Multistage stratified cluster sampling method was used for the sampling.
采用多阶段整群分层抽样方法。
Methods. The survey was conducted according to multi-stage stratified cluster sampling method.
方法：分阶段分层整群随机抽样调查。
Methods With stratified cluster sampling method, 2 519 students were questionnaired in Anhui province.
方法采用分层整群抽样方法，对安徽省2 519名中小学生进行问卷调查。
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