WASHINGTON — When she speaks about poverty and inequality on the campaign trail, Hillary Clinton often mentions one plan that stands out in its simplicity: Rep. Jim Clyburn's "10-20-30" formula.

The concept championed by the South Carolina Democrat is simple: steering 10 percent of federal investments to neighborhoods where 20 percent of the population has been living below the poverty line for 30 years.

Clyburn, the third-ranking Democrat in the House of Representatives, said that he discussed the plan with Clinton when she was in Charleston for a Democratic presidential debate last January. Since then, she has often brought it up on the stump.

"I'm a big fan of Congressman Jim Clyburn's 10-20-30 plan," she said last week in a speech at the joint National Association of Black Journalists and National Association of Hispanic Journalists conference in Washington. "We need that kind of focused, targeted investment in urban places wherever Americans have been left out and left behind."

She also praised Clyburn's plan, which has been adopted by the Congressional Black Caucus, in her July speech at the NAACP conference, saying that as president she would expand it as part of her push to invest in infrastructure.

"Ultimately, reversing the legacy of racism and underinvestment will require directing more federal resources to those who need them most," Clinton wrote in an opinion piece in Ebony magazine. "I believe the 10-20-30 model holds promise and this principle should be expanded to other programs."

Although Clinton tends to bring it up when speaking to black audiences, Clyburn is emphatic that the power of the formula approach is that it is impartial.

Some poverty initiatives direct their funds based on proposals and panels that evaluate a slew of different criteria, he said, and the sophistication of the system can pass over the poorest communities if they are not politically relevant or lack strong advocates.

Not so with the 10-20-30 plan.

"It is as straightforward as anything I've ever been involved in," Clyburn said. "My whole thing is if you're looking at fighting poverty, and you have a definition looking you in the face that has been there for generations — and I do mean generations — why not use that? It's not like anybody can accuse you of playing favorites."

Since his concept is based on statistics, it also puts it above partisanship, Clyburn said.

"Two-thirds of those counties are represented by Republicans, so it's not something I am pursuing as a partisan matter," he said. "And this formula applies as much to Latinos and Native Americans as whites."

Matt Freedman, a professor of economics at the University of California, Irvine, said that based on his reading of Clyburn's plan it could affect 20 million to 30 million people nationwide. These persistent-poverty communities are mainly clustered in the Deep South, Appalachia and on Native American reservations.

"The structure of 10-20-30 is very straightforward and easy to understand by both policymakers and the public," he said in an interview.

While a number of government programs already use similar formulas to determine where to send federal dollars, according to some economists they aren't the most efficient way to help as many people as possible.

"It does ensure a degree of objectivity and removes any partisan wrangling about where funds should go," Freedman said. "But in a sense it also ties the hands of policymakers and precludes them from putting the funds to the best possible use."

A community that just barely misses the criteria could miss out on funding that would have a quicker, deeper effect, he said.

"Some may be marginal communities on the wrong side of the threshold, where even just a little bit of extra help would have been key to getting them on a good trajectory," Freedman said. "In some of these isolated areas that are really persistently poor, the amount of dollars we're talking about (through Clyburn's plan) are nowhere near what would be needed."