Cluster Sampling

In cluster sampling there  is  a successive random . sampling of units. The first unit  to  be sampled is large grouping or clusters. For example,  in  drawing a sample of nursing students, researcher might first draw a random sample of nursing schools of  the  country. To draw the schools of nursing, the random selection of  the State have  to  be done. So the usual  procedure for selecting general sample of  students is first to select states, cities, districts, then  schools and  students successively. Although cluster sampling may be necessary for large scale survey studies, the chance of sampling errors  increases with  each  stage of  sampling. Despite the disadvantage cluster sampling  is considered more economical and practical  than other  types of probability sampling, particularly when population  is  large and widely disperse.