<prompt> Following is true about attack rate EXCEPTIt is a type of prevalence rateExpressed as percentageReflects extent of epidemicTotal population at risk is taken as denominator  <response>: An attack rate is an incidence rate usually expressed as a percent, used only when the population is exposed to risk for a limited period of time such as during an epidemic. It reflects the extent of an epidemic. Attack rate Number of new cases of a specified disease during a specified interval Total population at risk during the same interval x 100 Ref : Park 23rd edition Pgno : 131 