And I don't mean that in a lighthearted way. You feel secure about some 'fact,' then you look at the actual data and discover things aren't really that way. Barber cites examples from motor vehicles. Inspections and drivers' education do not lower fatalities as much as expected. Motorcycle helmets really matter in accidents, and raising speed limits produces a predictable increase in highway deaths.
Air bags offer less protection than first believed, and they can even kill people.
The first step in obtaining that kind of information about firearms involves getting each state to report the same information in the same way. That means getting coroners', medical examiners', police, crime lab, and vital statistics reports all in the same form. In one state with 120 counties, the murders were carefully documented in each county, but the information was in different drawers, boxes, filing cabinets and computer systems. Multiply that by 50, and you get a feeling for the enormity of the problem. Information on factors such as involvement of drugs and alcohol, relationships between shooters and their victims, and extent of depression in suicide cases all had to be standardized.