The diurnal vertical migration of planktonic Ostracoda is studied based on the analysis of stratified samples of zooplanktons in the IONESS system.
根据IONESS系统对浮游动物的分层采样结果，研究浮游介形动物的昼夜垂直移动。
The survey was completed on the basis of combining stratified sampling and random sampling, collecting 1005 valid samples in total.
调查在分层逐级抽样法与随机抽样法相结合的抽样基础完成，共收集有效样本1005个。
Methods: According to the fifth national demographic investigations, the norm samples aged 10 to 15 years were collected in a stratified and random way.
方法：以年龄10～15岁少年为对象，参考第五次人口抽样调查资料，按分层随机原则取样，根据测验结果和标准化程序建立常模。
Stratified sampling method, from a polytechnic school in Qingdao test samples were 850, 809 valid questionnaires were valid for the 95.18 percent response rate.
采取分层抽样法，从青岛某理工院校抽取被试850名，收归有效问卷809份，有效问卷归收率为95.18%。
Methods: With the multistage stratified sampling, we randomly selected 400 normal children and 25 autism children as study samples.
方法采用多阶段分层随机抽样方法，选取了400例正常儿童和25例孤独症儿童为研究对象。
Stratified sampling can reduce the sampling error associated with simple random samples.
分层抽样可以减少由简单随机抽样造成的抽样误差。
Methods A sample survey based on stratified probability samples of 2 204 students aged 12~21 years old among 11 schools in four districts of Shanghai was carried out.
方法采取分层整群随机抽样的方法，对市内四个区11所学校的2 2 0 4名12～21岁的在校学生进行不记名问卷调查。
Methods A sample survey based on stratified probability samples of 2 204 students aged 12~21 years old among 11 schools in four districts of Shanghai was carried out.
方法采取分层整群随机抽样的方法，对市内四个区11所学校的2 2 0 4名12～21岁的在校学生进行不记名问卷调查。
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