WHO immunization evaluation coverage survey is normally done in what age group?

Ans. is 'c' i.e., 12-23 months WHO used 30 x 7 technique (total = 210 children) for cluster sampling in which there are 30 clusters, each containing 7 childrenwho are 12 - 23 months old and are completely immunized for primary immunization (till measles vaccine at 9 month).