A stem and leaf plot is a tool for examining the distribution of a single numeric variable. For example, you could make a stem and leaf plot of the heights of students in a class. Stem and leaf plots are most useful when the number of subjects is not more than about 100. The stem is the first part of the value, and each particular value is written as a leaf. For example, in the height example, the stems might be height in feet, ranging from perhaps 4 to 6, and each leaf would be the weight of one student. Usually, each stem is one line, but using two lines per stem is useful when the stems each have a lot of leaves.
Sort the data from smallest to largest.
Decide on a stem. The stem will be the first part of the values. For example, if you have data on the heights of students in feet and inches, the stem would be number of feet, and there would (almost certainly) be two stems 5 and 6, and possibly a 4 (if you had subjects who were less than 5 feet tall).
Write each leaf. Use multiple lines if the plot starts to become hard to read. There are no firm guidelines on this, it is a matter of judgment. For example, if you had data on 40 students, the stem and leaf plot might look like this: 6 0 0 1 1 2 3 4 5 6 6 7 7 7 8 8 8 9 9 10 10 11 11 5 0 0 1 1 1 2 2 3 3 4 4 4 5 5 5 5 5 4 11 11 Note that there can be two lines for some stems and one line for others.
About the Author
Peter Flom is a statistician and a learning-disabled adult. He has been writing for many years and has been published in many academic journals in fields such as psychology, drug addiction, epidemiology and others. He holds a Ph.D. in psychometrics from Fordham University.
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