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The Café Wall Illusion in a Bar Chart

The Café Wall Illusion makes you to see perfectly parallel lines as being at an angle. It's a curiosity and a cool perceptual illusion – except when it shows up in a bar chart, as it did in this example.

The classic café wall illusion was first spotted on a tiled wall, where the misaligned black and white tiles were making the lines look all wonky (image from Wikipedia).

cafe-wall

FiveThirtyEight journalist Allison McCann recently tweeted this image, which also shows the illusion. This is the first time I've ever seen it in a bar chart.

It looks like that zero line is angled up slightly. I wonder if this would cause people to be slightly biased in their reading of the data.

Posted by Robert Kosara on June 30, 2016. Filed under Perception.