BEIJING — Chinese people cheering on their country’s ascent sometimes comfort themselves with the idea that Asia’s other behemoth, India, is years from surpassing China’s population and decades from emerging as a potential economic peer.
But Yi Fuxiang, a Chinese scientist based in Wisconsin, boldly challenged that assumption this week in Beijing. He laid out arguments that India may already be more populous than China, a view that has created a controversy about whose numbers to believe in forecasting China’s demographic and economic destiny.
“India could become the No. 1 country,” Mr. Yi, a medical expert and population researcher at the University of Wisconsin, Madison, said in an interview. “There are many reasons, but population is the most important one.”
China’s real population may be 1.29 billion people, 90 million fewer than the government’s estimate of 1.38 billion in 2016, Mr. Yi told a meeting at Peking University on Monday, citing what he said were telltale inconsistencies among birthrate, hospital and school statistics. India’s population, on the other hand, had grown to 1.33 billion in 2016, according to the United Nations.
“I want people to pay attention, because this is such a big issue for China,” Mr. Yi said. He has long criticized China’s family planning policies that emerged in the 1970s and took a draconian hold in the 1980s. “If so many aggregate numbers are wrong, so how can we make accurate predictions?”
Mr. Yi said that he was not just splitting statistical hairs. China’s birthrate will determine the size of the work force sustaining its economy, and the data indicated that stagnation could occur in coming decades, he said.
Chinese main official population statistics have often masked a steep falloff in the birthrate, Mr. Yi said. Even more sobering, he said, President Xi Jinping’s decision in 2015 to loosen the one child policy was too late and piecemeal to arrest a decline in birthrates, Mr. Yi said.
Family planning policies, sometimes enforced with sterilizations and abortions, have ended, but left a lasting imprint on policies and attitudes, Mr. Yi said.
“We enforced the one-child policy for over three decades, and a swathe of economic and social policies came to center on one child,” Mr. Yi said at Peking University, according to a Chinese transcript that he shared online.
“Even if family planning stopped, habits die hard,” he said. “Overall, our structure is where Japan was in 1992, and our economic waning will be a long-term trend.”
Other demographers strongly disagree with Mr. Yi.
His findings have not been published in a peer-reviewed journal. Some Chinese experts said that Mr. Yi overstated the problems in the official data, perhaps to fit his longstanding criticism of China’s family planning controls.
Some scoffed at the idea that China had essentially cooked data to create a phantom population almost as big as Henan Province, which has 94 million people.
“I think that the numbers from the National Bureau of Statistics are quite reliable,” said Lu Jiehua, a population researcher at Peking University, referring to the birthrate estimates.
“As well, what would their motive be for faking on a major scale?” Mr. Lu said. “Being totally dismissive is not objective or scientific.”
This debate has broad implications, but it will also be fought over seemingly slight differences in assumptions and data that population scientists use to study trends.
That is a difficult in any society, but in countries like China and India, which are plowing through tumultuous industrial and social changes, it’s even more difficult. And Chinese officials’ habit of massaging data to show their policies in the best light added distortions, Mr. Yi said.
China’s official birthrate — the average number of children born by each woman — is much lower than the rate given in state statistics, he said. China’s fertility rate in 2015 fell to 1.05 births per woman, far lower than the rate of up to 1.64 births per woman estimated by China’s National Health and Family Planning Commission, he said in a PowerPoint presentation at Peking University. The commission did not reply to questions faxed to them about Mr. Yi’s claims.
China’s demographic stagnation could be worse than Japan’s, he argued. Chinese women show less desire to have more than one child and China has not built a robust welfare net that can protect older Chinese.
“Young people don’t want to have one child, let alone two children,” he said. “In the future, it will be very hard to achieve an increase.”
But some demographers said Mr. Yi appeared to underestimate the ability of Chinese statisticians to reach reasonably accurate estimates.
“The numbers from the National Health and Family Planning Commission are derived from hospital childbirth statistics,” said Liu Hongyan, a researcher at the China Population and Development Research Center, a government institute in Beijing. “In recent years the rate of hospital births has been quite high, up to 97-98 percent, so I think those numbers from the hospitals are quite solid.”
In India, too, Mr. Yi’s findings were met with raised eyebrows.
K.S. James, a professor of population studies at Jawaharlal Nehru University in New Delhi, said it was unlikely that population estimates were so off that India had already overtaken China. That will happen in the coming years, he said.
Indian people born 20 years ago “will be getting married now,” Mr. James said. “The population will grow for the next 30 to 40 years.”