I'm running the Explore (EXAMINE) procedure in SPSS and have asked for extreme values to be listed, as well as for boxplots. The table lists five high and five low values as extremes, but the boxplot sometimes has fewer or more than this. Why is this?
Resolving The Problem
The two pieces of output are not linked and do somewhat different things. Boxplots are based on the work of John Tukey (see Technote 1479545 for details on how the elements of boxplots are defined). Outliers are defined as cases lying more than 1.5 box-lengths outside of the box, and extremes are cases lying more than 3 box-lengths distant. It is thus possible to have many or no outliers or extremes in a given data set. The table of extremes simply lists the lowest n and highest n values in the data, with a default n of 5, regardless of how far these are from the center of the data.
16 April 2020