方法采取整群随机抽样方法选取被试，对抽取的2 015名大学生进行匿名自填问卷调查。
Methods a cluster random sample of 2 015 undergraduates were investigated with an anonymous questionnaire.
方法在北京市石景山区随机整群抽取3所学校初一到高二学生1 650人，匿名自填问卷调查。
Methods an anonymous questionnaire survey was conducted among 1 650 students drawn randomly from 3 middle schools in Shijingshan County, Beijing using a clustered sampling method.
方法：通过自填式问卷调查12个县内所有乡村医生。
Methods: All village doctors in 12 counties were surveyed with questionnaire.
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