This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Incidence of diarrhoea in a community can be calculated by- \nSelect and explain. \nA. Case control study, B. Coho study, C. Cross sectional study, D. Double blind placebo control study', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Coho study is also known as incidence study. The cohos are identified prior to the appearance of disease under investigation. The study group so defined are observed over a period of time to determine the frequency of disease among them. (refer pgno:75 park 23rd edition)', 'role': 'assistant'}]