An Investigation of the Effect of the Swamping Phenomenon on Several Block Procedures for Multiple Outliers in Univariate Samples

In its broadest sense, this paper reviews the general outlier problem, the means available for addressing the discordancy (or lack thereof) of an outlier (or outliers), and possible strategies for dealing with them. Two alternate approaches to the multiple outlier problem, consecutive and block testing, and their respective inherent weaknesses, masking and swamping, are discussed. In addition, the relative susceptibility of several tests for outliers in normal samples to the swamping phenomena is reported.