The rates of mental health morbidity among soldiers and Marines returning from deployment in support of the wars in Iraq and Afghanistan may be as high as 20% [21
]. Two separate investigations described proportions of PTSD between 12.2% and 12.9% in soldiers and Marines 3 to 4 months after combat exposure in OEF/OIF [21
]. The current study of male Marines who deployed for at least 30 days found 10.8% screened positive for PTSD during or following deployment in support of OEF/OIF. Because of the high proportion of PTSD among soldiers and Marines, it is essential to determine factors that protect against or increase the risk for PTSD among these service members.
After adjustment in the regression model, feeling in great danger of death was the strongest independent predictor of PTSD, followed by being shot or seriously injured, prior violence exposures, and personally seeing someone wounded, killed, or dead. These findings are consistent and supportive of results from several earlier studies [6
Using the same strict PCL criteria applied in the current study, Hoge [21
] found that 12.2% of Marines experienced new onset or chronic PTSD symptoms. The slightly lower proportion of postdeployment PTSD symptoms in the current study (10.8%) may reflect slightly lower levels of combat exposures reported by these Marines. While it is difficult to make an exact comparison of exposure histories, since the two studies used different questions to assess combat experiences, the equivalent questions have higher affirmative responses among the population in the Hoge study. For each comparable dimension of combat exposure within the two studies, there appears to be a dose-response phenomenon; greater exposure increases the likelihood for PTSD symptoms.
Traumatic combat exposure alone [6
] is not necessarily a sufficient factor for the development of PTSD. The probability is dependent upon the "range and variance" of traumatic exposure types [40
]. Exposure to violence as a civilian, prior to the Marine Corps training, broadened the range and expanded the exposure types for the cohort subjects. As we describe, reporting between 2 to 7 violence episodes was strongly associated with postdeployment PTSD. These antecedent violence exposures may represent the "building block" effect [41
], perhaps the consequence of a neural fear network, enlarged in response to new traumatic events and types [42
Social support was assessed at baseline and follow-up by asking responders about the number of close friends or relatives they can call or ask for help when they have a problem. There was no association of baseline social support with screening positive for postdeployment PTSD. Interestingly, and consistent with previous research that describes the buffering effect of social support on PTSD symptoms [15
], we found that reporting 0 to 2 close friends or relatives at follow-up was associated with a non significant increase in odds for PTSD, while reporting 5 or more close friends/relatives was associated with a significant reduction in odds for PTSD. Summarized literature suggests an interactive cycle between social support resources and PTSD in which either can influence the nature or expression of the other [48
]. The disorder itself is defined by feelings of detachment or estrangement from others, with half of the six required symptoms for a positive PCL-C screen being expressions of avoidance. There is evidence that a strong social support network, indicated by unit cohesion, is protective [49
], a large social support network may diminish the association between stressful life events and PTSD symptoms. Whether PTSD leads to social avoidance behaviors, or a large social support network with trusted friends and relatives who lessen the opportunity for detachment and estrangement reduces the likelihood of developing PTSD cannot be definitively determined from this study. Social support was measured at baseline and follow-up in this study, however the baseline assessment may not accurately reflect the number of close friends and relatives a Marine has immediately prior to deployment since the baseline survey was completed during the first days of Marine Corps training. The follow-up assessment of social support was ascertained at the same time as PTSD, so while we suspect the association with smaller social support networks measured at follow-up is a consequence of PTSD, we cannot be certain. Longitudinal studies that can better control for predeployment assessed levels of social support, during deployment, and in the immediate postdeployment period are crucial to understanding the influence of social support on symptom mediation [50
Consistent with previous studies and independent of age, higher ranking noncommissioned officers (E4-E5) had decreased odds for PTSD compared with junior enlisted Marines (E1-E3) [15
]. It is likely that the same qualities valued by Marines that are indicative of excellence amongst their ranks, such as mental stamina and competency, enhance their promotion potential, and may also increase resiliency to developing PTSD [45
]. In this study, we were able to control for predeployment rank, since all responders were recruits at baseline, but future longitudinal studies could examine how quickly Marines are promoted to further investigate this relationship.
Marines with two deployments were at a significant increase in odds for a positive PTSD screen. Multiple, not solitary, deployments have become more common as the conflicts in Iraq and Afghanistan continue. It is reasonable to speculate that additional deployments increase the probability for exposure to additional or more traumatic events such as witnessing death, being shot or seriously wounded, or fearing one's own impending death. Indeed, this proved to be true for the study cohort. On average, those deployed once experienced 1.76 combat exposure types while Marines who deployed twice experienced 2.83 combat exposure types.
There are several limitations to this study that should be noted. Participants in the study were a self-selected cohort who consented to participate after invitation in the RAP II survey. The survey was not anonymous, which may have led, due to fear of stigma and reticence, an underreporting of sensitive topics, including adverse childhood symptoms and PTSD symptoms. This lack of anonymity may have been a factor in the low 13% response rate as well. While responders were slightly more likely to be younger and have more than a high school education, the current analysis compensated for these differences with sampling weights. Moreover, the prevalence of PTSD symptoms in this population may be incorrectly estimated secondary to the higher proportions of younger and more educated Marines than are typically represented in the enlisted US Marine Corps. While Marines who successfully complete basic training are assumed to be of good health, PTSD symptoms were not assessed before deployment, therefore no baseline burden was available to estimate new onset of postdeployment PTSD symptoms. We examined a summed score of the different combat exposures types; however, we could not assess the frequency of each exposure or measure the degree of distress for each exposure event. The same exposure could have been perceived as more or less distressing by different subjects, and vary within the same subject at different times. Another limitation of this study is that we did not have the available data to develop measurement scales that meet the standards of psychometric principles, nor were our deployment exposure variables based on an established instrument with proven psychometric properties. For example, we did not have (1) multiple waves of data to test for the reliability of our measures over time (test-retest reliability); (2) the benefit of a large number of measures tapping the same latent construct to develop scales that were internally consistent; nor (3) any data to validate our exposure measures against established instruments with proven psychometric properties. However, our use of single item exposure variables did reflect systematic variation across the study cohort and yielded meaningful results. Responders were all male Marines, so inferences from these data to female Marines and other service branches must be considered with caution. Although the PCL-C is a surrogate for a clinician's diagnosis and may misclassify PTSD status for some responders, it is a standardized instrument that has been validated in other populations [30
]. Finally, exposures and some covariates were from self-reported data, which inherently have some recall and reporting biases.
Despite these limitations, this study had many strengths. Baseline and follow-up survey data as well as electronic military data were available on multiple metrics, which allowed for adequately addressing many potential confounders. Weighting was employed to reduce potential nonresponse bias. Additionally, the survey instruments contained many exposure questions which allowed the current study to uniquely address deployment experiences beyond whether they were in combat situations. Most research thus far has focused on predictors of PTSD that occurred during or after the traumatic exposure; the assessment of exposure to violence as civilians, prior to Marine Corps training, allowed us to account for the predeployment exposure to violence. PCL-C screening for PTSD may more accurately capture those with PTSD symptoms compared with ascertainment via ambulatory or hospitalization data, since many patients with symptoms may not seek treatment. Our survey captured many of the participants approximately 3 months after return from deployment and likely represents the optimal time window to ascertain PTSD symptoms [21