Pearl index is?

ANSWER: (B) Failures per 100 women-years of exposure REF: Park 20th edition page 439 EVALUATION OF CONTRACEPTIVE METHODS:Two methods that have been used to measure contraceptive efficacy are Pearl index and life table analysis.I. Pearl index:Pearl index is defined as number of failures per 100 women-years of exposure (HWY). Pearl index is usually based on a specific exposure (usually 1 year) and therefore fails to accurately compare methods at various durations of exposure. This limitation is overcome by using the method of life table analysis.This rate is given by formula:Failure rate per HWY =Total accidental pregnancies Total months of exposurex 1200II. Life-table analysis:This calculates the failure rate for each month of use. A cumulative failure rate can then compare methods for any specific length of exposure.