The United States Supreme Court has heard oral arguments about the legality of a move by the Trump administration to add a citizenship question to the U.S. census.

The White House has argued that adding the question is within its authority and will aid the federal government in enforcing the Voting Rights Act.

Opponents of the move call that justification a ruse, arguing that the intent and effect of adding a citizenship question will be to discourage certain populations — namely, immigrants and Latinos — from answering the census.

And that, opponents argue, will lead to those populations and the counties and states in which they live being underrepresented — not just in Congress, but also in terms of hundreds of billions in federal dollars.

Overall, more than half a trillion dollars of federal funding go to the states annually via more than a dozen major federal programs informed by the census, according to The George Washington Institute for Public Policy’s “Counting for Dollars 2020” project.

Massachusetts received approximately $16 billion in federal aid from major programs tied to the census in 2015, the most recent year for which the project is able to give estimates.

While it’s a fraction of all federal funding, Massachusetts received significantly more on a per capita basis — about $2,370 per resident — than the national average of about $1,840 per U.S. resident.

If the addition of a citizenship question to the census did suppress response, how exactly might that affect funding apportioned to the Commonwealth?

The short answer: No one is sure. But there are some ways to at least begin answering the question.

Read More: How Would A Citizenship Question On The 2020 Census Affect Massachusetts?

1. With higher immigrant populations, Massachusetts could be subject to under-counting
Immigrants make up about 17 percent of Massachusetts residents — more than double the national average of 7 percent. Just over half (about 52 percent) of all Massachusetts immigrants are naturalized citizens, and about one-fifth of Massachusetts immigrants identify as Latino.

The state’s foreign-born population is growing and, according to U.S. census data, is overwhelmingly the driving force behind overall population growth in Massachusetts. Without the growing immigrant population, the state’s head count would be shrinking.

Opponents of the citizenship question say these populations — immigrants and Latinos — are more likely to be under-counted if a citizenship question is added to the census.

There is some evidence to back up that claim, including a recent study commissioned by the U.S. census itself, which found that a citizenship question was a “major barrier” to some surveyed, especially for Spanish-speaking and immigrant respondents.

Census officials have elsewhere estimated that a citizenship question could cause a decline in self-reported responses by non-citizens of nearly 6 percent or more.

2. Massachusetts’ largest source of federal funds — Medicaid payments — appear insulated
As is true nationally, the bulk of federal funds apportioned to Massachusetts tied to the census come from the federal Medicaid program, which partially reimburses states for state Medicaid spending.

In 2015, Massachusetts received about $9.3 billion in Medicaid reimbursements, more than half of the $16 billion the state received in overall federal funding related to the census.

That funding is tied first and foremost not to the census count, but to state Medicaid spending.

Under the Affordable Care Act, states receive more funding for Medicaid if they spend more on their own Medicaid programs. As a state that spends a lot on its Medicaid program, MassHealth, Massachusetts receives substantial federal support.

But the rate at which the state’s spending is reimbursed is tied to measures of the relative wealth of a state’s residents — figures that ultimately come from the census.

“The idea is that wealthier states like Massachusetts … get less back, on the dollar, than poorer states like Louisiana,” says George Washington University Professor of Public Policy Andrew Reamer, who directs the “Counting for Dollars 2020” project.

Under-counting less-wealthy residents, Reamer says, could make a state seem wealthier than it is — triggering lower reimbursement rates.

But as a relatively wealthy state, Massachusetts already receives the legally-mandated minimum Medicaid reimbursement rate of 50 cents on the dollar, Reamer says. Unless Massachusetts’ place among other states in terms of wealth were to change significantly, he adds, it’s unlikely that rate would change.

3. Programs for children and housing would be more vulnerable
Other programs, however, could be significantly more vulnerable to under-counting of immigrant and Latino populations.

Among those programs: School lunch and nutrition programs for children from low-income families, food and nutrition programs for pregnant women, and housing assistance programs for low-income residents.

Nancy Wagman, of the left-leaning group Massbudget, says it’s difficult to know how many people could be affected by the addition of the proposed citizenship question. However, she adds, any under-counting of immigrant populations — especially immigrant populations that are growing — could have a significant effect on the billions of dollars in federal funds that are largely assisting those groups.

And it’s happened before: Reports by the Census Bureau estimate that Massachusetts children aged five and younger were under-counted in the 2010 census by about 20,000 children.

4. Hard to count areas
According to the Census Bureau, about 23 percent of Massachusetts residents — one in four — live in what the census terms “hard-to-count” areas — neighborhoods or census tracts with historically low rates of return for the census survey.

Those areas are disproportionately concentrated in Massachusetts cities — including not just Boston, but “gateway” cities with especially high immigrant populations, like Lawrence and Fall River.

“Even without the citizenship question, we would be looking at a very challenging 2020 census,” says Eva Millona, executive director of the Massachusetts Immigrant and Refugee Coalition, which has vigorously opposed a citizenship question.

“But the question will make it many times harder,” says Millona. “So we are very, very worried, in particular given the large number of foreign-born here in our commonwealth. This will translate into costing out cities millions of dollars, and possibly costing us a congressional seat.”

5. The big picture
Federal dollars come to Massachusetts and other states via more than a dozen major programs, whose funding is determined to varying degrees by the census. It’s almost impossible to know exactly how the effects of a citizenship question would alter the flow of those hundreds of billions of dollars.

But, says Reamer, it is less difficult to generalize about how the under-counting of specific populations would affect the overall picture of federal funding nationwide.

This article has been updated.