<prompt> All are true about cluster sampling except ?Sample size is same as that of simple random samplingIt is a two stage samplingIt is cheapter than other methods of samplingIt has a disadvantage of higher sampling error  <response>: Ans. is a i.e., Sample size is same as that of simple random sampling o Cluster sampling is an example of two-stage sampling or mulistage sampling - i In first stage a sample or areas is chosen In the second stage a sample of respondent within those areas is selected. o Cluster sampling generally increases the variability of sample estimates above that of simple random sampling, depending on how the clusters differ between themselves, as compared with the within-cluster variation. It has a disadvantage of higher sampling error, which is difficult to measure. Impoant facts of cluster random sampling CRS o Cluster sampling is used in India to evaluate immunization coverage. o WHO used 30 x 7 technique total 210 children for cluster sampling in which there are 30 clusters, each containing 7 children who are 12 - 23 months old and are completely immunized for primary immunization till measles vaccine at 9 month o Clusters are heterogenous within themselves but homogeneous with respect to each other. o Main objective of cluster sampling is to reduce costs by increasing sampling efficiency; in contrast to stratified sampling where; the main objective is to increase precision. o Cluster sampling is quiet accurate with low error rate of only - 5. o Cluster sampling can also calculate sampling interval. o The main limitation of cluster sampling is that cluster cannot be compared with each other. 