Figure 1. Example of a stem-and-leaf plot
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When creating a histogram, a scale variable is actually converted to an ordinal variable by the bins and some of the information is lost. A possible alternative is a so-called stem-and-leaf display. A ‘stem’ unit and a ‘leaf’ unit are chosen. Each number is then listed accordingly. To illustrate, let’s say we have the following ages of some customers:
17, 21, 21, 23, 28, 29, 30, 33, 35, 39, 39, 44, 45, 47, 48, 50, 50
If we choose a stem unit of 10 and a leaf unit of 1 then for the first age of 17 the stem would be 1 and the leaf 7, for 21 it will be a stem of 2 and a leaf of 1, etc. This will create the stem-and-leaf display as shown in Figure 1.
Figure 1. Example of a stem-and-leaf plot
A variation that is sometimes used is a split stem-and-leaf display. Each stem is listed twice, the first for all leafs less than 5 and the other for all leaves of 5 or more. In the example this will generate the chart shown in Figure 2.
Figure 2. Example of a split stem-and-leaf plot
Note that the leafs in the example used are ordered also because the original numbers were ordered. In the original example from Tukey (1972) the leafs are not ordered and remain in the order they appear in, nowadays the leafs usually do get ordered.
Most definitions of a stem-leaf plot often simply refer to stems and leafs.
| Stem-and-Leaf display "A method of displaying data in which each observation is split into two parts labelled the ‘stem’ and the ‘leaf’". (Everitt, 2004, p. 362) |
Note that this is also sometimes referred to as a stem-and-leaf plot, or diagram, or chart.