A stem-and-leaf plot divides each data value into a stem and a leaf
and shows the leaves corresponding to each distinct stem in the data
set in a tabular fashion. Like a histogram, the frequency of
each category (each stem in a stem-and-leaf plot) can be easily seen.
However, unlike a histogram, the individual data value can be
retrieved from the plot by combining each stem with its corresponding
leaves. For example, for the values {1.5, 2.3, 4.5, 4.8, 6.5, 8.5, 8.8, 9.5},
the stem-and-leaf plot is
Stem | Leaves |
1 | 5 |
2 | 3 |
3 | |
4 | 58 |
5 | |
6 | 5 |
7 | |
8 | 58 |
9 | 5 |
In this plot, the unit of each leaf is 0.1. The individual data value can be found by appending the stem to each of its leaf. Stems with no leaves are inserted between the first and the last stem so that all stems are evenly spaced.
The stem-and-leaf graph utility allows the user to specify a number of graph variables and an optional variable that groups the data into a number of categories. It also provides the options of specifying the leaf unit, whether the outliers should be excluded, and whether the stems with no leaves should be displayed. The leaf unit must be equal to 10x where x is an integer. Outliers are those that fall outside of the interval [first quartile - 1.5 * IQR, third quartile + 1.5 * IQR], where IQR is the interquartile range.