This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Definitions & Concepts, Subject name: Social & Preventive Medicine
Failure rate of contraceptive method is determined by: 
Select and explain. 
A. Half life index, B. Pearl index, C. Total feility rate, D. Age specific feility rate
B: Pearl index
Answer: B: Pearl index 
Explanation: - Pearl's Index: Measures the failure rate/ efficiency of a contraception. PI = Total No. of accidental gestations/ Total months of exposure x 1200 It is expressed per Hundred women years .