要进行一次系统随机抽样，必需知道人群中的家庭总数，平均每户家庭5岁以下儿童的个数，以及总人口。
To undertake a systematic random sampling, one needs to know the total number of households, the average number of children under 5 years of age in a household, and the total population.
该计划在美国第一次采用随机抽样的方法进行鱼体组织调查，并得到了有史以来最详尽的鱼体毒物残留数据。
It is the first national fish tissue survey to be based on a probabilistic (random) sampling design, and it will generate data on the largest set of PBT chemicals ever studied in fish.
该计划在美国第一次采用随机抽样的方法进行鱼体组织调查，并得到了有史以来最详尽的鱼体毒物残留数据。
It is the first national fish tissue survey to be based on a probabilistic (random) sampling design, and it will generate data on the largest set of PBT chemicals ever studied in fish.
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