Is cohesion within military units associated with post-deployment behavioral and mental health outcomes?

•Cohesion is thought to buffer the impact of war stressors on mental health.•Unit and individual level variation in cohesion have not been distinguished.•US Marines was assessed before and after military deployment in 2010 or 2011.•Unit cohesion was unrelated to PTSD symptoms or a depression screen.

PurposePrior studies suggest that cohesion among members of military units has a positive impact on behavioral and mental health sequelae of combat deployment. However, these studies have not distinguished variation in cohesion across units from variation in perception of cohesion across individuals within units.MethodsA sample of U.S. Marines was assessed before and after deployment to Iraq or Afghanistan in 2010 or 2011. Within-group centering was used to distinguish unit-level from individual-level associations of cohesion with four behavioral and mental health outcomes assessed after deployment: alcohol misuse, violation of the Uniform Code of Military Justice (UCMJ), probable posttraumatic stress disorder (PTSD) and a positive screen for depression.ResultsUnit-level cohesion is associated positively with alcohol misuse (OR=1.86, 95% CI 1.05-3.29) and negatively with UCMJ violations (OR=0.41, 95% CI 0.20-0.83) but not with probable PTSD (OR=1.00, 95% CI 0.60-1.6) or a positive screen for depression (OR=1.00 95% CI 0.58-1.72). Lower perception of cohesion relative to the other members of the same unit is associated with higher likelihood of UCMJ violations, probable PTSD and a positive screen for depression.LimitationsData on all members of the studied units were not available.ConclusionsDistinguishing unit-level from individual-level variation in cohesion among military unit members reveals more varied associations with behavioral and mental health outcomes of deployment than have been reported in previous studies, in which these levels have been collapsed. Associations between individual-level variation in cohesion and mental health outcomes may result from pre-existing traits related to both perception of cohesion and risk for psychiatric disorders.