This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Case Control Study, Combined Designs, Subject name: Social & Preventive Medicine
[{'content': 'A study is looking at breast cancer of women compared cases with non-cases, and found that 75/100 cases used calcium supplements compared with 25/100 of the non-cases. Calculate Cross product ratio \nSelect and explain. \nA. 9, B. 6, C. 3, D. 12', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Odds ratio = ad/bc Breast cancer cases Non-cases Used Ca supplements 75 (a) 25 (b) Did not use Ca supplements 25 (c) 75 (d) 100 100 Odds ratio = ad/bc = 75*75/25*25 = 9', 'role': 'assistant'}]