Our experimental results show that people who are single children because of the family planning policy are likely to be less trusting, less trustworthy, more risk-averse, and less competitive. The post-experiment survey also shows that they are less likely to be optimistic and conscientious.

Some may challenge the findings, arguing that 421 observations cannot represent the cohorts of Beijing residents we are trying to represent and the findings from Beijing cannot be extended to other cities.

In statistics, the sample representativeness comes from randomness of the sampling. Conditional on random sampling the smaller the sample, the less likely it is to get statistically significant results. But the fact that we could get statistically meaningful results with 400 samples suggests that the results will be more significant with a larger sample size. We have described our sampling method in the Science paper in great detail, and we believe that our sampling strategy will ensure skeptics that our sample selection was indeed random.

We chose Beijing for our study because it is a city where the family planning policy was (and is still being) enforced most strictly. Thus, use Beijing allows us to get a cleaner "one-child policy" effect. We understand that Beijing is much richer than other cities. In the study, we did controls for education levels, which are often used as proxy for family income, and current family income levels, but they did not affect our results.

We also would like to stress that although relative to the pre-family planning policy cohorts the post cohorts are significantly less likely to have pro-social behavior, less risk-loving and less competitive, this does not necessarily imply that Chinese on average are less pro-social, less risk-loving and less competitive.

After all, currently the size of rural hukou (house registration) population, the majority of who didn't grow up as single children, is twice as large as the urban population. Among the group born after 1980, the urban hukou population is only one-fourth of the rural population. Our finding is confined to people with urban hukou, which may not be regarded as "average" Chinese. Furthermore, even compare urban post family planning policy generation with their counterparts in other countries, we still cannot conclude that Chinese are relatively less pro-social, more risk-averse and less competitive.

In fact, there is evidence to suggest that relative to people in other countries, Chinese on average are more trusting. For example, based on the 2007 World Value Survey, an article in The Wall Street Journal said 49 percent of the surveyed Chinese citizens believed "most people can be trusted" compared with 39 percent in the US.

Traditional Chinese culture is very altruistic and family oriented. It has always regarded hard work as a virtue. Traditions going back to thousands of year are not easily wiped out. However, the fact that our study has revealed that the strict family planning policy has significantly changed pro-social behavior of China's younger generation is alarming. We sincerely hope that the Chinese government will take into account our findings when considering whether to relax the family planning policy. Otherwise, overtime, it may have significant ramifications for Chinese society.

The author is a professor of economics at Australian National University, Canberra. The article is based on her essay and interview with China Daily's Zhu Ping.

(China Daily 01/28/2013 page9)