Introduced in 1801 by Scottish engineer, William Playfair, pie charts are a very common, but controversial way to visualize data. While pie charts are often depicted as simple and easy to create statistical tools the pie chart has become a divisive tool that many individuals, especially those in business, hate for the way pie charts potentially mislead visual representations of concepts. At HelloInfo, pie charts are used in selective situations when visualizing data. Let’s take a deeper look into these controversial charts to identify best practices to avoid common pie chart mistakes.
The origins of pie charts
Since their inception, pie charts were praised for their readability, and William Playfair argued that the charts communicated information better than a table of data. One of Playfair’s first pie charts depicted the area of the Turkish Empire before 1789. His version was the first pie chart to display empirical proportions and to differentiate the component parts by colour.
Despite Playfair’s efforts, it was not until French engineer Charles Joseph Minard used pie charts to depict the number and proportions of butcher meat supplied to various areas of Paris, and English nurse/statistician Florence Nightingale used them to depict the number of unnecessary deaths in British hospitals during the Crimean war, that the charts became more popular.
Over time, opponents of pie charts emerged. One of the most prevalent arguments against the use of pie charts is that they are not a good way to represent data. Experts believe that it is easier for those consuming data visualizations to compare lengths, such as in a bar chart or line graph, than it is to compare angles in a pie chart. Pie charts appeal to most because of their simplicity, not their effectiveness.
Pros and cons
Pie charts are excellent at visualizing a “parts to a whole” relationship. The shape is familiar and taking a “slice” out of a whole is a simple way of representing a fraction or percentage of data. An example of this can be found in visualizations of customer satisfaction surveys. In these surveys its common to have questions such as “do you like this product offering?” with response options of “yes,” “no,” and “unsure.” When visualized in a pie chart, these answers reflect the percentages of each answer in relation to the whole demographic surveyed (100%). Additionally, pie charts provide a straightforward and easy-to-understand illustration that does not require observers to analyze additional features such as the scale of an axis.
A major disadvantage of pie charts is that they lose their effectiveness when too many data points or variables are included. Using the same example as above, if the response options to the question “do you like this product offering?” were not only “yes,” “no,” and “unsure,” but allowed respondents to submit varied individual responses, each potential response could be different creating a very crowded pie chart. While pie charts present an easy approach to viewing data, they can skew the information being presented when multiple variables are represented with similar values. An example of this issue can be seen below.
Both pie charts look similar, however, when the same data is represented in a bar chart you can see that there are differences between them that are not apparent when you are looking at the pie chart alone.
Best practices for pie charts
With the divide between pie chart fans and critics in mind, let’s look at some best practices that HelloInfo uses to ensure that the pie charts we use are accurately representing our clients’ data.
- Being very selective: Ensuring pie charts are only used in situations where they make the most sense, typically when a simple concept is being portrayed.
- Information types: Pie charts are great for showing fractions of a whole; not all data collected falls into this information type. This distinction is important as selecting the right chart, whether it be a pie chart or line chart, will affect the level of impact the data you are presenting has.
- Including data labels: By including data labels some of the nuances that may be lost in the graphical representation of the data are highlighted.
- Use of different types of pie charts: There are many variations of pie charts that exist, such as donut charts, irregular pie charts, 3D pie charts and ‘exploded’ pie charts. Each pie chart variation offers a different visual effect that can elevate the visual being portrayed.
- Simplicity is key: Pie charts are best kept to a maximum of 5, and even then we often will not use more than 2 or 3 categories. When more than 5 categories are included, the pie chart can become crowded and difficult to read, detracting from the key takeaway of the data.
At HelloInfo we use many different chart types to visualize data, including pie charts selectively. Sometimes it is necessary to create multiple data visualization options to determine which version will be most impactful for our clients’ needs. If you are interested in learning more about how HelloInfo can help with your data visualization needs, please schedule a call with us.