Mistakes, we’ve drawn a few

At The Economist, we take data visualisation seriously. Every week we publish around 40 charts across print, the website and our apps. With every single one, we try our best to visualise the numbers accurately and in a way that best supports the story. But sometimes we get it wrong. We can do better in future if we learn from our mistakes — and other people may be able to learn from them, too. After a deep dive into our archive, I found several instructive examples. I grouped our crimes against data visualisation into three categories: charts that are (1) misleading, (2) confusing and (3) failing to make a point. For each, I suggest an improved version that requires a similar amount of space — an important consideration when drawing charts to be published in print.Let’s start with the worst of crimes in data visualisation: presenting data in a misleading way. We never do this on purpose! But it does happen every now and then. Let’s look at the three examples from our archive.This chart shows the average number of Facebook likes on posts by pages of the political left. The point of this chart was to show the disparity between Mr Corbyn’s posts and others. The original chart not only downplays the number of Mr Corbyn’s likes but also exaggerates those on other posts. In the redesigned version, we show Mr Corbyn’s bar in its entirety. All other bars remain visible. (Avid followers of this blog will have seen another example of this bad practice.) Another odd thing is the choice of colour. In an attempt to emulate Labour’s colour scheme, we used three shades of orange/red to distinguish between Jeremy Corbyn, other MPs and parties/groups. We don’t explain this. While the logic behind the colours might be obvious to a lot of readers, it perhaps makes little sense for those less familiar with British politics.

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