coping skills and resilience and development of well-designed screening instruments, along with appropriate clinical and psychological follow-up for returning veterans, might help to focus resources on early identification of potential long-term chronic disease manifestations.

Risk factors associated with suicide in current and former US military personnel.

IMPORTANCE: Beginning in 2005, the incidence of suicide deaths in the US military began to sharply increase. Unique stressors, such as combat deployments, have been assumed to underlie the increasing incidence. Previous military suicide studies, however, have relied on case series and cross-sectional investigations and have not linked data during service with postservice periods. OBJECTIVE: To prospectively identify and quantify risk factors associated with suicide in current and former US military personnel including demographic, military, mental health, behavioral, and deployment characteristics. DESIGN, SETTING, AND PARTICIPANTS: Prospective longitudinal study with accrual and assessment of participants in 2001, 2004, and 2007. Questionnaire data were linked with the National Death Index and the Department of Defense Medical Mortality Registry through December 31, 2008. Participants were current and former US military personnel from all service branches, including active and Reserve/National Guard, who were included in the Millennium Cohort Study (N = 151,560). MAIN OUTCOMES AND MEASURES: Death by suicide captured by the National Death Index and the Department of Defense Medical Mortality Registry. RESULTS: Through the end of 2008, findings were 83 suicides in 707,493 person-years of follow-up (11.73/100,000 person-years [95% CI, 9.21-14.26]). In Cox models adjusted for age and sex, factors significantly associated with increased risk of suicide included male sex, depression, manic-depressive disorder, heavy or binge drinking, and alcohol-related problems. None of the deployment-related factors (combat experience, cumulative days deployed, or number of deployments) were associated with increased suicide risk in any of the models. In multivariable Cox models, individuals with increased risk for suicide were men (hazard ratio [HR], 2.14; 95% CI, 1.17-3.92; P = .01; attributable risk [AR], 3.5 cases/10,000 persons), and those with depression (HR, 1.96; 95% CI, 1.05-3.64; P = .03; AR, 6.9/10,000 persons), manic-depressive disorder (HR, 4.35; 95% CI, 1.56-12.09; P = .005; AR, 35.6/10,000 persons), or alcohol-related problems (HR, 2.56; 95% CI, 1.56-4.18; P <.001; AR, 7.7/10,000 persons). A nested, matched case-control analysis using 20:1 control participants per case confirmed these findings. CONCLUSIONS AND RELEVANCE: In this sample of current and former military personnel observed July 1, 2001-December 31, 2008, suicide risk was independently associated with male sex and mental disorders but not with military-specific variables. These findings may inform approaches to mitigating suicide risk in this population.

Prospective assessment of chronic multisymptom illness reporting possibly associated with open-air burn pit smoke exposure in Iraq.

OBJECTIVE: To investigate the relationship between chronic multisymptom illness (CMI) and possible exposure to an open-air burn pit at three selected bases among those deployed to operations in Iraq and Afghanistan. METHODS: Chronic multisymptom illness (reporting at least one symptom in at least two of the following symptom constructs: general fatigue; mood and cognition problems; and musculoskeletal discomfort) was assessed, differentiating by potential burn pit exposure, among deployers who completed 2004 and 2007 Millennium Cohort questionnaires. RESULTS: More than 21,000 Cohort participants were deployed in support of the current operations, including more than 3000 participants with at least one deployment within a 3-mile radius of a documented burn pit. After adjusting for covariates, no elevated risk of CMI was observed among those exposed. CONCLUSIONS: There was no increase in CMI symptom reporting in those deployed to three selected bases with documented burn pits compared with other deployers.

Trajectories of trauma symptoms and resilience in deployed U.S. military service members: prospective cohort study.

BACKGROUND: Most previous attempts to determine the psychological cost of military deployment have been limited by reliance on convenience samples, lack of pre-deployment data or confidentiality and cross-sectional designs. AIMS: This study addressed these limitations using a population-based, prospective cohort of U.S. military personnel deployed in support of the operations in Iraq and Afghanistan. METHOD: The sample consisted of U.S. military service members in all branches including active duty, reserve and national guard who deployed once (n = 3393) or multiple times (n = 4394). Self-reported symptoms of post-traumatic stress were obtained prior to deployment and at two follow-ups spaced 3 years apart. Data were examined for longitudinal trajectories using latent growth mixture modelling. RESULTS: Each analysis revealed remarkably similar post-traumatic stress trajectories across time. The most common pattern was low-stable post-traumatic stress or resilience (83.1% single deployers, 84.9% multiple deployers), moderate-improving (8.0%, 8.5%), then worsening-chronic post-traumatic stress (6.7%, 4.5%), high-stable (2.2% single deployers only) and high-improving (2.2% multiple deployers only). Covariates associated with each trajectory were identified. CONCLUSIONS: The final models exhibited similar types of trajectories for single and multiple deployers; most notably, the stable trajectory of low post-traumatic stress preto post-deployment, or resilience, was exceptionally high. Several factors predicting trajectories were identified, which we hope will assist in future research aimed at decreasing the risk of post-traumatic stress disorder among deployers.