The new only-child generation grew up to be less trusting, more risk-averse, less competitive, more pessimistic, less conscientious, and it appears, more neurotic.

Jason Lee/Reuters

PROBLEM: China's one-child policy, introduced in 1979 and strictly enforced, succeeded in slowing population growth. The first of the children who were born -- one per family, under threat of heavy penalties and by means, for some, of forced sterilization -- are now fully grown. What does it mean, for them and for China, that an entire generation grew up without siblings?

METHODOLOGY: Researchers at a university in Australia seized on the natural experiment created by the Chinese government, recruiting thirtysomethings from Beijing who had been born before and after the one-child policy was implemented. The study had a small sample size, of about 421 participants, that nonetheless marked a large change in demographics. Despite being close in age, they were from vastly different generations, from those who were born in 1975, when only about a quarter of Chinese families had only children, to those born in 1983, where the number rose to 91 percent.

The participants played a variety of "Deal or No Deal" style econ games designed to test behaviors and attitudes with real-world social and economic correlations.

RESULTS: Compared to children born right before the one-child policy was implemented, children born under its jurisdiction scored lower on a whole spectrum of measures: They grew up to be less trusting, more risk-averse, less competitive, more pessimistic, less conscientious, and it appeared, more neurotic.