Stem and Leaf Plot 6R

A stem and leaf plot looks something like a bar graph. Each number in the data is broken down into a stem and a leaf, thus the name. The stem of the number includes all but the last digit. The leaf of the number will always be a single digit.

Elements of a good stem and leaf plot
-shows the first digits of the number (thousands, hundreds or tens) as the stem and shows the last digit (ones) as the leaf.
-usually uses whole numbers. Anything that has a decimal point is rounded to the nearest whole number. For example, test results, speeds, heights, weights, etc.
-looks like a bar graph when it is turned on its side.
-shows how the data are spread—that is, highest number, lowest number, most common number and outliers (a number that lies outside the main group of numbers).

Tips on how to draw a stem and leaf plot
Once you have decided that a stem and leaf plot is the best way to show your data, draw it as follows:
-On the left hand side of the page, write down the thousands, hundreds or tens (all digits but the last one). These will be your stems.
-Draw a line to the right of these stems.
-On the other side of the line, write down the ones (the last digit of a number). These will be your leaves.
For example, if the observed value is 25, then the stem is 2 and the leaf is the 5. If the observed value is 369, then the stem is 36 and the leaf is 9. Where observations are accurate to one or more decimal places, such as 23.7, the stem is 23 and the leaf is 7. If the range of values is too great, the number 23.7 can be rounded up to 24 to limit the number of stems.

Example 1 – Making a stem and leaf plot
Each morning, a teacher quizzed his class with 20 geography questions. The class marked them together and everyone kept a record of their personal scores. As the year passed, each student tried to improve his or her quiz marks. Every day, Elliot recorded his quiz marks on a stem and leaf plot. This is what his marks looked like plotted out:
Table 1. Elliot's scores on the basic facts quiz last year Stem Leaf

 0 3 6 5 1 0 1 3 4 5 5 6 6 7 8 9 9 2 0 0 0 0

Double Stem and Leaf Plots
Double stem and leaf plots are used to compare two distributions side-by-side. This type of double stem and leaf plot contains three columns, each separated by a vertical line. The center column contains the stems. The first and third columns each contain the leaves of a different distribution. The numbers for the leaves of the distribution in the leftmost column are aligned to the right and are listed in order.
Stem-and-leaf plots are not restricted to 2-digit numbers. As well, a double stem and leaf plot is possible.

Example 2 - Making a double stem and leaf plot
The data:
Cars: 123, 125, 129, 131, 127, 99, 136
Vans: 89, 93, 101, 112, 109, 145, 104, 108, 109

A stem-and-leaf plot of this data is:

*Note: the left side data may also be listed in order with the smallest against the stem and increasing as it goes left, right side always goes from smallest to largest going left to right.

Legend: A stem and leaf plot and a double stem and leaf plot should include a legend to give the value of the stem and leaves.

| 5 | 3  = 53        7 | 8 | = 87          |1.2 | 2 = 1.22

Example 3 - Making a double stem and leaf plot
The following is an example of a double stem-and-leaf plot showing the test scores for two classrooms on a common test. The test scores were put in order and entered into the graph. All scores are entered. Mrs.Day's class had scores from 54 to 100 and Mr. Knight's class had scores from 59 to 100.