Misreading misleading charts: entrepreneur edition

June 18, 2009 in Math

Paul Kedrosky writes about a study on the rate of entrepreneurship among various age groups, which includes the following piece of junk (ch)art:

Why is this chart 3D? It contains information in only two spatial dimensions (time and rate), with a third dimension coded by color. To make the chart itself is a purely superfluous move - in fact, it's worse, because it distorts the graph.

One of the points of the study is that the rate of entrepreneurial activity is much lower among young people than older people. Thus, in the chart above, the blue line should be lower than the other lines. However, the forced perspective of the 3D chart makes the blue line appear even lower than it really is. For example, if all age groups had rates of 0.27% in 1996, then the blue line would print physically lower on the page than every other line despite having the same value.

Adding an extra dimension when it is unnecessary is a serious charting mistake. Adding an extra dimension beyond what your medium (in this case, a 2D screen) is capable of displaying requires serious justification. In this case, it adds nothing and even detracts from one's ability to read the graph.

Of course, it does so in a way that enhances the study's point (that blue line is REALLY low!). Perhaps the third dimension wasn't added solely for visual effect, but for suggestive purposes as well?

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