A pollster hired by Kansas Secretary of State Kris Kobach testified Monday that a survey of 500 adults he conducted found just one person who couldn't produce a document proving U.S. citizenship.

The Topeka Capital-Journal reported his testimony came on the seventh day of a federal bench trial challenging Kansas' proof-of-citizenship requirement.

Pollster Pat McFerron also acknowledged possible bias in his survey under questioning by an attorney for the American Civil Liberties Union.

U.S. District judge Julie Robinson allowed McFerron to testify, even though he was not identified as an expert witness before the deadline that had been set by the judge.

McFerron is president of Cole Hargrave Snodgrass, a firm that primarily caters to Republican candidates. He was paid $9,000 for his survey.

One of the survey questions asked: "In 2011, because of evidence that aliens were registering and voting in Kansas elections, the Kansas Legislature passed a law requiring that people who register to vote for the first time must prove that they are United States citizens before they can become registered. Do you support or oppose this?"

Seventy-seven percent supported the law, 14 percent opposed and 9 percent had no opinion.

Citing the wording of the survey question, ACLU attorney Neil Steiner asked whether it introduces bias into the survey. McFerron agreed it could.