The Secret Axis

Gary Smith’s advice on statistics, Standard Deviations, is a really useful and entertaining book. He points out a number of major problems with the way stats are used. Some problems arise from deliberate tricks played by researchers/managers describing data. Other problems arise through carelessness; the researcher/manager using the data doesn’t realize they are abusing the data. Over the next few weeks I’ll examine three problems that Smith highlights.

One of the problems Smith describes comes from the way that data is visualized. He makes a host of scathing and funny comments about data presentation. I liked his description of “The Secret Axis” (Smith, 2014, page 73) which is something I often see in graphs. (Technically something I don’t see given it is a missing axis).

Smith gives high profile examples of abuse of data visualization. In 1982 Ronald Reagan presented his budget plan with no numbers on the Y-axis; the viewer couldn’t know the scale of what was being presented. A 9% difference in tax plans was represented as a 90% difference on the (unspecified) Y-axis. The quote from David Gergen, Reagan’s spokesman is fantastic. ‘”We tried it with numbers and found they were very hard to read on television so we took them off”‘ (Smith, 2014, page 74). Let us be (very, very) generous and assume that Gergen made a mistake that just happened to make his boss look better.

The lesson is that we all need to be careful about the way we present data. We don’t want to leave anyone with a false impression because of our secret axis.

Conversely when confronted with a secret axis don’t accept it. A graph without a clear axis is merely a pretty picture and shouldn’t be treated seriously.

Read: Gary Smith, 2014, Standard Deviations: Flawed Assumptions, Tortured Data and Other Ways to Lie With Statistics, The Overlook Press.