Fig. 1.

Study profile. NHSS=National Health Service Surveys in China. ^aA multistage stratified cluster sampling method was used in these surveys. The mainland China was first divided into east, central and west regions. We sampled 156 counties each year stratified by region and residence. ^bUnreasonable data with z scores of height for age <−6.0 or >6.0 (age<19), weight for age <−6.0 or >6.0(age<10), and BMI for age <−6.0 or >6.0(age<19) were excluded from the final analysis. Missing values for height, weight, gender, or age were also excluded in the final analysis.