Is New York City’s ‘Remarkable Growth Story’ Ending?

There are 8.4 million people in the Naked City. This is the story of 40,000 of them — the number of people the Census Bureau estimates that New York City lost last year.

The loss suggests that New York’s robust post-recession expansion since 2010 has finally slowed, halting what the city’s leading demographer had called a “remarkable growth story.”

But city officials disputed the Census Bureau’s findings, calling them “tenuous” at best. They said New York’s population may not have fallen, and suggested that the census numbers may be skewed, in part, because of a change in the survey’s methodology.

“Our team is very much questioning those results and the methodology that was used,” Mayor Bill de Blasio said. “Every indicator we have seen in recent years is of steady growth.”

At stake is more than simply bragging rights: Next year’s decennial census, which is supposed to count everyone in the country, will determine the size of the New York congressional delegation and the distribution of billions of dollars in federal aid. The city is projected to lose two seats in the House of Representatives after the 2020 count.

The estimated decline, to 8,398,748 from a record 8,438,271 in 2017, covers the year ending on July 1, 2018. It amounts to 39,523 New Yorkers, or fewer than live in Co-op City in the Bronx.

The loss breaks down to 18,000 in Queens, 13,500 in Brooklyn, 7,500 in the Bronx and 1,000 in Manhattan. Staten Island recorded a gain of 663.

The latest figures suggest that population shifts in New York reverted to what had been a conventional pattern: Typically, more New Yorkers move to other parts of the United States than come from elsewhere in the country. But immigration from abroad usually makes up that loss, and tends to push the city’s population higher.

This time, 137,000 more New Yorkers left the city for other parts of the country — retiring or moving to less expensive cities in the Sun Belt — than arrived from someplace else in the United States. The net increase in international migration was only about 49,000.

Joseph J. Salvo, the chief demographer for the Department of City Planning, acknowledged that the rate of population growth in the city has slackened, but challenged the latest estimate’s bottom line.

“There is a very real possibility that the population did not decline,” he said on Thursday. “We think the population is higher than 8.4 million.”

One reason, he said, is the change in methodology meant to make one of the American Community Survey questions less ambiguous. Instead of asking people born abroad when they arrived in the United States, the bureau based its latest count on a more specific question: It asked where they lived a year ago.

“Our feeling is that the number for net international migration is likely too low because the new method tends to produce a lower figure,” Dr. Salvo said.

He said the new method, while more conservative, may prove to be more accurate.

“The estimation methodology for net international migration has changed significantly, resulting in a revised 2010-2017 international migration estimate that is 31 percent lower than the previous vintage,” a Planning Department analysis said.

“While the previous vintage estimated international net migration for the city at 624,000,” the analysis added, “the latest vintage provides a lower estimate of 431,000 over the same period, which are likely too low.”

“The Census Bureau’s methodology is not robust enough to precisely quantify the magnitude of these year-to-year changes,” the City Planning Department’s analysis of the latest estimate said.

In the year ending July 1, 2017, every borough recorded growth. The Bronx recorded the largest increase of any New York State county, up 6.2 percent.

Even under the adjusted method, since the 2010 census the city gained 223,000 residents, or 2.7 percent — about 27,000 people annually.

A net loss of 768,000 through domestic migration was offset by a net gain of 480,000 immigrants from abroad and by more births than deaths.

“I would say to all New Yorkers that what we see with our own eyes appears to be the real truth — that our population has been steadily growing,” the mayor said. “I’m sure there’s some outflow, but from everything I’m seeing it’s being more than made up for by the inflow.”

The New York metropolitan area, which includes parts of New Jersey and Pennsylvania, remained the nation’s most populous. It recorded a slight decline to 19,979,000 people.

An analysis by William H. Frey, a senior fellow at the Brookings Institution’s Metropolitan Policy Program, found that population losses in the region were driven by the decline in the city, as New Yorkers moved away from the metropolitan area entirely.