In my last four articles I’ve been addressing how best to report the results from your surveys. My emphasis has been on the use of graphical displays. Before I leave this subject I want to provide some general tips for displaying your data. The goal is graphical excellence, which we define as communicating ideas as clearly, precisely and efficiently as possible while letting the data reveal the truth.
The interested reader might want to refer to Edward R. Tufte’s 2001 book, The Visual Display of Quantitative Information for a more detailed account on how to make sure your reports have “graphical integrity.” It is an excellent book.
Tips for Maintaining Graphical Integrity
1. Always include the number, N, of observations on your chart.
This simple addition to any chart (see example below*) is critical to understanding the data presented. Including the number of observations on your chart let’s the reader reconstruct your data from the percentages given. It also provides an indirect measure of the variability one might expect to see.
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2. Use counts instead of percents when N is small, fewer than 10 to 15.
When you have a very small number of survey respondents it is better to plot counts than the percentage of counts (see following two charts). Even though it is possible for the reader to calculate the counts on his or her own, going to counts for small numbers helps the readability of a chart by eliminating the extra step. The human brain can read and interpret small numbers quickly and without ambiguity.
Image may be NSFW.
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Image may be NSFW.
Clik here to view.
3. Don’t overload your chart or graph.
It is important that your reader be able to get information quickly and efficiently from your chart of graph. There is often a tendency to add too many items to your graph that do not add to the data’s message. Often “non-data” items (e.g. 3-D images) are included that can detract from or mask the true information. Even if you include only data on the chart, it is easy to overload it will information.
The following example shows a common mistake, which leads to a chart that is difficult interpret.
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The most critical piece of the data from the chart above is the trend information. Therefore it is best to emphasize that element of the data. If, in addition, you combine the percentages for “Much better” and “Better” as well as for “Worse” and “Much worse,” the chart becomes much easier to read and interpret (see below).
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4. Show all of your data.
The complete truth about a data set usually extends beyond what you can fit on a single chart or graph, but you need to strive to show all available data. For example, suppose a manufacturer comes out with a new product release and wants to see what effect the new release has had on service calls. The chart below shows the number of product service calls for the year before the release compared to the same number after the new release.
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This seems like a reasonable approach but the two years of data do not begin to tell the whole story. Showing all of your available data better represents the true situation (see chart below). The two charts give substantially different pictures.
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As I’ve talked about many times, graphical displays of data can be powerful communication tools. If you follow these few tips it should help you provide clear and concise information and avoid charts that are confusing or misleading to your readers. In my next article I’m going to return to the topic of writing surveys, by going over the top ten most common mistakes made when writing surveys.
*NOTE: The charts and graphs in this blog post were generated by exporting a CSV of SurveyGizmo survey data into Excel.