<prompt> Which of these is used to measure contraceptive efficacy?Pearl indexWilliam rateQuasi-rateAFS score  <response>: 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 