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
Prevalence is a: 
Select and explain. 
A. Rate, B. Ratio, C. Propoion, D. None of the above
C: Propoion
Answer: C: Propoion 
Explanation: Tools of measurement in epidemics: - Rate = x 1000/ 10000/ 100000 ; a is pa of b - Ratio = a/b ; a is not a pa of b - Propoion = x 100 = % ; a is pa of b Prevalence = No. of all current cases of a disease at a time /Estimated total population at that time X 100 Hence, Prevalence is a propoion (Prevalence is NOT a Ratio): Numerator is a pa of denominator & is always expressed in percentage. Incidence is rate.