— A three-judge panel hearing a challenge to state legislative voting districts on Thursday struck much of the testimony of an expert brought in by Republican lawmakers, calling his review of various voting maps "not reliable."

Common Cause North Carolina alleges that state House and Senate district maps are were drawn illegally by the Republican-controlled General Assembly into gerrymandered districts that favor GOP candidates. The two-week trial is expected to wrap up on Friday.

Much of the trial has involved arcane testimony from statisticians, political science professors and other expert witnesses about hundreds of simulated elections, standard deviations and outliers as attorneys for Common Cause and state lawmakers spar over how much of a partisan advantage the House and Senate maps give to Republicans.

The maps were redrawn to eliminate racial gerrymanders courts found in maps drawn after the 2010 census, and Republican legislative leaders insisted that they didn't consider the race of voters at all in the new maps. But Common Cause has alleged that the maps are almost identical to ones drawn months earlier by longtime consultant Tom Hofeller that included voter racial data.

Hofeller died last year, and his estranged daughter turned many of his computer files over to Common Cause.

Republican lawmakers called on Douglas Johnson, the founder and president of National Demographics Corp., a California-based redistricting consultant, to rebut those claims, and Johnson testified Wednesday afternoon that his analysis showed a 36 percent difference between Hofeller's maps and the ones adopted by lawmakers.

Common Cause attorney Daniel Jacobson challenged that on Thursday morning, noting that Johnson didn't include close to a dozen House districts in his analysis that perfectly matched those drawn by Hofeller. Johnson also admitted under cross-examination that he sometimes included comparisons showing as little as 3 percent overlap while excluding others that showed more than 90 percent overlap.

"You reported specific numbers," Jacobson said. "Those numbers are completely wrong, right?"

"They apparently mismeasured the degree of the change. They don’t change the fact that there is significant change between the maps," Johnson replied. "Whether it’s 36 percent or, if I was off by half, it’s still 18 percent. It’s still one in five residents who were moved between the two maps."

"Sitting here today, you cannot tell the court that your numbers are correct, right?"

"I can tell the court that the basic idea is still true, that there is a significant population moved," Johnson said.

"I just want to be very clear. Sitting here today, you concede those numbers were wrong."

"Those exact numbers appear to be wrong. I would need to double-check that."

"Sitting here today, you have no idea what the correct numbers are."

"I know they’re somewhere between 36 [percent] and probably half that."

"When you say half that, you’re just speculating, right?"

"No," Johnson said. "The 36 percent is the average change in each of the districts. So if there are, as you say, 10 or 12 districts added to that, those numbers are going to swing that relative to shifting the average for all of the districts. It would make it smaller, but at most, you would cut it in half, and you’d still be at one in five people moved from the Hofeller plan and the enacted plan."

Johnson also said he needed to apologize to a spokesman for Senate President Pro Tem Phil Berger, who issued a news release last week claiming that maps drawn by Common Cause in 2017 were closer to Hofeller's maps than the ones lawmakers adopted.

Jacobson pointed out flaws in Johnson's calculations in that comparison as well.

"I just want to be clear, sitting here today, neither the court nor the public nor anyone else can rely on the overlap percentages that you calculated, right?" Jacobson asked.

"The specific numbers are off, but the conclusion remains true and factual, that there is a significant change," Johnson replied. "That’s just how averages work. If there’s 12 missing, they’re not going to overwhelmingly swing the numbers when there’s a lot more than 12 in the pool."

The judges weren't convinced, and Wake County Superior Court Judge Paul Ridgeway said that expert witnesses must base their opinions on reliable methods and principles.

"With respect to both the House and Senate maps, the principles used by Dr. Johnson were not reliable," Ridgeway said, "or the principles were not applied reliably in this case."

Sen. Harry Brown, R-Onslow, followed Johnson on the witness stand Thursday, with an attorney for Common Cause trying to pin him down on why he and other Republicans backed independent redistricting reforms when they were in the minority at the General Assembly but are shooting it down now that they’re in the majority and in control of the voting maps.

Attorney Steve Epstein repeatedly asked Brown why he co-sponsored bills in 2007 and 2009 to change the way maps are drawn and whether he believed at the time something had to be done to keep Democrats from rigging the maps. Brown wouldn’t answer yes or no, saying repeatedly that Republicans were mostly trying to make a point back then, knowing Democrats wouldn’t even give the bill a committee hearing.

"We knew this bill would never be heard," Brown said. "It was more to make a point at that time that we weren't happy with the districts."