This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'For National Immunization Programme, children surveyed in cluster sampling are \nSelect and explain. \nA. 30 cluster of 5 children, B. 20 cluster of 5 children, C. 30 cluster of 10 children, D. 30 cluster of 7 children', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Cluster Random Sampling\n\nApplicable when units of population are natural groups or clusters\nUse in India: Evaluation of immunization coverage\nWHO technique used: 30 x 7 technique (total = 210 children)\nWHO technique used in CRS: 30 x 7 technique (total 210 children)\n\t\n30 clusters, each containing\n7 children who are 12 - 23 months age and are completely immunized for\xa0primary immunization (till Measles vaccine)\nClusters are heterogeneous within themselves but homogenous with\xa0respect to each other\nSampling interval is also calculated in CR5\n\n\nAccuracy: Low error rate of only ± 5%\nLimitation: Clusters cannot be compared with each other.', 'role': 'assistant'}]