4.8 A Stem-and-Leaf plot
Data can be shown in a variety of ways including graphs, charts and tables. A stem-and-leaf plot is similar to a histogram but displays more information. The stem-and-leaf plot indicates the shape of a set of data (the distribution) and provides extra detail regarding individual values. The data are arranged by place value. The digit in the largest place is referred to as the stem and the digits in the smallest place are referred to as the leaf (leaves). The leaves are always displayed to the left of the stem. Stem and leaf plots can be used to organise large amounts of information.
They are usually applied if large amount of numbers are to be analyzed. Series of score of sports teams, series of temperatures or rainfall over a period of time and series of classroom test scores are examples of data for which stem-and-leaf plots can be used for analysis.
Let us consider some examples.
The subjects in a psychological study were timed while completing a certain task.
Complete a stem-and-leaf plot for the following list of times:
First we should rearrange this list in order of magnitude as:
These values have one decimal place, but the stem-and-leaf plot makes no accomodation for this. The stem-and-leaf plot only looks at the last digit (for the leaves) and all the digits before (for the stem). So, we will have to pit a "key" or legend. The ones digits will be the stem values and the tens will be the leaves.
Task completion times