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
[{'content': 'Serial interval measures \nSelect and explain. \nA. Incubation period of disease, B. Sensitivity, C. Specificity, D. Positive predictive value', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .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', 'role': 'assistant'}]