11/11/06 - Uses and Misuses of Statistical Graphics:
Nowadays we are discussing the topic of the statistics lies at our forum 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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