Two easy pieces
Dissecting two axes

The redundant dimension eye-trick

My friend Patrick was particularly incensed by this chart, from the Economist publication "The World in 2006", which has been discussed here and here.  It employs a typical trick to make charts more "entertaining", that is, introducing an extra dimension, region of the world in this case.  As the right-side junkart version shows, collapsing this dimension results in a much clearer graph.  Disagree?  Try figuring out which columns to contrast in the left chart, and you might get dizzy as if reading an Escher "impossible trident" (more Escher goodies here).

Redogdpgrowth

Reference: "Wider but not deeper", The World in 2006.

Comments

John S,

This is a case where the use of color might be helpful. I realize the crosses are the European area and the dots are the U.S., but it's still somewhat difficult to make out. Maybe make one line blue and the other red?

Kaiser

I have a love-hate relationship with colors. I like sparing use to make specific points; this particular case could count as that.

That said, it is easy to abuse colors. Also, while we still have lots of grayscale printers and copiers in use, I tend to err on the safe side.

And diverging even more... I like the feature in PowerPoint where you can preview what a slide looks like in grayscale. I love this feature although I don't make use of it much. I don't know why.

Andrew Gelman

I agree on the colors. Also I'd alter both axes:

x-axis: Just put labels at 1995, 2000, 2005. This gives a better perspective on the time period. (It would be even better to go back another 10 yrs or so.)

y-axis: Again, no need to label all those tick marks. I'd just label 0, 2%, 4%.

Also, I'd extend the y-axis just a bit below zero (with a dotted line at the reference line of 0). I say this because GDP growth can be negative. The "hard boundary" at 0 in the graph gives the implicit visual impression that y can only be positive.

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