U.S. ambassador to the United Nations Nikki Haley. U.S. officials in Geneva last week accused a U.N. representative of grossly exaggerating the amount of poverty in America. (Hector Retamal/AFP/Getty Images)

The Trump administration says the United Nations is overestimating the number of Americans in “extreme poverty” by about 18.25 million people, reflecting a stark disagreement about the extent of poverty in the nation and the resources needed to fight it.

In May, Philip G. Alston, special rapporteur on extreme poverty and human rights for the U.N., published a report saying 40 million Americans live in poverty and 18.5 million Americans live in extreme poverty.

But in a rebuke to that report on Friday, U.S. officials told the United Nations Human Rights Council there only appear to be approximately 250,000 Americans in extreme poverty, calling Alston's numbers “exaggerated.”

The rift highlights a long-running debate among academics over the most accurate way to describe poverty in America, one with enormous implications for U.S. policy-making and the nation's social safety net. It also sheds light on the ongoing feud between Trump and U.N. officials over Alston's report on American poverty, with U.S. Ambassador Nikki Haley last week calling the report “politically motivated” and arguing it “is patently ridiculous for the U.N. to examine poverty in America.”

But who is right about the number of Americans in extreme poverty?

It depends on how you define it.

The U.N.'s numbers come from the official Census definition that has been kept for decades by the U.S. government, defining extreme poverty as having an income lower than half the official poverty rate, Alston said in an interview. (For 2016, that was about $12,000 a year for a family of four.) By this criteria, the poverty rate in America has only slightly ticked downward since the mid-1960s.

The U.N. is using the Census figure that is “the gauge most people rely on when measuring extreme poverty,” said Mark Rank, a poverty expert at Washington University in St. Louis.

Some on the right have long rejected this measure in part since it only counts income, or how much money each American receives. Instead, American officials in Geneva cited survey data produced by the Heritage Foundation, a conservative think tank, that also measures purchasing power.

Citing a recent survey of American households, Heritage found only 0.08 percent of American households (or about to 250,000) are in “deep poverty,” defined by Heritage as living on less than $4 a day. This statistic does account for government social spending programs that help the poor — like Medicaid, food stamps, and housing assistance — while the figure cited by the U.N. does not.

“No one likes the official poverty measure because it doesn't count the enormous assistance we provide low-income Americans,” said Robert Doar, a conservative scholar at the American Enterprise Institute think tank. “It makes you think they have very little — that they have nothing — when in fact that's not true.”

Several poverty experts acknowledged flaws with the official Census count, but described the Heritage statistic cited by the U.S. as much too low. Some questioned why $4 a day was an appropriate measure of extreme poverty, since that only translates into about $1,500 of spending for an entire year on food, health care, rent and everything else needed to survive.

The Heritage number cited by the U.S. also does not reflect that many families must go into debt to sustain spending, and that government benefits like Medicaid and food stamps cannot be used to meet some unexpected expenses. Another criticism of Heritage's data is it is based on a survey of consumers that appears to produce different results than other poverty data, according to poverty experts.

“It's a total joke,” said Rank, the Washington University professor. “To say that there are 250,000 people in deep poverty in the U.S. is just ridiculous.”

Other estimates have come in lower than the official U.S. Census report but still significantly higher than the Trump team's estimates.

In response to concerns about the official poverty rate, the Census in 2009 created a “supplemental” poverty rate that does account for government benefits like food stamps. That number shows about 15.7 million Americans are in “deep poverty” in 2016, according to Gregory Acs, a poverty expert at the Urban Institute, a nonpartisan think tank.

Another convention for measuring poverty overall is to look at those with less than half the median national disposable income. By that measure, about 18 percent of Americans are in poverty — higher than that virtually all other developed nations, according to the Center on Budget and Policy Priorities.

A separate study from Princeton University economist Angus Deaton, also cited in the U.N. report, found about 5.3 million Americans live on less than $4 a day, including government transfers.

“No one is claiming that there are 18.5 million people below $4 a day,” Deaton said in an email. “It is hard to do this accurately, but I do think that using the [survey data] as Heritage does is certain to understate the problem.”

The U.S. response to the U.N. argued poverty in America has fallen by 77 percent “based on some measures of consumption” since 1980. Poverty experts say that is hard to square with the data.

“You can spend all day arguing about how many people are living on $2 a day vs. $4 a day,” said Kristin S. Seefeldt, of the School of Social Work at the University of Michigan. “But if you spend any amount of time in poor communities in the U.S., it's obvious there's still a lot of deprivation and 250,000 is a ridiculously low number.”