Why don’t we know how many people are shot each year in the U.S.? It would seem that such a question could be answered by a simple search in a government database. However, due to conflicting reports and figures distributed by different entities, that number is impossible to determine.

There are reliable estimates on the number of fatal shootings—but what about those who survived?

The Department of Justice has estimates that suggest a decline in the number of non-fatal shooting: Its National Crime Victimization Survey shows a decline, from an average of about 22,000 nonfatal shootings in 2002, to roughly 12,000 a year from 2007 to 2011, according to a Department of Justice statistician. However, the DOJ can only collect data on victims with an address or some other form distinguishable identification. Shooting victims are “disproportionately young men of color who are living unstable lives and often involved in underground markets or criminal activity, and this is a group that is incredibly difficult to survey,” said Philip Cook, a gun violence expert at Duke University. “A lot of them are in jail at any point in time, or if they’re not in jail, they have no stable address.”

During the same period, CDC estimates show that the number of Americans coming to hospitals with nonfatal, violent gun injuries has actually gone up: from an estimated 37,321 nonfatal gunshot injuries in 2002 to 55,544 in 2011. But the CDC’s data collection is far from perfect; their data is culled from 63 hospitals nationwide and than extrapolated. CDC’s estimate for non-fatal shootings in 2012 was in between 27,000-91,000, which doesn’t exactly paint an accurate picture of the scene.

An initial push to create a national database of firearm injuries in the late 1980s and early 1990s was slowed by the political fight over Centers for Disease Control and Prevention funding for gun research, according to a history of the project written by researchers who worked on it. To make the effort more politically viable, as well as more scientifically rigorous, researchers decided to collect data on all violent deaths, not just firearm deaths.

Congress did approve funds to begin building a National Violent Death Reporting System in 2002. The push was inspired by a successful effort to track highway vehicle accidents, which experts say has helped reduce the number of deaths from car crashes.

But until last year, the system had only received enough congressional funding to collect detailed data on deaths in 18 states. Then after the Sandy Hook shootings, Congress approved an additional nearly $8 million for database, though that still isn’t enough to detail violent deaths in all 50 states.

A more detailed report can be found at this link.