The researchers at CCES (including Schaffner; Stephen Ansolabehere, a Harvard political scientist; and Samantha Luks, a statistician at YouGov) have criticized the methodology used by Old Dominion.

They said it didn’t fully consider the possibility that people responded to the survey inaccurately.

"You are ignoring the measurement error in a very small group which is going to inflate those numbers," Schaffner said, "then you assume this is a random sample of all noncitizens in the country, which it probably isn’t."

More than 100 political scientists from universities and colleges wrote an open letter in January disputing the Old Dominion paper as evidence for Trump’s claim that millions of noncitizens voted.

"In a survey as large as the CCES, even a small rate of response error (where people incorrectly mark the wrong item on a survey) can lead to incorrect conclusions," they wrote. "The scholarly political science community has generally rejected the findings in the Richman et al. study and we believe it should not be cited or used in any debate over fraudulent voting."

Jesse Richman, one of the Old Dominion researchers and a political science professor, told PolitiFact he still stands by his research and responded to the criticisms by CCES researchers in a working paper in February.