eFigure1. Flowchart on sampling process Forth stage ...

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Forth stage. 5,400 households. 100 houses per village were systematically selected. First stage. 9 counties. Stratified by three ... Fifth stage. 2 members in each.
First stage

Stratified by three GDP levels, for a total of 101 counties in Inner Mongolia; three counties were randomly selected from each GDP stratum.

9 counties

Second stage

2 towns per county were systematically selected.

18 towns

Third stage

3 villages/communities per town were systematically selected.

54 villages/communities

Forth stage

100 houses per village were systematically selected.

5,400 households

Fifth stage

2 members in each household were selected, whose birthdays were closest to the survey date.

10,800 subjects

10,581 for analysis (Excluded 196 inaccessible subjects, and 23 subjects with systematic errors in questionnaires) eFigure1. Flowchart on sampling process