METHODS an investigation was made by cluster and stratified sampling method.
方法采用多阶段分层整群抽样方法入户调查。
Methods A cluster stratified sampling method was used to choose 3 251 students from 60 classes in 10 middle schools, among which, 3 044 questionnaires were available.
方法按照分层随机整群抽样的方法，抽取蚌埠市10所中学60个班级的3 251名高中生为研究对象，获有效问卷3 044份。
PARTICIPANTS: Totally 528 students, aged 17 to 20 years old, were recruited from grade one of year 2003 in Southwest University of Science and Technology with stratified sampling method.
对象：调查对象来源于以整群分层方法抽取的2003级在西南科技大学就读的一年级学生528名，年龄17～20岁。
Stratified sampling method was applied to investigate immunization status of ecdemic children and its affecting factors in Baoshan District.
方法采用分层抽样方法对本区外来流动儿童免疫接种现状及其影响因素进行流行病学调查。
Stratified sampling method was applied to investigate immunization status of ecdemic children and its affecting factors in Baoshan District.
方法采用分层抽样方法对本区外来流动儿童免疫接种现状及其影响因素进行流行病学调查。
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