<prompt> Contraceptive efficacy expressed as100 women months1000 women years100 women years10 women years  <response>: Contraceptive efficacy is assessed by measuring the number of unplanned pregnancies that occur during a specified period of exposure and use of contraceptive methods.Contraceptive efficacy is measured using Pearl index and life table analysis. Pearl index is number of failure per 100 woman-years of exposure HWY HWYtotal accidental pregnanciestotal months of exposure.1200 Life table analysis measure failure rate per month of exposure. Park;s textbook of preventive and social medicine.K Park. Edition 23.Pg no: 510 