This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraceptives, Subject name: Gynaecology & Obstetrics
[{'content': 'Which of these is used to measure contraceptive efficacy? \nSelect and explain. \nA. Pearl index, B. William rate, C. Quasi-rate, D. AFS score', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The use-effectiveness of contraceptive method is expressed by Pearl rate . Pearl rate or pearl index was introduced by Raymond Pearl in 1932. It is calculated as: total accidental pregnancies x 1200 / number of women observed x total months of contraceptive use It is expessed as HWY (hundred women years) AFS ( American feility Society ) score predicts severity of endometriosis and risk of recurrence after surgery', 'role': 'assistant'}]