Variation is how 'spread out' the data are. It can also be called dispersion or scatteredness.
Variation is seen in raw data as they are collected, in summary tables and of course in many kinds of graphical representations. Research has shown that variation is the first characteristic of data that young students recognise.
The stacked dot plot below, generated using TinkerPlots software, shows variation in the arm spans of 60 students.
