BEIJING — They’re called “little emperors” — the children born in China under a law that generally limits urban families to having just one child.

They grow up as the sole focus of doting parents. How does this affect them? What does it mean to Chinese society if generations of kids are raised this way?

Concerns about the “only child” practice in China have been expressed before. Now researchers present new evidence that these children are less trusting, less competitive, more pessimistic, less conscientious and more risk-averse than people born before the policy was implemented.

The study’s authors say the one-child policy has significant ramifications for Chinese society, leading to less risk-taking in the labor market and possibly fewer entrepreneurs.

“Trust is really important, not just social interactions but in terms of negotiations in business, working with colleagues in business, negotiating between firms,” said one of the authors, Lisa Cameron. “If we have lower levels of trust, that could make these kinds of negotiations and interactions more difficult.”

China introduced its family planning policy in 1979 to curb a surging population. It limits most urban couples to one child.

The new work by Cameron of Monash University in Australia and co-authors is published online today in the journal Science. The researchers said the results don’t necessarily apply to children born outside of the situation they studied: modern-day, urban China.

They recruited 421 Beijing men and women who were born within an eight-year period that included dates just before and just after the policy took effect in 1979. About 27 percent of the participants born in 1975 were the only child in their families, rising to 82 percent of those born in 1980 and 91 percent of those born in 1983. Researchers said the sample was better educated than the general population of Beijing but otherwise similar.

They administered tests to measure their altruism, trust, trustworthiness, risk attitudes and competitiveness, and gave them personality surveys. Cameron said the participants’ ages and views on ideological changes in China didn’t appear to affect the results.

The findings — including indications that those in the study were more sensitive and nervous — are no surprise, said Zou Hong of the School of Psychology at Beijing Normal University, who was not involved in the research.

“Only children in Chinese families are loved and given almost everything by their families and they can get resources at home without competition,” she said. “Once they enter society, they are no different from other people. Having been overly protected, they feel a sense of loss and show less competitiveness.”

Zou said parents of an only child tend to become overly nervous, when they are ill, for example, and “that feeling will be passed on to the children and make them become more sensitive and nervous.”

The Chinese government credits the one-child policy with preventing hundreds of millions of births and helping lift countless families out of poverty. But the strict limits have led to forced abortions and sterilizations, even though such measures are illegal. Couples who flout the rules face hefty fines, seizure of their property and loss of their jobs.

Last year, a government think tank urged China’s leaders to start phasing out the policy and allow two children for every family by 2015, saying the country had paid a “huge political and social cost.” It said the policy had resulted in social conflict, high administrative costs and led indirectly to a long-term gender imbalance because of illegal abortions of female fetuses and the infanticide of baby girls by parents who cling to a traditional preference for a son.

The researchers in Australia noted that children born long after 1979 will have grown up with very limited extended family and in a society dominated by those born into one-child families. So the psychological effects of the one-child policy “would, if anything, be magnified,” they wrote.

Toni Falbo, a professor of educational psychology at the University of Texas in Austin who studies these children, was puzzled that the study’s findings showed poor performance so consistently in virtually all measures. She said she would have expected a more mixed picture, and she hopes follow-up research is done.

In any case, there’s no reason to think that the results would be similar for children in the United States, she said. In China the only child grows up with different expectations, Falbo said, with Chinese authorities emphasizing that “these kids have to be the best possible. Most Americans want their kid to be happy; they’re not aiming for a world-class child of some sort.”

Careful studies done elsewhere that look for certain qualities in the only child find that “on average, they’re pretty much like everybody else,” she said.