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 measures 
Select and explain. 
A. Incubation period of disease, B. Sensitivity, C. Specificity, D. Positive predictive value
A: Incubation period of disease
Answer: A: Incubation period of disease 
Explanation: .serial inetrval is the time gap between the onset of primary cases and the secondary cases.by collecting information on the whole series if such onsets,we get a distribution of secondary cases from which we can guess the incubation period of disease. ref:park&;s textbook ,22 nd edition,pg no 96