Displaying data: Bar charts

So you have a mountain of data and you want to display it?  Don’t quite know what to use? Do not despair, in the future i have decided to dedicate at least one post a week, maybe more sometimes, on “Displaying data”.  Today I want to share a couple of thoughts on bar charts.

Two basic types of bar charts. Horizontal and vertical. (OK I realize some would call vertical bars columns, but for me they are roughly the same. Roughly, you said? Yes, they can show the same kind of data, but sometimes should not!

Vertical bars tend to be read from left to right, and ones brain can be fooled into thinking its a time line…  With horizontal bars that danger disappears. Oh, come on! That is being ridiculously fidgety you may say.  Well consider the following bar chart, with vertical bars.

Note how you need to look twice not to see a progression from left to right. So maybe you wanted to show which product we sold most of…  It still will kind of work.

However, if you wanted to show sales growth relative to product, you would have failed miserably.  You left it open to the viewer to do some calculations – and the average viewer would have to do a lot of processing to figure out that Prod B grew percentage wise the most!  The following graph can serve as a better example.

What is the lesson(s) to learn from this example.

  1. Figure out what you want to say, i.e. what is your message. In other words what do you want the audience to see. (In the example: Biggest growth percentages)
  2. Do not be scared to transform the data into a useful format (In the example: compute the %growth)
  3. Show (only) the data you want them to see. Anything else confuse the message and make people think about something else but your message…

Finally I’d like to point one more thing out which has got little to do with the bar chart per se, but more with its use in the presentation.

  1. Change the title of the graph to the message.
  2. Highlight the data you want the audience to see.

Applying the above will yield the graph below: a far cry from the first graph.

The moral of this post. Think what you want to share with your audience and make sure that you share that and nothing else…

In the future I will look at stacked bar charts and some other forms of charts.

What do you think?


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