Testing the Only-Child Advantage in Cognitive Development in the Context of China’s One-Child Policy

Using data from a recent national survey of approximately 20,000 Chinese middle school students, we tested the difference in cognitive development between only-children and children with siblings using non-parametric matching method. We took advantage of the massive increase in involuntary only-child families in China under the one-child family planning policy (1979–2015) to reduce the bias introduced by the otherwise pervasive human tendency to avoid having only one child. Our average treatment effect for the treated estimates indicates no significant cognitive difference between only-children and children with siblings. Further subgroup analyses, however, suggest that such average effect estimates can conceal important population heterogeneities because the only-child effect on cognitive development changes drastically between subgroups of the same population. Among other potential moderating factors, birth order and gender play particularly important roles in this process.