The ads, which target Democrat Beverly Perdue, say that North Carolina has "the largest-growing tax burden in the country." The RGA told Dome that it based the claim on this April 12, 2007 article from The Tax Foundation.
According to the article, North Carolina's state-local tax burden jumped from 36th highest in 2000 to 19th highest in 2007 – "the largest increase of any state."
But this chart (pdf) from The Tax Foundation says that since 2000 North Carolina's rank has fluctuated between 17th and 22nd. In 2008, it is 20th.
The Tax Foundation told Dome Tuesday that it has changed its methodology since the 2007 article. The article used the old methodology, which the foundation considers less accurate than its new methodology, said Gerald Prante, an economist with the foundation.
Prante said the new methodology does a better job accounting for out-of-state taxpayers, among other things. "It's changed, just searching for what the truth is, trying to get the best estimate possible," he said.
Foundation spokesman Matt Moon apologized for the confusion. "That's very much our bad," he said.
The new methodology has been the subject of some criticism from another tax policy group that is more liberal.
The RGA has not said whether it will now change the ad.