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: Social & Preventive Medicine
[{'content': 'Berkesonian bias is a selection bias which occurs in? \nSelect and explain. \nA. Community-based studies, B. Hospital-based studies, C. Laboratory-based studies, D. Natural exposure studies', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Hospital-based studies", 'role': 'assistant'}]