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': 'In case control study, the risk is calculated by- \nSelect and explain. \nA. Relative risk, B. Attributable risk, C. Cross product ratio, D. None', 'role': 'user'}, {'content': "Answer: C \nExplanation: Also known as odds ratio Measure of strength of relations between risk factor and outcome. The disease being investigated is very rare The cases must be representative of those with disease The controls must be representative of those without disease Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 81", 'role': 'assistant'}]