There are various types of sampling which are used. They are:
This type of sampling includes the equal chances of selection of each unit in a population. There are two ways to get a random sample: with replacement and without replacement. For the former, the unit which is withdrawn and is selected from the population is returned to the population again in order to keep the population unchanged, before withdrawing, each time.
With the latter, that is, without replacement, the withdrawn unit is not retuned, and thus, the population decreases, if it is a finite population.
In this kind of sampling, the population comprises of a number of groups of cluster of units and a selected few clusters are chosen from it and examine and analysed the units present in those clusters for sampling. This is done in order to save money. Like for example, if a company manufactures some goods in cartons, they might inspect a few to ascertain the quality produced as inspecting each of those cartons and repacking them will prove to be expensive.
In stratified sampling, the population is divided into several strata and a sub sample is selected from each of these strata. The sub samples are then collected together to produce the stratified sample and is particularly beneficial when a heterogeneous population is presented with.
In this type of sampling, a unit is selected randomly from a given population, at regular intervals. This type of sampling is advantageous and preferred over simple random sampling as there are no attempts made to change the sequence of units in the given population.
Two stage sampling is done for larger groups of population. It is not feasible for such population to select a few and inspect each unit of such a group. For such instances, sampling is done in two stages. While in the first stage, some primary groups are selected randomly, in the second group however, the next sets of units are selected from the primary units.
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