Consistent association between mixed lateral preference and PTSD: Confirmation among a national study of 2490 US Army Vietnam veterans

Objective: To evaluate the research-based association between mixed lateral preference for handedness and risk for posttraumatic stress disorder (PTSD) in a large-scale sample of US Army Vietnam veterans exposed to war zone stressors. Method: We used a national sample of 2490 male US Army veterans, who completed the Edinburgh Handedness Inventory (EHI), a measure ranging from -100 (pure left-handedness) to +100 (pure right-handedness). We developed several classifications representing levels of mixed laterality: a) an EHI -70 to +70 (EHI 70, moderate mixed); b) an EHI -50 to +50 (EHI 50, consistent mixed); and c) an EHI 0, plus reports of using either hand on >= 50% of the tasks assessed (EHI 0+, extreme mixed). We controlled for intelligence, race, Army entry age, and Army volunteer status, and we assessed the impact of combat exposure. Results: Although all three handedness measures were associated with current PTSD in bivariate analyses, only Edinburgh 0+ was associated with PTSD in the multivariate model (odds ratio (OR) = 2.1; p = .021). However, when we classified handedness by high combat exposure, all three measures were associated with PTSD, with ORs = 2.5, 2.8, and 4.7 for EHI 70, EHI 50, and EHI 0+, respectively (all p < .001). Veterans with mixed laterality and high combat exposure also had significantly increased PTSD symptoms (all p < .001). Conclusion: Our study confirmed findings reported among mostly smaller clinical samples and suggested that mixed lateral preference was associated with PTSD, especially among those individuals exposed to more severe psychological trauma.