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': 'A research is conducted to assess the nutritional status of the children in a particular district. For this purpose, 2 children are randomly selected from every school in the district. This type of sampling is known as: \nSelect and explain. \nA. Simple random, B. Systematic random, C. Stratified random, D. Cluster', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Cluster sampling\xa0\nThis method is used when the population forms natural groups or clusters, such as, villages, wards blocks or children of a school etc. First a sample of the clusters is selected and then all the units in each of the selected clusters are surveyed. This method is simpler and involves less time and cost, but gives a high standard error.\xa0\nStratified Random Sampling\xa0\nA stratified random sample is obtained using the following procedure:\xa0\ni) The\xa0 population\xa0 to\xa0 be\xa0 sampled\xa0 is subdivided into groups known as strata, such that each group is homogeneous in\xa0its characteristic.\xa0\nii) A simple random sample is then chosen from each stratum. This type of sampling is\xa0 used\xa0 when\xa0 the\xa0 population\xa0 is\xa0heterogeneous\xa0 with\xa0 regard\xa0 to\xa0 the characteristic understudy. For example, to determine the prevalence of DMF teeth in different age groups, the different age groups form the strata and a random sample is to be chosen.', 'role': 'assistant'}]