Romney’s statistic accurately approximates the percentage of US households that do not pay federal income taxes. But he went on to suggest that this 47 percent relies on government help and refuses to “take personal responsibility” — an assertion that ignores the fact that most of these households pay payroll taxes for Social Security and Medicare and some are service members in combat zones.

Almost every American adult pays some combination of excise, property, sales, and state or local income taxes.

And contrary to Romney’s assertion that these are “people who will vote for the president no matter what,” many Americans who pay no federal income taxes are members of important Republican voting blocs — including seniors and residents of the Bible Belt.

“It’s empirically not accurate,” said John G. Geer, a political science professor at Vanderbilt University. “There are plenty of people who don’t pay federal income taxes who will support him, but he was trying to appeal to the folks in the room.”

Romney was filmed without his knowledge during a $50,000-per-plate dinner in Boca Raton, Fla., on May 17. The liberal magazine Mother Jones obtained footage of the event, posted excerpts and part of the video on its website on Monday, and released the full video of Romney’s remarks on Tuesday.

“There are 47 percent who are with [President Obama], who are dependent upon government, who believe that they are victims, who believe the government has a responsibility to care for them, who believe that they are entitled to health care, to food, to housing, to you-name-it,” Romney said at the fund-raiser, hosted by private equity manager Marc Leder.

Romney said his “job is not to worry about those people” in his effort to secure votes, adding, “I’ll never convince them they should take personal responsibility and care for their lives.”

Research by the nonpartisan Tax Foundation showed that in 2008, the states with the highest percentages of tax filers who did not pay federal income taxes were Mississippi, Arkansas, Georgia, Alabama, South Carolina, New Mexico, Florida, Idaho, Louisiana, and Texas. Obama won Florida and New Mexico but lost the other eight.

Some of the country’s poorest regions are Republican strongholds. Patchwork Nation — a collaborative research project of the Wall Street Journal, Christian Science Monitor, PBS NewsHour, WNYC Radio, and the Jefferson Institute — analyzed county-by-county voting patterns in the last three presidential elections and found overwhelming GOP support in places characterized by low incomes and high populations of service industry and agricultural workers and evangelical Christians.

“Romney seems to have contempt not just for the Democrats who oppose him, but for tens of millions who intend to vote for him,” William Kristol, editor of the conservative Weekly Standard, wrote in a blog post Tuesday.

In 2008, Obama captured large majorities of the very poor: 73 percent of voters with family incomes under $15,000 and 60 percent of those between $15,000 and $30,000, according to exit polling by The New York Times. But among voters whose family income was between $30,000 and $50,000 in 2008 — many of whom would have been exempt from federal income taxes — Obama won 55 percent of the vote, only two percentage points higher than among the general population.

Romney’s 47 percent figure appears to have been derived from a highly publicized study last year by the nonpartisan Tax Policy Center, which estimated that 46.4 percent of American households would pay no federal income taxes in 2011. That study was published three months after a report by Congress’s Joint Committee on Taxation showed that in 2009, 51 percent of households did not pay federal income taxes.

But the study by the center, a joint initiative of the Brookings Institution and the Urban Institute, did not support Romney’s suggestion that almost half the country is made up of people who do not take responsibility for their own lives and instead rely on government handouts.

“It’s really become a mantra on the right, that all these people don’t pay taxes, but Romney missed the mark in his description,” said Eric Toder, a Tax Policy Center codirector.