<prompt> Serial interval measuresIncubation period of diseaseSensitivitySpecificityPositive predictive value  <response>: .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 