Communicating data effectively with data visualizations—Part 19 (Doughnut charts)

INTRODUCTION

When comparing proportions or prevalence, the pie chart has been used as a favorite among Excel users due to its ease and familiarity. However, Tufte and other data visualization pioneers lament its use and recommend other graphical representations as alternatives.1 Doughnut charts are similar to pie charts except that the center is removed. Unlike pie charts which do not provide a good comparison of the proportional slices to one another, the doughnut chart focuses on the use of the length of the arcs for comparisons, which limit the potential for errors. By comparing the arc’s length of a doughnut chart to each other, you avoid the problem of comparing proportions between the slices in a pie chart.

 

MOTIVATING EXAMPLE

We will use data from the Centers for Disease Prevention and Control (CDC) to illustrate the number of tobacco products used among Middle and High-School students in the United States. You can download the Excel document here.

Source: Flavored Tobacco Product Use Among Middle and High School Students—United States, 2014–2018. url: link [Accessed on 17 October 2019]

Source: Flavored Tobacco Product Use Among Middle and High School Students—United States, 2014–2018. url: link [Accessed on 17 October 2019]

In 2018, there were 73.98 students per 100 population who reported using e-cigarettes. This was followed by a vastly lower prevalence of 28.66 students per 100 population who reported using Menthol cigarettes and 26.63 students per 100 population who reported using cigars. The CDC undertook this investigation to assess the types of tobacco products used by students. Based on this data, e-cigarettes appears to be a popular tobacco product. 

We will generate a doughnut chart to illustrate the prevalence of different tobacco product use in students.

CREATING A DOUGHNUT CHART

We want to create a side-by-side comparison between the different types of tobacco use in students using the prevalence, number of students per 100 population. This will allow us to make easy comparisons using the circumference of the doughnut charts.

 

Step 1. Set up the data

Since the prevalence is the number of students per 100 population, we can define our denominator as 100. Therefore, if 73.98 students reported using e-cigarettes, then 26.02 students did not (100 – 73.98). The table below provides the calculations to estimate the remainder column.

Figure 2.png

Once the remainder column has been calculated, we can Insert the doughnut chart onto our Excel worksheet.

Step 2. Insert donut chart

Select the prevalence and remainder data for the e-cigarette row.

Figure 3.png

Then Insert the doughnut chart using the Excel ribbon.

Once you select the doughnut chart, Excel will generate a default chart for you.

 
Figure 5.png
 

Step 3. Change the size of the doughnut chart

The default size is not balanced. We want to make the height and width the same size. To do that, we start by clicking on the Format tab and then going to the dimensions box to change the defaults to 4 inches by 4 inches.

Step 4. Change the size of the doughnut ring

The current doughnut ring is too thin. We can change this by right-clicking on the doughnut and selecting the Format Data Series. It will open a window with options to modify Doughnut Hole Size. Change this from the default to 65%. 

Step 5. Add data labels

To add data labels, right-click on the doughnut and select Add Data Labels. The data labels will populate both segments of the doughnut.

Step 6. Change font size and color palette

We can improve the aesthetics of the doughnut chart by increasing the font size and changing the color palette. In this example, I changed the font to Arial size 14 and I used the Blue Monochromatic Palette #1.

 
Figure 9.png
 

Repeat this for the other types of tobacco use and you can generate a series of doughnut charts that are easily comparable to each other.

CONCLUSIONS

Doughnut charts are better alternatives to pie charts because they use the arc of the circle to represent the proportion of the population. You can navigate through the differences quickly with the doughnut charts and see how different the prevalence of e-cigarettes are compared to other forms of tobacco use. This indicates that there is a huge popularity among students to use e-cigarettes as a favorite tobacco product. The implications of students using e-cigarettes let along any type of tobacco products are under investigation, but the data reported here highlight the popularity of e-cigarettes among students in the United States.  

 

REFERENCE

  1. Tufte ER. The Visual Display of Quantitative Information. Second. Cheshire, CT: Graphics Press, LLC.; 2001.