For National Immunization Programme, children surveyed in cluster sampling are
Cluster Random Sampling

Applicable when units of population are natural groups or clusters
Use in India: Evaluation of immunization coverage
WHO technique used: 30 x 7 technique (total = 210 children)
WHO technique used in CRS: 30 x 7 technique (total 210 children)
	
30 clusters, each containing
7 children who are 12 - 23 months age and are completely immunized for primary immunization (till Measles vaccine)
Clusters are heterogeneous within themselves but homogenous with respect to each other
Sampling interval is also calculated in CR5


Accuracy: Low error rate of only ± 5%
Limitation: Clusters cannot be compared with each other.
30 cluster of 5 children
20 cluster of 5 children
30 cluster of 10 children
30 cluster of 7 children