How to Create Double Bar Graphs

Double bar graphs allow the viewer to make quick generalizations about differences within and between data groups.

Bar graphs are best suited to displaying data with a qualitative, rather than quantitative, independent variable. With qualitative variables there is no uniform distance between levels making the discrete nature of individual bars well suited for this type of chart. Double bar graphs are used when the data uses two independent variables and thus two different sets of frequency data. Double bar graphs, or grouped bar graphs as they are called when more than two independent variables are present, allow the viewer to make quick generalizations about differences within and between data groups.

Things You'll Need

• Data
• Pencil
• Paper

Instructions

Directions

1. Draw the axes of your graph. Draw a horizontal line to represent the independent variable. Draw a vertical line on the far left side of the horizontal line to represent the dependent variable.

2. Label the vertical axis with the units used to measure the dependent variable. The dependent variable is what is being measured in the experiment and displayed on the chart. The dependent variable changes based on the independent variable. Number of students, height, and weight are all examples of possible dependent variables.

3. Label the horizontal axis with the qualitative categories used to distinguish the independent variable. These can be things like hair color, eye color, or home state. Be sure to leave enough room for two bars to be drawn for each category.

4. Take the data from each qualitative category and split it in two with regards to the second independent variable being used. For example, if you are making a graph concerning the hair color of students in your classroom based on their sex; then the number of students would be the dependent variable, hair color would be the first independent variable used in step four, and you would divide the number of students with each hair color up depending on the second independent variable their sex.

5. Draw two bars representing the value of the dependent variables found for each pair of data-sets after the division of data in step four. Draw the pairs of bars touching each other but not touching the bars in other categories.

6. Title the graph and label each axis with the variable it represents and the unit used to measure the variable.

References

• NC State University LabWrite Resources: Bar Graphs
• Syracuse University Special Topics in Bar Graphs: Double Bar Graphs
• NC State University LabWrite Resources: Graphing With Excel
• Syracuse University: Constructing Bar Graphs
• NC State University LabWrite Resources: Dependent Variable