This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Family Planning, Subject name: Social & Preventive Medicine
Pearl index is? 
Select and explain. 
A. Failures per 1000 women-years of exposure, B. Failures per 100 women-years of exposure, C. Failures per 10 women-years of exposure, D. Failures per women-years of exposure
B: Failures per 100 women-years of exposure
Answer: B: Failures per 100 women-years of exposure 
Explanation: 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.