Matt A. Barreto, who conducted the survey for the civil-liberties groups challenging the law in court, testified that the number jumps even higher when the pool is extended to include all eligible voters in Pennsylvania. Under that scenario, 1.36 million residents, or 14.4 percent, lack a valid ID, he said.
Asked if it was possible for state officials to ensure that all registered voters who went to the polls would be able to vote in the Nov. 6 presidential election, Barreto said: "I think that it would be almost impossible for anyone to give that assurance."
His review, conducted in late June and early July, drew on 1,285 randomly selected adults in Pennsylvania, and separately sampled African Americans and Hispanics.
It was completed before the state announced that starting next month, a new voting-only ID, requiring less paperwork, would be offered. At the time of the survey, the state was offering free nondriver photo-ID cards from the Department of Transportation to those who needed one, but that required voters to dig up several official documents, such as Social Security cards and birth certificates.
The professor testified on behalf of the American Civil Liberties Union and other groups that have sued the state to overturn the law before it takes effect this fall. The law requires voters to show an approved form of photo identification at the polls; if they show up without one or can't get one by Nov. 6, they can cast a provisional ballot, and then have six days to produce the necessary ID.
Also testifying Thursday was Rebecca Oyler, director of policy at the Department of State, which oversees Pennsylvania elections.
When the voter law was being debated and passed in the legislature, Gov. Corbett and officials in the Department of State said only about 1 percent of voters did not have the types of ID required by the new law.
Then, in July, the department reported that a comparison of PennDot databases and voter rolls showed up to 9 percent of registered voters might be without either valid drivers' licenses or PennDot nondriver IDs. State officials downplayed that number, saying it was likely inflated by various factors, such as thousands of "inactive" voters on the rolls - people who had not voted in more than four years and likely had moved from Pennsylvania.
Oyler, who was called as a witness by the ACLU, acknowledged that more than 1 percent of Pennsylvanians lack the required ID. She also conceded under questioning by the plaintiffs' lawyers that if the law bars some people from voting, it would undermine the integrity of the electoral process. "Yes," Oyler testified, "indeed it would."
Under cross-examination by Senior Deputy Attorney General Patrick Cawley, she denied that any partisan motives figured in the decision to implement the new law this fall. "Absolutely not," she testified.
Critics of the law, including those suing to overturn it, have contended that the new voting requirements are part of a Republican strategy to help win Pennsylvania's crucial block of 20 electoral votes in November.
The ACLU and other critics have said those most affected by the law are the elderly, the poor, and racial minorities, many of whom traditionally vote for Democrats.
Barreto, the political scientist, said his survey found that those who are less educated, with lower incomes, or living in urban areas are more likely than other voters to lack proper ID.
The very young and the very old, as well as women, are less likely to have the correct ID, he added.
Also, Barreto testified, his survey found that a substantial portion of registered voters in the state - 34 percent - did not even know about the new law.
On cross-examination, Cawley asked Barreto if the state's aggressive public-education campaign, which includes a blitz of television, radio, and print ads explaining the law, would offset some of the problems Barreto had highlighted.
Barreto was skeptical. He testified that research suggests public-information campaigns in election years are often less effective than anticipated - and can lead some voters to draw incorrect conclusions.
"I do not believe there is enough time to change people's perceptions of the law," he said.
The hearings before Commonwealth Court Judge Robert Simpson continue Friday.
Contact Angela Couloumbis at 717-787-5934 or firstname.lastname@example.org, or follow on Twitter @AngelasInk.