Participants

In total, 2805 rural students from two rural middle schools (total 42 classes) in Zizhong County, Sichuan Province, China, were included in this study. In fall 2015, two middle schools were selected by using the stratified cluster sampling method from 17 rural middle schools located in hilly areas in Zizhong County. In this county, economic development and demographic characteristics, for example, the proportion of migrant workers, are similar to those of the other hilly areas in Sichuan province; thus, these schools offer a certain representativeness with respect to schools in these regions. A total of 2880 questionnaires were sent out, and 2880 were returned, for a response rate of 100%. After excluding the unqualified questionnaires, 2805 effective questionnaires were included in this study. The effective rate was 97.4%. The current cross-sectional research was the first baseline survey of a longitudinal preventive intervention program in rural western China.