Chinese Child Twins Survey （CCTS）

下面是一些简单介绍：

The survey was carried out by the Urban Survey Unit (USU) of the National Bureau of Statistics (NBS) in late 2002 and early 2003 in the Kunming district of China. Kunming is the capital of Yunnan Province, which is located in the far southwestern corner of China and has a total population of about 5 million. The CCTS includes a sample of households with twins aged between 6 and 18 years living in Kunming in 2002. The households were initially identified by the USU based on the 2000 population census according to whether the children have the same birth year and month and the same relationship with the household head. The addresses of these households were then obtained from the census once, and the presence of twins was varied with a visit to the household.
Starting from 2,300 pairs of potential twins identified in the census, 1,694 households with twins were successfully interviewed; among these, 1,300 households had twins on the est birth and 394
households had twins on the second birth.36 A comparison sample of 1,693 households with no twins was also surveyed using the same questionnaire.

cited from "Early Health Shocks, Parental Responses, and Child Outcomes" Gabriella Conti, James J. Heckman, Junjian Yi, Junsen Zhang