<prompt> Which of the following is TRUE regarding pearl index?Failures per 1000 women-years of exposureFailures per 100 women-years of exposureFailures per 10 women-years of exposureFailures per women-years of exposure  <response>: The pearl index is defined as number of failure per 100 woman years of exposure. The denominator is the total months or cycles of exposure from the onset of method until completion of study. The Pearl Index is sometimes used as a statistical estimation of the number of unintended pregnancies in 100 woman-years of exposure. 