<prompt> For National Immunization Programme, children surveyed in cluster sampling are30 cluster of 5 children20 cluster of 5 children30 cluster of 10 children30 cluster of 7 children  <response>: Cluster Random SamplingApplicable when units of population are natural groups or clustersUse in India: Evaluation of immunization coverageWHO technique used: 30 x 7 technique total 210 childrenWHO technique used in CRS: 30 x 7 technique total 210 children30 clusters, each containing7 children who are 12 - 23 months age and are completely immunized for primary immunization till Measles vaccineClusters are heterogeneous within themselves but homogenous with respect to each otherSampling interval is also calculated in CR5Accuracy: Low error rate of only 5Limitation: Clusters cannot be compared with each other. 