Deviation bar graphs are simply two bar charts aligned, where one of the charts runs right to left rather than left to right. The two charts report on the same categories but differ in terms of respondent group or some other variable. Thus, the shared categories, such as the survey questions, are listed in the space in the middle of the two bar charts. Usually, these are constructed as bar charts, where the bars are horizontal, not column charts.
The purpose of graphing each set of responses separately from one another is so that it is easier to see the shape of each response set. Thus it is important to order one of the response sets from greatest to least, so that it is easier for a viewer to see where the other response set is out of shape.
Response sets from teachers and principals
This example shows the response sets of teachers and principals to a set of common survey questions. Principal responses are ordered greatest to least, so it becomes obvious that the teachers differed.
Source: Stephanie Evergreen
Advice for CHOOSING this option (tips and traps)
Use this option when you are looking at the overall shape of two response sets, to spot where they did not match. It is not good for comparing the responses between two groups on individual items.
Advice for USING this option (tips and traps)
Boost the ease of interpretation by colour coding the bars where the responses differ greatly between the two groups.
Making Back-to-Back Graphs in Excel: Stephanie Evergreen's blog provides step by step directions on how to make these graphs in Excel.
Other ways to compare sets of values
Illustrating the main features of the distribution of a data set in a clear way.
Presenting a frequency distribution of quantitative data in a graphical way.
Providing a way to communicate complicated data sets quickly and easily.
Using a target line to show progress to date, often with levels of performance graphed in the background.
Plotting two or more dots on a single line for each category being compared.
Positioning several small graphs with the same scale in a row for easy comparison.