Fig. 1.

Study areas and targeted sampling sizes of the JECS as of January, 2011.

Fifteen regional centers were selected in a competitive process in which universities and other research institutions were invited to submit proposals for the covered areas, population, recruitment methods, organization structures, regional liaison, and resources. The JECS aims to cover half of all the births in the area. Selected regional centers were required to recruit 3,000 to 9,000 pregnant women over a period of 3 years, totaling 100,000 participants in 15 regional centers. This figure is cited in “Reference 1” and is partially modified.