Quinnipiac University economist Mark Gius has published a new study, "An examination of the effects of concealed weapons laws and assault weapons bans on state-level murder rates," in the journal Applied Economics Letters. From the abstract:
The purpose of the present study is to determine the effects of state-level assault weapons bans and concealed weapons laws on state-level murder rates. Using data for the period 1980 to 2009 and controlling for state and year fixed effects, the results of the present study suggest that states with restrictions on the carrying of concealed weapons had higher gun-related murder rates than other states. It was also found that assault weapons bans did not significantly affect murder rates at the state level. These results suggest that restrictive concealed weapons laws may cause an increase in gun-related murders at the state level. The results of this study are consistent with some prior research in this area, most notably Lott and Mustard (1997).
For more background: The most recent Reason-Rupe poll reports that 63 percent of Americans don't believe that stricter gun laws would keep weapons out of the hands of criminals.