The racetrack graph
Dec 14, 2005
A reader, Nick, sent in this fantastic example of chartjunk. It is an absolute classic. He points out - as have we here - that a simple table works better.
We shall call this genre "racetrack graphs". If Italy and Japan both traversed 20 metres in distance, it'd appear as if Italy's curve was longer than Japan's because Italy has the inside track! This bias is well known to anyone who has run track.
The way this chart is constructed is to have length of curve proportional to angle, not distance (see below left); however, our eyes are naturally drawn to the circumference! When we see Japan's green line, we perceive the length of the line, not its angle. In particular, notice that the large separation between Canada and Japan represents a 19% difference, which should be double that between Italy and the vertical line (below right).
Nick has a few other examples at his site. Well worth a look!
And thanks to Jef (see comments) for pointing out my subtraction error. I will correct the graphic later. (12/14/05, 10 am) Graphic corrected. (9 pm)
I agree that the racetrack is misleading, but the difference between Canada and Japan is actually 19%, so it isn't quite as bad as it looks. Eyeballing the Italy to vertical gap which is 10%, it looks like the difference between Canada and Japan is closer to 30%, which is still a lot more than 19%.
Posted by: jef | Dec 14, 2005 at 08:47 AM
Is there a way to contribute a bit to the cause of the Christmas wishlist? I would be happy to kick in $5, but a whole book is a lot.
Posted by: AM | Dec 14, 2005 at 12:52 PM
AM - I'll look into it. Thanks for offering.
Posted by: Kaiser | Dec 15, 2005 at 11:42 PM