Methods With the equal proportion sampling, 5,489 elementary and middle school students were selected to test the visual acuity and a questionnaire survey was conducted among them.
方法采用等比抽样法对宝鸡市5 489名中小学学生进行了视力测试和问卷调查。
Methods With the equal proportion sampling, 5,489 elementary and middle school students were selected to test the visual acuity and a questionnaire survey was conducted among them.
方法采用等比抽样法对宝鸡市5 489名中小学学生进行了视力测试和问卷调查。
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