This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Following is true about attack rate EXCEPT 
Select and explain. 
A. It is a type of prevalence rate, B. Expressed as percentage, C. Reflects extent of epidemic, D. Total population at risk is taken as denominator
A: It is a type of prevalence rate
Answer: A: It is a type of prevalence rate 
Explanation: An attack rate is an incidence rate (usually expressed as a percent), used only when the population is exposed to risk for a limited period of time such as during an epidemic. It reflects the extent of an epidemic. Attack rate = Number of new cases of a specified disease during a specified interval / Total population at risk during the same interval x 100 Ref : Park 23rd edition Pgno : 131