Original ArticlesPosttraumatic Stress Disorder Associated With Combat Service in Iraq or Afghanistan: Reconciling Prevalence Differences Between StudiesKok, Brian C. BA; Herrell, Richard K. PhD; Thomas, Jeffrey L. PhD; Hoge, Charles W. MDAuthor Information Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, MD. The views expressed are those of the authors and do not represent the official policy or position of the US Army or the Department of Defense. Send reprint requests to Brian C. Kok, BA, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, 503 Robert Grant Ave, Silver Spring, MD 20910. E-mail: firstname.lastname@example.org. The Journal of Nervous and Mental Disease: May 2012 - Volume 200 - Issue 5 - p 444-450 doi: 10.1097/NMD.0b013e3182532312 Buy Metrics Abstract Studies of posttraumatic stress disorder (PTSD) prevalence associated with deployment to Iraq or Afghanistan report wide variability, making interpretation and projection for research and public health purposes difficult. This article placed this literature within a military context. Studies were categorized according to deployment time-frame, screening case definition, and study group (operational infantry units exposed to direct combat versus population samples with a high proportion of support personnel). Precision weighted averages were calculated using a fixed-effects meta-analysis. Using a specific case definition, the weighted postdeployment PTSD prevalence was 5.5% (95% CI, 5.4–5.6) in population samples and 13.2% (12.8–13.7) in operational infantry units. Both population-level and unit-specific studies provided valuable and unique information for public health purposes; understanding the military context is essential for interpreting prevalence studies. © 2012 Lippincott Williams & Wilkins, Inc.