Gelman remakes a grouped bar chart
Light entertainment: impossible is nothing!

More illusions

A reader sent over another example of an optical illusion that chart designers should think about. Here's a 3D column chart:

And the illusion:



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I don't get it. What's the illusion? And what does it have to do with the chart?


I don't get it either. But I'm glad someone else is with me on this :)


Maybe the illusion is that the front and back bars are actually the same height but we think the back one is taller.


Think its the fact that in the top illusion, as there are only two lines, its clear that the top and bottom one line up (apart from the break in the middle due to the white area), however, in the image below, with two lines below the white area, its not easy to tell which of the two lines line up with the one above.

The eye isnt good at picking up small differences of this sort


Exactly. Looking at the chart, are you able to tell whether the purple bars are the same height or if the front one is shorter than that back one?

John Sheldon

I am very thankful to all your team for sharing such inspirational information.

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