The courts have yet to issue their final word on whether the Trump administration can add a citizenship question to the 2020 census.

But starting Thursday, the Census Bureau is asking about a quarter-million households in the U.S. to fill out questionnaires that include the question, "Is this person a citizen of the United States?"

The forms are part of a last-minute, nine-week experiment the federal government is using to gauge how the public could react next year to census forms with the potential census question.

Around 480,000 households in most parts of the U.S., except Puerto Rico and remote Alaska, have been randomly selected to complete one of two versions of a test census form — one with the citizenship question, the other without.

The results, expected to be available this fall, will inform the bureau's upcoming advertising campaign for the 2020 census and plans for hiring people to visit households that don't respond to the census. Test participants would still have to complete forms for next year's actual head count.

The bureau usually conducts similar field tests before making any changes to census forms. But Commerce Secretary Wilbur Ross, who oversees the Census Bureau, approved adding the question before the bureau could test it on a form with the planned 2020 census questions. The lack of testing was among the "smorgasbord" of administrative law violations that a federal judge in New York cited in his ruling to block plans for the question.

"There is a great deal of evidence that even small changes in survey question order, wording, and instructions can have significant, and often unexpected, consequences for the rate, quality, and truthfulness of response," six former Census Bureau directors wrote in a 2018 letter expressing concern about the citizenship question.

Previously released research by the Census Bureau suggests the citizenship question is highly likely to scare households with noncitizens from taking part in the constitutionally mandated head count of every person living in the U.S.

The bureau declined NPR's request for an interview about what it's calling the 2019 Census Test, first announced late last year.

But in a written statement, the bureau's spokesperson, Michael Cook, said the test will allow the bureau to "fine-tune" its plans for the 2020 census.

"As a federal statistical agency, it is important to maintain a neutral testing environment so we are limiting certain details about the 2019 Census Test," Cook said.

The test's rollout comes as the wait continues for a Supreme Court ruling on whether the Trump administration can proceed with adding a citizenship question.

The administration says it wants to include the question to better protect the voting rights of racial minorities. But plaintiffs in one of the New York-based lawsuits over the question argue that administration officials have been concealing the real reason for the question. They allege that the documents of a GOP redistricting strategist show that the administration was driven to use the question to politically benefit Republicans and non-Hispanic white people when new voting districts are drawn.

In a filing released Wednesday, advocacy groups asked the Supreme Court to delay issuing that ruling because of the recently uncovered documents.

However, and whenever, the high court rules, the bureau will continue collecting responses for the census test by paper, online or over the phone through Aug. 15.

"The Census Bureau considers the information it will reveal to be valuable," the bureau said in a written response to calls to postpone the test from the National Association of Latino Elected and Appointed Officials and the Asian Americans Advancing Justice.

The timing of the census test risks setting up an awkward situation that could pose a public relations problem for the bureau. The Supreme Court could rule that the 2020 census cannot include a citizenship question while the Census Bureau continues asking around 240,000 households to complete test census forms with that question.

"This test represents, I think, a Hail Mary pass," says Terri Ann Lowenthal, a former staff director of the House oversight subcommittee for the census who now consults on census issues.

Lowenthal, who has spoken out against the citizenship question, says it is "highly unusual" for the bureau to carry out this test so close to the official start of the national head count. The 2020 census is set to begin in January in the most remote parts of Alaska, and most U.S. households can start participating in mid-March.

"It tells me that the Census Bureau is greatly concerned about the potential consequences of a citizenship question on census operations," Lowenthal says.

A 2018 national study by the bureau found the question to be a "major barrier" to participation in the head count by every household in the country. That could have long-term implications on census numbers used to determine how many congressional seats and Electoral College votes each state receives, as well as to draw new voting districts after the head count. Census data also guide how an estimated $880 billion a year in federal funding are distributed for schools, roads and other public services.

Unlike for the 2020 census, households that do not immediately return a completed census test form will not receive in-person visits from census workers, although the bureau is planning to send reminder postcards.

Still, the Coalition for Humane Immigrant Rights of Los Angeles and other immigrant advocate groups are expecting the test to touch off anxieties within immigrant communities.

"A lot of our community members quite honestly have never seen the census form or have never filled it out," says Esperanza Guevara, manager of CHIRLA's census outreach campaign.

Guevara says she and her colleagues are encouraging people to participate in the census, regardless of whether it includes a citizenship question. They emphasize that federal law prohibits the Census Bureau from releasing census responses identifying individuals until 72 years after they're collected.

"There's still some hesitancy sometimes in our community given that the Trump administration is certainly a wild card in a lot of senses and has been no friend of the immigrant community," Guevara adds.

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