The fallacy of using NII in analyzing aircraft operations

Three measures of noise annoyance (Noise Impact Index, Level-Weighted Population, and Annoyed Population Number) are compared regarding their utility in assessing noise reduction schemes for aircraft operations. While Nil is intended to measure the average annoyance per person in a community, it is found that the method of averaging can lead to erroneous conclusions, particularly if the population does not have uniform spatial distribution. Level-Weighted Population Annoyed Population Number are shown to be better indicators of noise annoyance when rating different strategies for noise reduction in a given community.