A pie chart? Maybe not
Nowadays, we live in the era of Big Data, Machine Learning, and several other buzzwords that are fascinating for everyone. However, there is another one that already existed in the past and which these technologies allowed to grow in terms of relevance: Data Analytics! Regardless of being a Data Scientist, who builds your reports using a programming language, or knowing only how to use a spreadsheet program, this article is for you!
By now, you should be asking yourself: “What is it that links a Data Scientist to somebody using any spreadsheet program?” and the answer is that you have to represent Data. Thus, this is valid for a high school student, a university student, a Data Scientist, a consultant or any other person responsible to represent Data for somebody else.
One of the most popular ways to represent Data is by using pie charts and today I will be showing you 4 situations in which such a chart is not advisable.
- Do not use a pie chart to represent absolute quantities
One common mistake that is made by many people is the fact that they represent absolute quantities, while they should be used to represent relative quantities. This stems from the fact that this chart represents, by default, a whole composed of several parts. Additionally, if you look at the example above, you can notice immediately which slice is the biggest and which slice is the smallest, but the absolute values make your analysis harder to make and one of the basic principles of Data Visualization is to get your message across as easily as possible.
2. Do not use a pie chart if you have a high number of elements to represent
Another common mistake is when many elements are represented in a pie chart. Going back to the principle enunciated before — getting your message across as easily as possible -, you can already understand why this is a mistake and a practice that you should avoid. Referring to the example above, a high number of slices makes the reading and the analysis of the graph very hard, which is definitely something that you do not want. There is no such thing as the right number of slices that a pie chart should have but, as a rule of thumb: if your chart will have more than 5 slices, you should start considering another option.
3. Do not use a pie chart without scale/data labels
The human brain is not great at comparing the size of angles neither at reading values accurately without a scale, which is very problematic as mistakes can arise from there. It can happen if you are a consultant at a large firm and your team is overloaded with work as the deadline approaches, or even if you are solving a Finance case. We, humans, are very good at making mistakes, so try making your life easier and make avoid those mistakes by, either not using a pie chart, or, if you really want to use one, do not forget to add the scale or data labels. If you look at the pie charts and the corresponding bar charts, it is very hard to tell which slice is bigger but is super easy to look at the bar chart and compare the size of the bars.
4. Do not use 3D pie charts, ever. Seriously!
In addition to everything that was already mentioned, 3D pie charts can make everything worse. One of the most commonly used examples is when Steve Jobs is presenting the U.S. smartphone market share at MacWorld in 2008. Although six slices is one more than the “recommended” number of slices, it is acceptable. However, there are positive points to note: all slices have data labels and they are ordered from the biggest to the smallest (naturally, the “Others” slice must come at the end, even if it represents a bigger value than any of the previous slices). However, if you are not paying much attention and just take a glance, it seems that Apple’s 19.5% are way closer to RIM’s 39%, when, in fact, Apple’s market share was half of RIM’s!
Before finishing this article, you CAN use pie charts! In order to make them the right way, follow these 6 tips:
- The data to be represented must be a percentage breakdown
- Each slice represents part of the 100%
- Order the slices by size for the analysis to be easier
- Use a pie chart if you have 5 slices or less
- Add a scale or data labels
- Do not make a 3D pie chart
I hope this article has taught you something and that you can use pie charts correctly!
By Miguel Bezerra
