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Immunity, Active
Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and usually characterized by the presence of antibody produced by the host.
Immunity, Herd
The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of individual members of the group. The resistance is a product of the number susceptible and the probability that those who
Immunity, Passive
Immunity conferred by an antibody produced in another host and acquired naturally by an infant from its mother or artificially by administration of an antibodycontaining preparation (antiserum or immune globulin).
Incidence Rate
A measure of the frequency with which an event, such as a new case of illness, occurs in a population over a period of time. The denominator is the population at risk; the numerator is the number of new cases occurring during a given time period.
Incubation Period
A period of subclinical or inapparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease.
Independent Variable
An exposure, risk factor, or other characteristic being observed or measured that is hypothesized to influence an event or manifestation (the dependent variable).
Indirect Transmission
The transmission of an agent carried from a reservoir to a susceptible host by suspended air particles or by animate (vector) or inanimate (vehicle) intermediaries.
Individual Data
Data that have not been put into a frequency distribution or rank ordered.
Infectivity
The proportion of persons exposed to a causative agent who become infected by an infectious disease.
Inference, Statistical
In statistics, the development of generalizations from sample data, usually with calculated degrees of uncertainty.
Interquartile Range
The central portion of a distribution, calculated as the difference between the third quartile and the first quartile; this range includes about onehalf of the observations in the set, leaving onequarter of the observations on each side.
