Figure. Sample selection flowchart. *Cohort obtained from the U.S. Department of Defense Manpower Data Center, Monterey, California. Deployed cohort included all deployed troops, and nondeployed cohort was approximately half of all nondeployed troops in service between September 1990 and May 1991. Stratified random sampling applied to the U.S. Department of Defense cohort to adequately represent women, reservists, and National Guard members. Stratified random sampling applied to participants in the 1995 study to select by geographic proximity to 1 of 16 participating Veterans Affairs Medical Centers. We initially invited 2084 veterans to participate. To achieve examined groups of equal size, we invited an additional 799 veterans to participate in the fourth solicitation wave of 50 veterans per site.

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