The data that McClatchy obtained from the Department of Veterans Affairs doesn't specify whether a veteran was in combat in Iraq and Afghanistan. While the VA has a category for the wars in Vietnam and Korea as well as World War II and World War I, it lumps all veterans from the first Persian Gulf War and the current conflicts into one category called "Gulf War."

Because its databases are so limited, even the VA can't say whether a veteran it identifies as part of the war on terrorism sustained post-traumatic stress disorder or a back injury from the current wars or from a previous conflict, such as the Persian Gulf War.

For its analysis of 3 million records, McClatchy pulled those of veterans who joined the military after the Persian Gulf War and left it sometime in 2002 or later, after the war in Afghanistan started. It also adjusted for other technical factors related to the VA's computer systems; because of that, some of the analyses include veterans through 2006, while others include veterans through 2007.