Unit cohesion during deployment and post-deployment mental health: is cohesion an individual- or unit-level buffer for combat-exposed soldiers?

Abstract

Background: Unit cohesion may protect service member mental health by mitigating effects of combat exposure; however, questions remain about the origins of potential stress-buffering effects. We examined buffering effects associated with two forms of unit cohesion (peer-oriented horizontal cohesion and subordinate-leader vertical cohesion) defined as either individual-level or aggregated unit-level variables.

Methods: Longitudinal survey data from US Army soldiers who deployed to Afghanistan in 2012 were analyzed using mixed-effects regression. Models evaluated individual- and unit-level interaction effects of combat exposure and cohesion during deployment on symptoms of post-traumatic stress disorder (PTSD), depression, and suicidal ideation reported at 3 months post-deployment (model n's = 6684 to 6826). Given the small effective sample size (k = 89), the significance of unit-level interactions was evaluated at a 90% confidence level.

Results: At the individual-level, buffering effects of horizontal cohesion were found for PTSD symptoms [B = -0.11, 95% CI (-0.18 to -0.04), p < 0.01] and depressive symptoms [B = -0.06, 95% CI (-0.10 to -0.01), p < 0.05]; while a buffering effect of vertical cohesion was observed for PTSD symptoms only [B = -0.03, 95% CI (-0.06 to -0.0001), p < 0.05]. At the unit-level, buffering effects of horizontal (but not vertical) cohesion were observed for PTSD symptoms [B = -0.91, 90% CI (-1.70 to -0.11), p = 0.06], depressive symptoms [B = -0.83, 90% CI (-1.24 to -0.41), p < 0.01], and suicidal ideation [B = -0.32, 90% CI (-0.62 to -0.01), p = 0.08].

Conclusions: Policies and interventions that enhance horizontal cohesion may protect combat-exposed units against post-deployment mental health problems. Efforts to support individual soldiers who report low levels of horizontal or vertical cohesion may also yield mental health benefits.

Keywords: Depression; military personnel; multilevel analysis; post-traumatic stress disorder; protective factors; psychological resilience; risk factors; suicidal ideation.

Figures

Figure 1.

Illustration of the individual-level and unit-level interaction effects of combat exposure and horizontal cohesion on symptoms of PTSD (panel A) and depression (panel B) at 3 months post-deployment. Dotted lines show the predicted levels of symptoms for individuals scoring 1 SD below the mean (gray line) and 1 SD above the mean black line) on the horizontal cohesion scale. Solid lines show the predicted unit-average symptom scores for units with average horizontal cohesion scores that were 1 SD below the mean (gray line) and 1 SD above the mean (black line) for the 89 units represented in the analytic samples. At the individual level, low combat exposure is defined as 1 SD below the mean and high combat exposure as 1 SD above the mean level of combat exposure reported by the soldiers in each analytic sample. At the unit level, low combat exposure is defined as a unit-average combat exposure score 1 SD below the mean and high combat exposure as a unit-average combat exposure score 1 SD above the mean combat exposure score for all 89 units. Estimates are based on Models 1.2 and 1.4 (panel A) and Models 2.2 and 2.4 (panel B). Subsequent models showed that both the individual- and unit-level interactions were unique predictors of post-deployment PTSD symptoms (panel A) and depressive symptoms (panel B).

Figure 2.

Illustration of the unit-level interaction effect of combat exposure and horizontal cohesion on unit-average suicidal ideation at 3 months post-deployment. The plot shows the predicted unit-average rate of suicidal ideation for units with average horizontal cohesion scores that were 1 SD below (low; gray line) and 1 SD above (high; black line) the mean horizontal cohesion score for all 89 units. Estimates are based on Model 3.4. At the unit level, low combat exposure is defined as a unit-average combat exposure score that is 1 SD below the mean and high combat exposure as a unit-average combat exposure score that is 1 SD above the mean combat exposure score for all 89 units.

Figure 3.

Summary of analytic models and results of analyses of the interactive effects of horizontal cohesion and combat exposure. The statistical interaction between horizontal cohesion and combat exposure was examined in a series of models (Panel A), which varied based on the levels at which cohesion and combat exposure were considered (i.e., group or individual). Results of each model of PTSD symptoms, depressive symptoms, and suicidal ideation are shown in Panel B. X = not statistically significant. ✔ = statistically significant; due to a large discrepancy in effective sample size for individual-level (ns=6,684 to 6,826) and unit-level (k=89) models, alpha was set at p<.05 for raw interaction and cross-level models and at p<.10 for group-mean models.