Former President Donald J. Trump has repeatedly stoked fears about a surge of people walking across the U.S. southern border and has singled out one group that he describes as posing a particular threat: migrants from Venezuela.

At the Republican National Convention, with supporters waving signs that read “Mass deportation now,” he repeated a claim for which there is little or no evidence.

Mr. Trump said that crime in Venezuela had declined by 72 percent because the government purged criminals from the country and sent them to the United States. Then he appeared to make a wry joke about a reduction in crime in one country resulting in an increase in another.

“We will have our next Republican convention in Venezuela because it will be safe,” Mr. Trump said when he accepted the Republican Party’s nomination for president. “Our cities will be so unsafe, we will not be able to have it there.”

Yes, but there isn’t reliable information to determine how much or why.

The Venezuelan government, which is notoriously opaque, does not release comprehensive crime figures. In 2010, as the country faced a soaring rate of homicides, the authorities punished news organizations for reporting on violent crime.