Friday, February 17, 2012

Lying with pyramids

Blogging pace may be slow, as I am busy and/or just not investing the time.  So here's a short one.

This image was taken from Facebook, from the Being Liberal page.

There is a special place in math hell for people who use pyramids (or similar 3D objects) to represent percentages.  Observe, on the left, meat and dairy makes up 73.8% of the height of the pyramid.  But it takes up 98.2% of the volume.  This is because the base of the pyramid contains greater volume than the tip.

It's a classic way to lie with graphics.  It makes percentages appear different from what they really are.  I could have made a graphic with the order reversed, and it would lie in the opposite direction.
Or I could have just used a bar graph, as would have been appropriate.

I wasn't going to comment on the content of the graph, except that that is a lie too.  Those are not the Federal Nutrition Recommendations, not since 2005.  The old food pyramid was replaced in 2005, and replaced again in 2011.  This seems to be an oversight rather than an intentional lie, since I think the new recommendations are even more different from the subsidy percentages.

There are probably other problems with the graphic too, but I leave those as an exercise to the reader.