Estimating the Effect of the One-Child
Policy on Sex Ratio Imbalance in China:
Identification Based on the
Difference-in-Differences
Hongbin Li
Tsinghua University
and IZA
Junjian Yi
Chinese University of Hong Kong
Junsen Zhang
Chinese University of Hong Kong
and IZA

ABSTRACT
Estimating the Effect of the One-Child Policy on
Sex Ratio Imbalance in China:
Identification Based on the Difference-in-Differences*
In China, the male-biased sex ratio has increased significantly. Because the one-child policy
only applied to the Han Chinese but not to minorities, this unique affirmative policy allows us
to identify the causal effect of the one-child policy on the increase in sex ratios by a
difference-in-differences (DD) estimator. Using the 1990 census, we find that the strict
enforcement of the one-child policy has led to 4.4 extra boys per 100 girls in the 1980s,
accounting for about 94% of the total increase in sex ratios during this period. The robust
tests indicate that the estimated policy effect is not likely confounded by other omitted policy
shocks or socioeconomic changes. Moreover, we conduct the DD estimation using both the
2000 census and the 2005 mini-census. Our estimates suggest that the one-child policy has
resulted in about 7.0 extra boys per 100 girls for the 1991-2005 birth cohort. The effect of the
one-child policy accounts for about 57% and 54% of the total increases in sex ratios for the
1990s and the 2001-2005 birth cohorts, respectively.