Outlier

An outlier is an observation in a set of data that is inconsistent with the majority of the data. An [Page 980]observation (i.e., score) is typically labeled an outlier if it is substantially higher or lower than most of the observations. Because, among other things, the presence of one or more outliers can dramatically alter the values of both the mean and variance of a distribution, it behooves a researcher to determine, if possible, what accounts for their presence. An outlier can represent a valid score of a subject who just happens to represent an extreme case of the variable under study, it can result from failure on the part of a subject to cooperate or follow instructions, or it can be due to recording ...