A study recently published in Science by four Australian scholars (myself, Professors L. Cameron and L. Gangadharan of Monash University and Associate Professor N. Erkal of University of Melbourne) suggests that individuals who grew up as single children as a result of the strict implementation of the family planning policy in 1979 are, on average, less trusting, less trustworthy, more risk-averse, less competitive, more pessimistic and less conscientious.

The research is based on data collected from economics experiments involving 421 people born in Beijing just before and just after the introduction of the family planning policy, under which most urban families are required to have only one child. The samples spread evenly across the (pre-policy) 1975, 1978, and (post-policy) 1980 and 1983 birth cohorts, with gender balance within the groups. Surveys to elicit personality traits were also used.

The behavioral consequence of not having siblings has been of interest in developmental psychology for many decades. It is believed that pro-social development is shaped by parents as well as through social interaction with peers, including siblings. The difference in relationships with parents and lack of interaction with siblings have been identified in psychology as two reasons for a single child to develop differently from those having siblings.