Christopher Ingraham’s “More Guns, More Crime” ignored research critical of a slightly updated, error-ridden paper by law professor John Donohue and two graduate students co-authors. Mr. Ingraham is simply wrong to claim they “now . . . added another full decade to the analysis.” Other already-published studies have considered the same recent data.

Their revised paper’s “preferred” results supposedly show violent crime rates increase after states pass right-to-carry laws. Among the problems:

— They rely, without explanation, on estimates Mr. Donohue has previously claimed were unreliable and misleading. Measuring simply the average crime rates before and after the law can miss an upward trend in crime before the law and drops afterwards.

— They focus on the period from 1999 to 2010. But later-adopting states were often reluctantly dragged into passing these laws. Their laws were more restrictive — higher fees, longer training requirements and more gun-free zones. The authors compare the drop in violent crime for these late adopters with other states — primarily earlier adopters who issued many more permits — who experienced larger drops in crime. But smaller drops for more restrictive states is exactly what the “More Guns, Less Crime” hypothesis predicts.

— Even relying on these flawed estimates, Mr. Ingraham ignored that most of the authors’ results still provide no evidence that violent crime increases.

Two-thirds of peer-reviewed research by economists and criminologists finds that right-to-carry laws reduce violent crime.

Lloyd Cohen, Arlington

The writer is a professor in the School of Law at George Mason University.

John R. Lott Jr., Burke

The writer is president of the Crime Prevention Research Center.

Carl Moody, Williamsburg, Va.

The writer is a professor in the Department of Economics College of William and Mary.