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

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. 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 > or =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. 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). 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.