This document discusses several studies on post-traumatic stress disorder (PTSD) in military veterans of war. It examines the differences in PTSD between veterans who served in active combat zones versus non-active combat zones. One study found that PTSD symptoms were significantly more severe, on average, for veterans who served in active combat zones where there was regular firefights, bombings and IEDs. To better understand the causes of PTSD and improve treatment, the document proposes a study comparing PTSD rates and diagnoses between veterans from active and non-active combat deployments. The results are hypothesized to show that active combat exposure leads to higher rates of PTSD.