Area Sampling

Area Sampling:

Area sampling is a form of multi-stage sampling in which maps, rather than lists or registers, are used as the sampling frame. This method is more frequently used in those countries that do not have a satisfactory sampling frame such as population lists

In area sampling, the overall area to be covered in a survey is divided into several smaller areas within which a random sample is selected Thus, for example, a city map can be used for area sampling Various blocks can be identified on the map and this can provide a suitable frame The entire city area can be divided into these blocks which are then numbered and from which a random sample is finally drawn

In sampling the blocks, stratification and sampling with probability proportional to a measure of size are commonly employed. However, stratification in area sampling is based on geographical considerations Thus, when blocks are identified and numbered on the map, they can be grouped into some meaningful strata representing the different neighborhoods of the town. The point to emphasize is that these blocks must be identifiable without any difficulty

On the basis of the blocks thus identified, numbered and assigned to strata, a stratified sample of dwellings can be selected This can be done in either of two ways First, a sample of dwellings may be drawn from all the dwellings included in a selected block Second, blocks may be divided into segments of a more or less equal size, and a sample of these segments can be chosen and finally all the dwellings from the selected segments may be taken in the sample It will thus be seen that the second method introduces another stage of sampling, namely, segments

Although the above discussion relates to area sampling with respect to a city or town, the same approach is applicable to a large area, say, a state or a country, the only difference being that one or more additional stages of sampling may have to be introduced

Finally, it may be pointed out that area sampling is perhaps the only possibility if a suitable sampling frame is not available