Things You Can Learn from Chinese Twins

From Hongbin Li, an economist at the Chinese University of Hong Kong, and various coauthors:

1. Why It Pays to Marry an Educated Husband
By looking at twins who married spouses with different levels of educations, Li and fellow researchers found that post-marriage income for wives rose 4.6 percent per-year of extra schooling by the husband. The relationship did not flow the other way, which the researchers say reflects male-dominance in Chinese society.

2. Is There an Income Benefit to Joining the Communist Party?
At 73 million, the number of members in the ruling Communist Party of China make up less than 7 percent of the population. This might suggest that Communist Party members are given higher paying jobs after joining, but it turns out that after investigating the incomes of identical twins (pairs where one was a member and one who wasn't), this income effect all but vanished. The authors suggest that party members are akin to ivy leaguers:

"The survival of communism in China depends on the Party, and the survival of the Party depends on the quality of its members. Our analysis shows that Party members generally have a higher ability than non-Party members, either in the form of easily observable human capital variables or in the form of unobservables. The high quality of Party members explains why they have been able to quickly come up with and effectively implement market-based reforms, and why they are able to constantly adapt to the new environment but keep the communist ideology alive (although the ideology may have weakened in the younger generation). In this sense, the fact that its members are China's elite may be an important reason for the success of the Party and of China's economic reforms."

3. More Children, Less Education
It might make intuitive sense, especially in developing countries, that there is a tradeoff between the number of children a family chooses to have and the educational attainment of those children because there is less time to devote to each of their rearings. A good way to see if this is true, proposes Li, is to find a variable that is highly correlated to the number of children in a household, but not correlated to the final educational achievement of children. And that variable happens to be, you guessed it, twins. Li found that there was indeed a tradeoff between quantity and education, but that it only existed for rural China, not urban.