This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which one of the following is true regarding case fatality rate? 
Select and explain. 
A. Numerator is always constant, B. Denominator is always constant, C. Numerator and denominator are propoions of each other, D. Numerator and denominator are two separate entities
D: Numerator and denominator are two separate entities
Answer: D: Numerator and denominator are two separate entities 
Explanation: Case fatality rate = No. of deaths due to disease / No. of infected people Case fatality rate (CFR) is the ratio of deaths within a designated population of "cases" (people with a medical condition), over the course of the disease. A CFR is conventionally expressed as a percentage. CFRs are most often used for diseases with discrete, limited time courses, such as outbreaks of acute infections.