This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
A population is divided into relevant subgroups and random sample selection is done from each of the subgroups. This is which type of sampling method? 
Select and explain. 
A. Systematic random sampling, B. Stratified random sampling, C. Simple random sampling, D. Cluster sampling
B: Stratified random sampling
Answer: B: Stratified random sampling 
Explanation: - in stratified random sample, the sample is deliberately drawn in a systematic way so that each poion of the sample represents a corresponding strata of the universe. - this method is paicularly useful where one is interested in analysing the data by a ceain characteristic of the population. Reference : Park's textbook of preventive and social medicine, 23rd edition, pg no:850