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

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.