Sampling a Site or Region with Spatial Units
Sometimes the sampling elements available for selection are not the same as the elements we wish to study. This happens most frequently in archaeology in spatially based sampling, as in the excavation of a sample of grid squares in a site or the survey of a sample of grid squares or transects in a region. For instance, suppose we have a random sample of 500 sherds from a site. We may want to estimate, say, the mean thickness of sherds at the site or the percentage of a particular pottery type in the sherds at the site. The elements studied are sherds. Suppose the sample had been obtained by excavating a random sample of 10 grid squares. The sampling element here is not the sherd but the grid square. It was 10 grid squares that were randomly selected from all the squares in the site grid, not 500 sherds from all the sherds in the site. We thus have a sample, not of 500 independently selected elements, but of 10 independently selected elements, and these elements do not correspond to the elements we need to study. Each sampling element is, in this case, a group or cluster of a varying number of the elements of study (sherds). This fact must be allowed for in making estimates of means or proportions.
KeywordsCluster Sampling Error Range Simple Random Sampling Spatial Unit Sampling Element
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