Tất cả các ví dụ được xem xét trong chương trước liên quan đến lấy mẫu của một số loại, cho thấy việc thiết kế các chương trình lấy mẫu là một chủ đề quan trọng trong thống kê môi trường. Vì vậy chương này là dành cho việc xem xét chủ đề này trong một số chi tiết. Ước tính giá trị trung bình, tổng số và tỷ lệ các dữ liệu thu thập được bằng cách lấy mẫu thuận tiện được bảo hiểm tại cùng một thời gian, và điều này có nghĩa là chương bao gồm tất. | CHAPTER 2 Environmental Sampling Introduction All of the examples considered in the previous chapter involved sampling of some sort showing that the design of sampling schemes is an important topic in environmental statistics. This chapter is therefore devoted to considering this topic in some detail. The estimation of mean values totals and proportions from the data collected by sampling is conveniently covered at the same time and this means that the chapter includes all that is needed for many environmental problems. The first task in designing a sampling scheme is to define the population of interest and the sample units that make up this population. Here the population is defined as a collection of items that are of interest and the sample units are these items. In this chapter it is assumed that each of the items is characterised by the measurements that it has for certain variables . weight or height or which of several categories it falls into . the colour that it possesses or the type of habitat where it is found . When this is the case statistical theory can assist in the process of drawing conclusions about the population using information from a sample of some of the items. Sometimes defining the population of interest and the sample units is straightforward because the extent of the population is obvious and a natural sample unit exists. However at other times some more or less arbitrary definitions will be required. An example of a straightforward situation is where the population is all the farms in a region of a country and the variable of interest is the amount of water used for irrigation on a farm. This contrasts with the situation where there is interest in the impact of an oil spill on the flora and fauna on beaches. In that case the extent of the area that might be affected may not be clear and it may not be obvious which length of beach to use as a sample unit. The investigator must then subjectively choose the potentially affected
