UPDATED: Who pays taxes? Roberton Williams knows

On the Sept. 18, 2012, edition of PBS "NewsHour," anchor Judy Woodruff explored Mitt Romney’s statement about 47 percent of Americans not paying taxes in part by noting relevant research.

Woodruff said Romney's reference to the 47 percent who pay no federal income taxes draws roughly on data from the nonpartisan Tax Policy Center, adding that the Washington-based group's analysis further shows more than a quarter of Americans pay payroll taxes without incurring income tax liability. Others paying no federal income tax include some elderly people on Social Security as well as households earning under $20,000 a year.

The center’s tax expert, Roberton Williams, who also took questions from Woodruff, is familiar to us. He ranks among  experts who we often consult when checking claims about taxes and spending.

Primed for a Williams' refresher? We’ve compiled some PolitiFact checks drawing on Williams to the right -- including our review of a claim by Texas U.S. Rep. Lamar Smith and a just-completed verification of Romney’s statement by PolitiFact in Washington.

Clarification, 4:20 pm, Nov. 29, 2012: Thanks to a reader's inquiry, we amended this story to clarify that every elderly recipient of Social Security should not be assumed to be paying no federal income tax.