In the US, researching the interaction between regulations and gun violence is incredibly challenging.
A patchwork of state and local regulations complicates finding populations that can be used to track any changes in response to new legislation.
And, since 1996, federal funding for the research has been nearly nonexistent.
Nevertheless, the researchers that have found money to study the subject sometimes do get a bit of a break. One of those occurred in 2007, when the state of Missouri repealed regulations on the purchase of guns that had been in place since 1921. Daniel Webster of the Johns Hopkins School of Public Health described the consequences of this change at the meeting of the American Association for the Advancement of Science.
The US limits on gun research date back to a 1993 study funded by the CDC, which found that guns in the home were associated with an increased risk for homicide.
After an attempt to eliminate the CDC’s National Center for Injury Prevention failed, Congress simply eliminated all the money that had been used to fund gun research there and directed that “none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control.” Those prohibitions remain in place.