Researchers have long argued over the effect of allowing more people to legally own and carry guns. But a series of recent studies has found a link between laws that make it easier to carry a handgun and increases in crime, and some have raised the possibility that more guns in circulation lead to more thefts of weapons and to more shootings by the police.

“The weight of the evidence has shifted in the direction that more guns equals more crime,” said John J. Donohue III, a Stanford Law School professor and the author of several recent studies looking at gun regulations and crime.

Much of the research has been around the effects of making handgun licenses easier to obtain, part of what are known as right-to-carry laws, and Mr. Donohue cautioned that only limited data is available on laws that in most cases require no licenses at all.

“I think most people are reasoning by analogy: If you thought that right-to-carry was harmful, this will be worse,” he said.