<prompt> Failure rate of contraceptive method is determined byPearl indexHalf lifeNumber of accidental pregnanciesPeriod of contraceptive practice continued  <response>: Two methods have been used to measure contraceptive efficacy: 1. Pearl index and 2. Life table analysis Pearl index is defined as the number of failure rates per 100 woman years of exposure Reference : Park;s textbook of preventive and social medicine, 23rd edition, Page no: 510 