<prompt> Best index for measuring contraceptive efficacy isPearl indexLife-table analysisChandlers indexQuetlet index  <response>: Life table analysis : Calculates a failure rate for each month of use Cumulative failure rate can then compare methods of any specific length of exposure Women who leave a study for any reason other than unintended pregnancy are removed from analysis, contributing their exposure until the time of exit Reference : Park;s textbook of preventive and social medicine, 23rd edition, Page no: 510 