Shapiro decided to test her hypothesis by studying the effects of EMDR therapy on a group of Vietnam veterans, as well as on victims of physical and sexual abuse. All suffered from PTSD and had difficulty concentrating. After only a single, 60-minute session, Shapiro reported, those individuals who received treatment with rapid eye movements described a significant reduction in PTSD symptoms compared to members of a control group who were asked to recall the traumatic memory, but without the eye movements. Today some studies have corroborated the success of Shapiro's method in treating trauma due to many causes, including loss of a loved one, sexual assault, accidents, combat trauma, and natural disasters. However, conflicting studies have also found equal success in PTSD groups where no rapid eye movements or other external stimulus were employed. Further studies are ongoing to determine the necessity of external stimuli in EMDR therapy for PTSD and lesser trauma (see Health Benefits, below).