China's one-child policy impact analysed
People growing up under China's one-child policy are less trusting, more risk averse and more pessimistic, a study concludes.
An Australian team of researchers compared people who were born just before the policy was introduced with those born after.
They used economic games and surveys to assess the participants' behavioural and personality traits.
The findings are published in the journal Science.
The lead author of the study Professor Lisa Cameron, from Monash University in Victoria, told the BBC's Science in Action programme: "We found that people born under the one-child policy were significantly less trusting and less trustworthy, significantly less likely to take risks and less competitive than those who were born before.
"We also conducted personality surveys and we found that those born under the one-child policy were less conscientious, slightly more neurotic and significantly more pessimistic than those born before."
However, another scientist from the University of Oxford said that the team was making a very strong claim and the differences between the two groups might not be solely down to the policy.
China's population-control policy was introduced in 1979, and it restricts couples in urban areas to have only one child.
The researchers looked at 421 adults: half were born a few years before the policy was introduced and the other half were born a few years after.
They used different economic experiments to study the participants.
One, called the "trust game", involved a scenario where a volunteer was given some money. They were then given the option of giving some of this to an anonymous partner, who in turn would get that amount tripled. The anonymous partner then had the option of giving back some of this to the original volunteer.
Professor Xin Meng, from the Australian National University in Canberra, explained: "The first part of this is about trust. It says I trust the other person will return some money. The second is about trustworthiness, that somebody trusted you to return the money.
"Those who were born after the policy would give significantly less money to the partner, and they also returned less money to the original person who gave them the money."
Other simple experiments and surveys tested other traits such as the propensity for taking risks, competitiveness, optimism and pessimism.
Prof Meng said: "In China, there is a very common belief that the one-child generation is spoilt and selfish and they are not hardworking…. even though it is a common belief, no-one has ever tested this thing, or given hard evidence - and that is why we decided to study this."
She added that China was currently reconsidering its policy, and she hoped the results of the study would be taken into account.
The researchers said that their results were not representative of all children who grew up without any siblings.
Prof Meng explained: "In other societies where fertility is a choice, only certain types of people choose to give birth to a single child - the majority will not. And these people will have certain personality traits and behaviour patterns. And when they give birth to a single child, these children are more likely to inherit these traits.
"When you look at a society where fertility is a free choice, then the results will be a combination of the qualities you inherited, plus those you have gained growing up as a single child."
The team added that the one child policy was not strictly enforced throughout the country, so the results should not be applied to everyone in China.
Prof Cameron explained: "I am conscious when I present these results that I am standing up there talking about a slew of what people might think as negative consequences of the policy on only children.
"I certainly don't want to portray that only children have significant problems. It is just suggestive that growing up without siblings does have an impact."
Professor Stuart West, from the University of Oxford, said the study was "very interesting".
However, he cautioned against some of the conclusions that had been drawn.
He explained: "They are making very strong claims about differences in behaviour for people born before or after 1979, and they are inferring it is all to do with the introduction of the one child policy in that year.
"The problem is that is a potential explanation for that data - but there are almost an infinite number of other explanations of anything else that could have varied with time: variation of socio-economic environment, prosperity, nutrition, political environment - anything."