2. Graphs for Categorical Variables
• Pie Charts
• Include all categories that make up a whole
• Use software to help make these
*round-off error may cause pie charts not to add up to
100%
• Bar Graphs
• Display a distribution of a categorical variable
• Compares any set of quantities that are measured in
the same units
• Leave spaces between the bars
3. Stemplots (aka stem and leaf plots)
• Let’s you see the shape of the distribution
How do you make a stemplot?
1. Separate data into stem (all values to the left of the
leaf) and leaf (only 1 digit)
2. Write all stems from smallest to largest in a vertical
column Draw a vertical line to the right of the stems
3. Write each leaf in the appropriate stem row. Make
sure they go from increasing order from the
stem outward
4. Key/labels – be sure to give a key to interpret the
stemplot as well as label it appropriately.
Example Key: 453.34 = 453.3|4
4. Back to Back Stemplots
Use a back to back stemplot to compare the
shapes of 2 distributions such as male vs. female
Put the stem in the middle of the plot
Place leaves going outward from the stem
Note: Stemplots don’t work well when you have
a lot of data with spread out stems or where
each stem must contain a large number of
leaves
5. Modifying Stemplots
• Splitting Stems
• Use a split when you have a large number of
leaves for a particular stem. 1st stem would have
leaves 0-4, 2nd stem would have leaves 5-9
Trim a stem plot by removing the last digit if
observed values have many digits that would make
the creation of the stemplot meaningless
