An investigation by the New York Times found unintentional gun deaths of children were vastly underreported in federal data, compared to individual police reports and death records. The problem seems to be how coroners and medical examiners classify deaths in statistics that are then passed on to the federal government: "Choosing among five options — homicide, accidental, suicide, natural or undetermined — most medical examiners and coroners simply call any death in which one person shoots another a homicide," even if the attached narrative of the death makes it clear it was an accident.
Unfortunately, the Times was only able to use data from five states, as most don't make death certificates public. The local reporting questions become a national policy issue because the NRA uses those low accident statistics to lobby against safe-storage laws, the Times asserts. Regardless of where one stands in the gun-control debate, it would be nice to have more accurate numbers to work with.