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
What is the denominator in calculation of incidence - 
Select and explain. 
A. Number of fresh cases, B. Number of symptomatic cases, C. Total number of cases, D. Population at risk
D: Population at risk
Answer: D: Population at risk 
Explanation: Incidence is defined as new cases occurring in a defined population during a specified period of time. Incidence =(number of new cases of specific disease in a given time proof\population at risk during that period) 100 (refer pgno:60 park 23 rd edition)