Multivariate Outliers and the O3 Plot

Abstract

Identifying and dealing with outliers is an important part of data analysis. A new visualization, the O3 plot, is introduced to aid in the display and understanding of patterns of multivariate outliers. It uses the results of identifying outliers for every possible combination of dataset variables to provide insight into why particular cases are outliers. The O3 plot can be used to compare the results from up to six different outlier identification methods. There is an $R$ package OutliersO3 implementing the plot. The article is illustrated with outlier analyses of German demographic and economic data. Supplementary materials for this article are available online.

Keywords:

• Data science
• Data visualization
• Exploratory data analysis
• OutliersO3
• Parallel coordinate plots
• Statistical graphics