Foy, D. W., Sipprelle, R. C., Rueger, D. B., & Carroll, E. M. (1984). Etiology of Posttraumatic Stress Disorder in Vietnam veterans: Analysis of premilitary, military, and combat exposure influences. Journal of Consulting & Clinical Psychology, 52(1), 79–87. American Psychological Assn, US,  http://www.apa.org