Research by four Australian scholars claims China's family planning policy has had behavioral impacts on the generation of single children, saying such children tend to be less trusting, less trustworthy, and more risk-averse and pessimistic. The study also claims that such personal traits have implications for China's labor market and social development.

But a closer analysis of the study suggests the researchers might have jumped to a hasty conclusion. First, the sample size for the study, "Little Emperors: Behavioral Impacts of China's One-Child Policy", is too small to present the whole picture. The study covered 421 well-educated Beijing residents born between 1975 and 1983, with half of them being born before the implementation of the family planning policy in 1979 and the other half after.

The sample size is not big enough to account for the whole of Beijing, let alone China. Also, the rate of higher education among single children born in Beijing between 1980 and 1983 is not quite high; it was even lower on the national level.

Second, the study wrongly takes 1979 as a strict baseline for the enforcement of the family planning policy, because that was not the case. Such a policy was already in force in some parts of China. In 1979, it only became stricter and was extended throughout the country.

The subjects chosen for the study were between 30 and 38 years old today. But people in this age group cannot represent the massive population of single children below 30 years of age who grew up during a special time when Chinese society was transforming from collectivism to individualism.

Third, the two model groups of the research are not a cohort. The subjects born between 1975 and 1978 would now be 35 to 38 years old, and those born between 1980 and 1983 would be 30 to 33 years. Since the subjects from the two groups can differ because of the time interval of about four to seven years, the means do not serve the goals.

A span of four to seven years could see enormous changes in values, personalities and behavioral traits of a person, for example, if we were to compare the behavioral traits of a high school student with those of a college graduate. Four to seven years can exercise a lot of influence on a person's pro-social behavior.

In Yicheng county, Shanxi province of China, for example, many couples refused to use a pilot policy to have a second child. Given this development, if we compare cohort subjects from adjacent non-pilot counties with similar living standards, then the findings would be statistically more scientific than a non-cohort one that spans from four to seven years. The possible sampling suggestions are three: single children from the pilot county, children who grew up with siblings from that area, and single children from adjacent non-pilot counties.

The Australian researchers have admitted to have eliminated the "selection bias" of some parents choosing to have one child despite being conditioned to have more. Thus the comparison between single children with those who grew up with siblings is likely to be a combination of the differences in personality and behavioral traits, as well as the effects of some traits inherited from parents whose initial fertility decision was to have one child.