Special Incidence Rates:
(a) Attack rate: The attack rate is defined as number of new cases of a specified disease during a specified time interval per 100 populations at risk during the same time interval. An attack rate is used only when the population is exposed to risk for a limited period of time such as during an epidemic.
Formula:
Number of new cases of a specified disease
during a specified time interval
Attack rate = ------------------------------------------------------------ X100
Total population at risk during the same time interval
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