While Congress has been caught in a perpetual argument over whether to require background checks for all gun sales, several states have already acted. Those that have added additional background check laws regarding private gun sales tend to have lower gun death rates.

Why it matters: Of course, correlation doesn't equal causation, but typically trends like this at least spark smart, nuanced research. Gun deaths are comparatively under-researched, and gun debates on Capitol Hill are based more on emotions than the facts and trends we do know.

“There is research that does suggest that background checks can be effective in reducing firearm violence.”

— Michael Siegel, professor at Boston University School of Public Health