Study design and population
The current project is a large-scale population-based cross-sectional
study conducted in northern and eastern China from 2010 to 2011. Details
about sampling, eligibility, and investigation have been introduced
elsewhere.(3) Briefly, our study utilized a multistage stratified
cluster sampling strategy to recruit participants from each stratum by
district, province/municipality,
town/township, and village/street order (Figure S1). Couples were then
approached by professional investigators with the assistance from local
officials and communities. Ultimately, 25,270 couples were approached
from 8 provinces/municipalities/cities (including Zhejiang, Anhui,
Fujian, Shandong, Beijing, Hebei, Heilongjiang, and Nei Mongol) for
their sexual and reproductive health information.Among these couples,
18,571 were interviewed, with a response rate of 74% (18,571/25,270).