A study by Kovandzic and Marvell has been published in July issue of Criminology and Public Policy. (A draft of their paper is here.) From the journal's news release about their findings:
In the recently published study "Right-to-Carry Concealed Handguns: Crime Control through Gun Decontrol?," Kovandzic and Marvell examine what, if any, impact Florida's right-to-carry law has had on its rate of violent crime. They find that the 1987 passage of Florida's RTC law appears to have had no statistically significant effect on violent crime. They proffer several explanations for the no-effect finding. First, they point out that few people have taken advantage of the concealed carry law? "despite millions of Floridians being eligible for permits... 12 years after the [RTC] law was in effect, there were only 248,O49 valid concealed weapons permits in Florida, representing 2.1% of the Florida adult population." They further speculate that the benefits of allowing potential victims to carry concealed handguns might be cancelled out by an increased number of potential criminals securing permits to carry concealed handguns of their own. Kovandzic and Marvell conclude "there may be numerous reasons for state policymakers to support RTC laws, but the belief that these laws reduce crime should not be one of them."
In one of two 'reaction essays' included in the same issue of Criminology & Public Policy, John J. Donohue of Stanford University calls the Kovandzic and Marvell finding "the final bullet in the body of the more guns, less crime hypothesis."
Donohue's essay is available here. He writes:
One article noted that Lott also points out that because the claim of coding errors appears in a law review, it has not been subject to review by third-party scholars, as would have been the case in a peer reviewed economics journal. David Glenn, Scholarly Debate Over Guns and Crime Rekindles as States Debate Legalization, The Chronicle of Higher Education, April 30, 2003. But Lott doesn't need anyone else to evaluate the claim. He can simply look at the Ayres and Donohue paper and concede (or refute) the claim of coding error, and concede (or refute) that its correction eliminates his more guns, less crime result.
...
But more importantly, when someone's work is being identified as erroneous because of mis-coding errors, one would think that the focus of attention should be directed at either correcting the errors or showing that they do not exist. On this most crucial matter, we have heard nothing from Lott, and we are anxious to hear his response. This is particularly true because the same errors that are found in the paper from which he has removed his name also are found in his newly published book, and because he continues to lobby on behalf of concealed carry laws claiming that they will reduce crime, when his own regressions (when corrected) show that that is not true.