Saturday, 24 March 2012

Beware of the bubbles

This morning I came across this >article

I find it difficult to believe that an organisation so intrinsically linked with data as Nelsen can fall into one of the biggest visualisation traps around. Their site states, “We believe providing our clients a precise understanding of the consumer is the key to making the right decisions.” I seriously doubt any reader of the following diagram will receive an accurate impression.

Take a moment to compare some of the numbers shown with the circles presented. Do you get the impression that for TV Shows the blue circle is 4 times the size of the orange one? It’s unlikely, because the designer in this case has scaled the circles using their diameter values. There is no escaping the fact that the brain will naturally try to compare their areas, thus it is necessary to take square roots of the data beforehand. Some alternatives to the Downloaded Music part are shown below.

In fact the area method is far from perfect, notice how difficult it is to compare values of 19 and 20? Had the percentages not been shown we may have assumed they were identical. The bar method is far superior for communicating quantities precisely. Chapter 1 of my dissertation from last year examines this in greater detail.

Dissertation >here

Nelsen are currently running a data visualisation competition, unfortunately only residents of the United States are permitted to enter. Nonetheless I await the results with bated breath.


  1. Fantastic. Excellent write-up. It's so obvious! I'm surprised this got published.
    I wonder if they didn't know how to calculate the area of a circle, and couldn't be bothered to find out. Or just didn't see that this method was so wrong.
    Maybe they were aiming for distorted results…

    1. Perhaps this is what they do with their work experience students?

  2. Very nice article and examples.
    I will study your dissertation.