Methods A total of 7482 residents aged 15-69 selected in representative 30 counties through multi-stage random sampling from Zhejiang Province were surveyed by using questionnaire.
方法采用多阶段随机抽样的方法，在浙江省有代表性的30个县区，对7482名年龄在15～69岁的居民进行面对面问卷调查。
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。
Large-scale sample surveys are always undertaken with stratified multi-stage sampling.
大型抽样调查总是采用分层多阶段抽样。
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