This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Demography and family planning, Subject name: Social & Preventive Medicine
Contraception efficacy is measured by 
Select and explain. 
A. Pearl index only, B. Pearl index and life table analysis, C. Life table analysis and couple protection rate, D. Couple protection rate and pearl index
B: Pearl index and life table analysis
Answer: B: Pearl index and life table analysis 
Explanation: Two methods that have been used to measure contraceptive efficacy are the Pearl index and life-table analysis.Pearl index is defined as the number of " failures per 100 woman-years of exposure (HWY)"Failure rate per HWY = Total accidental pregnancies / Total months of exposure x 1200The Pearl index is usually based on a specific exposure (usually one year) and, therefore fails to accurately compare methods at various durations of exposure.The life-table analysis calculates a failure rate for each month of use. A cumulative failure rate can then compare methods for any specific length of exposure.Park 23e pg: 510