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
Serial interval is a measure of 
Select and explain. 
A. Sensitivity, B. Specificity, C. Incubation period, D. Positive predictive value
C: Incubation period
Answer: C: Incubation period 
Explanation: The gap in time between the onset of primary case and the secondary case is known as serial interval. By collecting information of the whole series of onset, we get a distribution of secondary cases from which we can guess the incubation period. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 108