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
The failure rate per HWY of Pearl index is given by 
Select and explain. 
A. x 1200, B. x 2400, C. x 1200, D. x 2400
C: x 1200
Answer: C: x 1200 
Explanation: The Pearl index is defined as the number of failures per 100 women-years of exposure . This rate is given by the formula:Failure rate per HWY: x 1200The factor 1200 is the number of months in 100yearsRef: PArk; 23rd ed; Pg 510