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Misleading graph from the news

There are tons of examples of statistics being misused or misrepresented by the media and politicians (among others). I'm going to try and collect examples as I find them so that I don't have to search for them at the last minute.

I saw this image floating around the internet (not sure who originally took the screenshot):

This graph is misleading because it exaggerates the resulting increase in tax rate by not showing having the Y-axis display zero. Displaying the graph only from 34% and up makes the tax rate after January 1, 2013 to be 5.6 times what the rate currently is. In fact, the actual tax rate after January 1, 2013 is about 1.13 times what it currently is if the Bush-era tax cuts are allowed to expire. This is what a more accurate graph would look like:

The graph now starts at 0% instead of 34%.

Disturbingly, when I went to make the above in LibreOffice Calc the default scale was 32-40% (same in Microsoft Excel). While there are times when displaying zero is not necessary, not including zero magnifies the relative differences among the categories (Lemon & Tyagi, 2009). Kozak (2011) gives some recommendations about when including and excluding zero is appropriate; essentially, if zero is meaningful in the context of the data it should be included.

  • Kozak, M. (2011). When should zero be included on a scale showing magnitude? Teaching Statistics, 33(2), 53–58. (link to abstract)
  • Lemon, J. and Tyagi, A. (2009). The fan plot: A technique for displaying relative quantities and differences. Statistical Computing and Graphics Newsletter, 20(1), 8–10. (link to full article) [Note: I don't know if this article is peer-reviewed, but it is a publication of the ASA, so there is some weight to it.]

One Comment

  1. [...] individual examples of statistical things - I get a good number of hits from people searching for misleading graphs in the news, and I'll try to keep posting things that people are looking for. This is an audience that I wasn't [...]

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