How Do Outliers Affect Mean, Median, Mode and Range in a Set of Data?

Dave Dugdale/CC-BY-SA 2.0

A mathematical outlier, which is a value vastly different from the majority of data, causes a skewed or misleading distribution in certain measures of central tendency within a data set, namely the mean and range, according to About Statistics. The affected mean or range incorrectly displays a bias toward the outlier value. The median and mode values, which express other measures of central tendency, are largely unaffected by an outlier.