Basketball Statistics Blog

STATISTICS LIES

Uses and Misuses of Statistical Graphics:

Yesterday, with the last exposition at the eBA 113 Basketball Statistics Register Course we were discussing the topic of the statistics lies which was initiated by the exposition "Statistics & Statisticians" at eBA ONLINE.
Here is the opinion of Paul H. Kvam and Joel Sokol from their work "Teaching Statistics with Sports Examples":
Statistical lies are most frequently committed in graphical form, where the eyes can be more easily deceived by spurious trends suggested in a picture. A common abuse is manipulating scales on charts and graphs by truncating, censoring or transforming the axis values.

The next figure shows two different charts showing an increase in average attendance at NCAA Women's Soccer games between 1998 and 2003. The first (blue)chart  is the default Microsoft Excel chart; many statistical software packages, in fact, will restrict both axes to a small set of values that contains the data, which helps the reader focus on chart differences more clearly. However, it also removes the scale of difference from the picture, which has potential to mislead readers who pay little attention to the axis labels.

Two different charts showing average attendance
at NCAA Women's Soccer (season) matches

The reader's sense of proportion can be manipulated further with image-based charts, which are standard in sports publications. As an example, the figure below graphs the season wins for the New England Patriots using clip-art in place of vertical bars.

Regular season wins for the New England Patriots, 2002-2003

While the height of the football icons corresponds to the information the graph is meant to communicate, the size of the footballs does not; the Patriots improved 56% in wins between 2002 and 2003, but the increase in area of the football icons is over 140%.

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