During President Obama's State of the Union speech on Tuesday night, the live feed at the White House website featured PowerPoint-style infographics and bullet points to accompany the President's statements. One of those charts was a comparison of the GDP of the United States and its nearest rivals:
Notice anything odd? The 2010 GDP of the US isn't quite three times that of China, but you could easily fit four of those China circles in the US one, if not more. In fact, the area of those circles are proportional to the square of GDP, as Dan Meyer illustrates with amusing snark. Scaling a variable to one dimension (here, diameter) of a two-dimensional shape is a rookie mistake in data visualization, an issue Edward Tufte popularized in his book The Visual Display of Quantitative Information. And given that Tufte was recruited by the White House to improve communication about data that chart is, well, a bit embarrassing.
But even when the area of is appropriately scaled, circles are still a poor tool for communicating information about numbers. Pie charts are circles, and it's well known that pie charts suck when it comes to comparing proportions. And even simple circles are hard to compare, as amply demonstrated in this demonstration from the blog Contrast:
"If you could have the profits of company A, or those of B,C,D,and E combined, which would you take?"
The answer is that the area of A is greater than that of B, C, D and E together, but that's hardly apparent to my eye. The whole post is well worth a read -- it's chock filled with examples of good and ba data visualizations -- and a fine testament to the principles of Tufte.
Constrast: Infographics and Data Visualisations (via)
It's been quite a while now since Tufte published his books on data visualization and misleading diagrams.
Are the President, Vice-President, and advisers, such nincompoops that they do not even read the visual they are presenting to the American people (and the world). Or, are they deliberately trying to mislead?
My guess is that politicians, like many of the people they represent, are walking around half asleep, mouthing platitudes, and not taking the time to think.
Posted by: Republic of Mathematics | January 29, 2011 at 06:42
This might be a rookie mistake but has anyone considered that it was done deliberately to exaggerate the importance of the USA's GDP?
"Look how much bigger our balls are than China's"
Posted by: Philip Hodges | January 31, 2011 at 05:39
Also, the 3D rendering on the circles (spheres?) results in fuzzy edges on the circles. To me, it's hard to see that China's circle is larger than Japan's. Only after magnifying the image 400% did I convince myself that China's was, indeed, larger.
It is so much clearer to compare the economies by using a horizontal bar chart :
barplot(c(2.5,3.3,5.3,5.7,14.6), horiz=T, names.arg=c("France","Germany","Japan","China","US"))
Posted by: Rick Wicklin | January 31, 2011 at 07:00
I think the post is very good ,you look at it ,and you?
Posted by: ray ban sonnenbrille günstig | August 04, 2011 at 19:37