RE: [S] Pie Diagrams

Gunter, Bert (
Fri, 13 Nov 1998 09:40:00 -0500

Dr. Garrett:

It is wonderful to hear from a REAL scientist with REAL scientific problems.
Thankyou for your note to s-news. I hope that it encourages other silent
scientific readers to speak up!

May I suggest an alternative display that might do better than your pies,

At each location display the following small rectangular graphic:

The left part of the graphic is a narrow fixed width bar whose height
represents the total mineral weight at the site. Hence comparing these
heights by eye gives a more accurate and still geographically located view
of the total weights than comparing circles (whose sizes we judge as areas,
not diameters, so it is important to encode the total as sqrt(diameter) not
diameter, even in the pies).

(Clearly separated with a small break or vertical line), the right part of
the graphic (perhaps in a different color, though this is not necessary)
consists of a (filled?) curve: The "x-axis" is simply the first 5 different
minerals, always in the same order of course (the 6th is redundant, but you
could include it if you wanted). The height at each mineral type is simply
the proportion of minerals at the site. The curves give a more accurate and
easier to perceive view of the mineral "profiles" both because it is easier
to make comparisons on a fixed linear scale and because the positions of
each of the mineral proportions in the graphic do not vary from site to site
as they do for your pie chart; changing positions makes it more difficult to
make comparisons (that is why you have to add color cues -- but color cues
are always problematic because we perceive different colors differently. One
slice may look bigger simply because it is a different color).

So not only can you do better than pie charts, you also don't need colors
(not everybody has color copiers yet!). Of course, there may be times when
pie charts are the best solution, but I don't think this is it, yet.

Again, I appreciate your writing in. I always find honest science
more interesting than complex statistical ruminations.

> Bert Gunter
> Biometrics Research RY 70-38
> Merck & Company
> P.O. Box 2000
> Rahway, NJ 07065-0900
> Phone: (732) 594-7765 Fax: (732) 594-1565
> "The business of the statistician is to catalyze the scientific learning
> process." -- George E.P. Box
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