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   04/4/2008 4:30 PM


        Horizontal Panel Dot Plot

Gary Klass (Illinois State University) has an excellent post on Constructing Good Charts and Graphs. He has a very informative discussion on pie charts; several of his points are well worth repeating:

  1. "...multivariate comparisons provide for more meaningful analysis than do single variable distributions ..

  2. ".. pie charts should be rarely used, if at all"

  3. "3D pie charts are even worse"

  4. "Forcing the reader to draw comparisons across two pie charts is also a bad idea"

  5. "All the information in ..pie charts ... can be conveyed more precisely ... in a simple bar chart."

Excel provides both pie and doughnut charts. Data visualization problems associated with pie charts also apply to doughnut charts.

Excel users have alternatives to pie/ doughnut charts. Dot plots can be much more effective. Panel dot plots like the chart on the right can be used to show changes over time with small multiple -  trellis like displays using Excel charting, data transformations and dummy axis techniques explained in this site.

The panel dot plot chart (above -  right) shows the distribution of proved world oil reserves by  region for 1984, 1994 and 2004 from data in the BP Statistical Review of World Energy - 2005. 

The initial version of this chart was prepared using 3 doughnut charts, one for each year.  (click thumbnail to see BP's original chart). 

This workbook download  shows you how to make panel dot plot charts in Excel.