MARK KLEIMAN has a lengthy post on the John Lott / Stanford Law Review stuff, and many other things Lott-related. He's quite critical of Lott, but notes:
It seems clear that Ayres and Donohue detected a significant coding error in the response, just as Donohue had earlier detected significant coding errors in other work by Lott and Mustard. Moreover, in addition to putting a hole in Lott's earlier work, Ayres and Donohue's analyses of subsequent data suggest that the "more guns, less crime" hypothesis is, at best, true in some places and not in others, and even then to only a slight extent. There is no justification for continuing to claim that Lott has proven that liberalizing concealed-carry reduces crime.
At the end of the day, though, it's pretty clear that if "shall-issue" increases gun violence at all, it doesn't do so by very much. To that limited extent, Lott was right and the gun controllers were wrong.
There's more, and you should read the whole post if you're interested in this subject. I lack the expertise to judge on the coding error issue, and I haven't looked at the data. Kleiman, I believe, has the expertise, but it's not clear if he's looked at the data or is just taking the word of Ian Ayres and John Donohue. I regard Ayres and Donohue as eminently trustworthy -- in the sense of being honest -- but that doesn't guarantee that they're right, of course. I'd like to see some other people looking at the data, which Lott has made freely available, and addressing this issue. Ayres and Donohue have, at the very least, raised doubts that I am not competent to address, and that need to be addressed.