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Population Estimates of Undocumented Incident Traumatic Brain Injuries Among Combat-Deployed US Military Personnel

Chase, Rachel P. BSc; Nevin, Remington L. MD, MPH

The Journal of Head Trauma Rehabilitation: January/February 2015 - Volume 30 - Issue 1 - p E57–E64
doi: 10.1097/HTR.0000000000000061
Original Articles

Objective: To estimate the number of undocumented incident traumatic brain injuries (TBIs) among active component US military personnel serving in Iraq and Afghanistan prior to policy changes implemented in late 2006 and 2010 that improved TBI documentation.

Methods: Negative binomial regression was used to model monthly incident TBI counts between December 2010 and June 2012 (N = 19) and then estimate expected monthly counts of incident TBIs during 2 periods: January 2003-October 2006 and November 2006-November 2010. Monthly amputation counts from Department of Defense surveillance data were used as a proxy for changing injury rates. Monthly active component deployment estimates derived from the Congressional Research Service, Brookings Institution, and Defense Manpower Data Center were used to estimate the size of the at-risk population each month. The difference between expected monthly incident TBI counts and reported counts is presented as the estimated number of undocumented incident TBIs.

Results: The full model estimates that 21 257 active component military personnel experienced undocumented incident TBIs while deployed in Iraq or Afghanistan between January 2003 and October 2006, more than 4 times the 5272 incident TBIs documented during that period.

Conclusions: A sizeable majority of Iraq and Afghanistan combat veterans who experienced incident TBI while deployed prior to November 2006 are likely to have had their injuries undocumented, creating challenges for clinical care, disability evaluation, and future research.

Departments of International Health (Ms Chase) and Mental Health (Dr Nevin), Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.

Corresponding Author: Rachel P. Chase, BSc, Department of International Health, Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD 21205 (

The authors thank Shannon McMahon and Roger Peng for their helpful comments during manuscript preparation and review and the 3 anonymous reviewers for their valuable recommendations. The authors are also indebted to the staff of the Armed Forces Health Surveillance Center for providing the monthly traumatic brain injury and amputation count data on which these analyses are based.

Dr Nevin reports serving as consultant and expert witness in cases involving claims of antimalarial toxicity, a relevant conflict given the potential for confounding of this condition with traumatic brain injury in military populations. Ms Chase reports no conflicts of interest. This work was conducted without external funding.

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