12 October 2013

How to Display the Data

How many times have you heard your professor or your boss saying “where are the numbers supporting your statement?”. I bet it has happened many times. Probably your professor or your boss was right. You often need to support your case by showing some data.
However, most presenters show the data without asking themselves whether or not their audience will actually be able to see it and understand it. They do it just to prove they have done some homework without having the audience in mind. The result? Incomprehensible data displays. But if the data you show is incomprehensible, you are incomprehensible too and this is something we all want to avoid. The purpose of this article is to make you aware of how to display the data during a presentation in a way that is meaningful for your audience.

First of all, you need to understand what the purpose of data displays is in a presentation setting. The purpose of a graph is to show quantitative relations, not precise values. If your goal is to show precise values, a table might be more appropriate. Therefore, different data requires different formats:
  • Tables should be used when the aim is to show specific numbers
  • Graphs, such as bar graphs, can be useful to make comparisons
  • Line graphs are best for displaying trends
  • Pie charts are also good for making comparisons, but only if you have to compare few values
There are two essential principles you should be aware of when presenting data: reduce and emphasise.


Graphs themselves can be hard for the audience to understand, so if you add decorative elements such as company logos or other extras you are doing nothing but making it even more complicated for your audience to understand. Your job is instead to help your audience understand the data you are showing. To do that you should avoid creating noise, that is, you need to include as much as necessary, but not more. The effectiveness of your quantitative display mainly depends on your decision about what to include and what to exclude. Graphs, charts and tables can become much more effective and easier to understand if you only reduce the nonessential. Here I am not talking about removing important elements, but only the nonessential. The problem is that what most people think is important showing in a presentation is actually not. So the next time you design a graph for you presentation, ask yourself two questions:
  • What is the essence of the point your graph is intended to make?
  • Are there any nonessential elements that can be reduced (better yet, removed)? 

In this slide there is too much clutter. The image of the map does not add anything to the core message. Nor do the date and the page number at the bottom. Also, numbers are too small to be seen and colours have not been chosen purposely.


This is a remake of the previous slide. Only the essential information is displayed, figures are visible and can easily be associated to the respective country.


To emphasise means to make it clear for the audience what the most important point is. There are basically two ways to achieve that:
  • You can use contrastsuch as colourto highlight the most important bit of your data display
  • You can also write a statement rather than a title
This presentation is about The Bahamas, that is why I have highlighted The Bahamas in red. Also, instead of using a general title, I used a direct statement to make it clear what I was talking about.


Pie charts
I don’t fancy using pie charts because we are not very good at accurately grasping the differences in size among the slices, especially when those are very thin due to the fact that the values you want to compare are too many. In this case it is better to use a bar graph. But if you really want to use a pie chart, keep this in mind:
  • Do not use 3-D effects. This is actually a general rule which applies to the design of any kind of graph. Never use 3-D effects to show two-dimensional data. It is not only aesthetically unpleasing, it does not make sense from a “mathematical” perspective either.
  • Do not use a legend. Rather, put labels inside the slices.


Bar graphs
Bar graphs are best for making comparisons among values. You can use vertical or horizontal bar graphs almost indifferently. Only be careful with the number of values to be compared. When they are quite a few, I would recommend to use a horizontal bar graph in order to avoid setting the labels on the x-axis at an angle. Examples are shown above.

Line graphs

Line graphs are good at showing trends over time.

Now the question is, why do most presenters not follow those basic guidelines? According to me there are two main reasons. The first one is that they are not aware of them, the secondand most important oneis that they are afraid of simplicity. People confuse simple with simplistic. Making data displays simple is not about excluding important information. Rather, it is about showing the essential information without clutter or extra decoration in a way that is clear and meaningful for the audience.

Finally, let me tell you something. Do not confuse slides with documents. If you have detailed and complex data that is absolutely necessary for your audience to see, then create documents and hand them out. It is okay not use slides, you don’t have to use slides all the time. You might mix your presentation with slides when appropriate and handouts when you need to show detailed information. But when you do use slides, I suggest you to practise reduction, emphasis and to choose the correct chart.


Where do you want to be?

The ideas in this article have mainly been collected from the book Presentation Zen by Garr Reynolds (chapter Simplifying the Data)