Stress and Development Lab research has shown that more than 60% of children and adolescents in the United States will experience a traumatic event, such as being the victim of violence or a life-threatening accident or injury, by the time they reach adulthood.  This work identifies risk factors for trauma exposure as well as for the onset of post-traumatic stress disorder (PTSD) among youths who have experienced trauma.  The original paper can be found on the publications page (provide link to pdf to the McLaughlin et al, 2013 paper on trauma exposure and PTSD in a national sample).  The importance of this research for prevention of trauma and PTSD is reviewed by Marylene Cloitre and can be found here.