All calculations were weighted to represent the total Chinese adult
population 35 to 74 years of age. The weights were calculated on the
basis of the 2000 China Population Census data and InterASIA
sampling scheme and took into account several features of the
survey, including oversampling for specific age or geographic
subgroups, nonresponse, and other demographic or geographic
differences between the sample and the total population. Standard
errors were calculated by a technique appropriate to the complex
Figure 1. Map of China with study sites
(north China: Jilin, Beijing, Qinghai,
Shanxi, and Shandong; south China:
Sichuan, Hubei, Shanghai, Fujian, and
Guangxi).
406 Circulation July 27, 2004
survey design. All data analyses were conducted by use of STATA
7.0 (Statistics/Data Analysis) software.