THEY were known as China's "little emperors" – the offspring of one-child families born after the country's draconian family-planning policy was introduced in 1979.
They became the "spoilt generation" of teenagers who didn't experience the joys and heartache of sibling rivalry or share and share alike. At least that was the simplistic stereotype of the singleton children born in modern China, based on anecdote and hearsay.
But now, scientists have produced the first convincing evidence to suggest that the one-child generation of China has indeed become a rather maladjusted lot.
The one-child policy came about after a rapid growth in the population in the 1950s and 1960s. It was strictly enforced in urban areas.
Chinese authorities claimed the policy was a great success, preventing more than 250 million births between 1980 and 2000.
However, more than 30 years after it began, an unintended consequence has emerged; it has fundamentally changed the psychology of young Chinese men and women, according to scientists.
Children born after the policy have grown up to become less altruistic and trusting, more timid, less competitive, more pessimistic and less conscientious than those born just before the policy, they claim.
The study analysed the attitudes of young adults, using games designed by economists to test behaviour and attitudes, such as whether the subjects are likely to share something with a stranger or are ready to trust someone they don't know.
When the scientists compared two age groups born a few years before the policy was introduced with two age groups born just after, they were surprised to find such marked differences in the kind of personality traits which influence social relationships that could have important ramifications for China's future.
Lisa Cameron, of Monash University in Melbourne, Australia, said: "We find quite large impacts. Those who are the only children as a result of the policy are considerably less trusting, less trustworthy, more risk-averse, less competitive, more pessimistic, less conscientious and possibly more neurotic."
"Those born under the policy are less likely to be employed in risky occupations, such as self-employment, freelancing or the financial sector. So it may be that the one-child-policy generation will be less entrepreneurial."
The scientists asked the volunteers, now in their 20s and 30s, to carry out a series of economics games to test features of their personality, using real money as an incentive.
"Economic experiments have the advantage of allowing the researcher to observe particular, well-defined types of behaviour," Dr Cameron said.
"Experimental participants are also incentivised with money, the amount of which depends on the decision made in the experiment, which, experimental economists argue, provides a greater motivation for participants to reveal their true preferences."
What became clear, the scientists say in their study published in the journal 'Science', is that one-child offspring suffer from what they term "sibling deprivation", meaning that a lack of brothers or sisters appeared to make them more self-centred, less co-operative and less likely to get along with their peer group.
Previous work on one-child families in the West, where parents have largely chosen to have just one baby, have found little differences in behaviour between them and the offspring of larger families. What was different here was the ability to look at a whole society where parents were coerced into having no more than one child.
On paper, singleton children should have an advantage in that they have the full attention of their parents and do not have to compete with siblings.
But in practice, the findings suggest that singletons may have missed out on the rough and tumble and give and take of growing up with other children.
As one commentator noted: "Perhaps the biggest surprise of the study is how thoroughly the only-child subjects lived up to their bad reputation."