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 Questionnaire and multistage stratified cluster sampling method were used for the survey.
方法进行问卷调查；采用多阶段整群分层抽样方法。
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