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Re: st: RE: The not so humble pie


From   Jeph Herrin <junk@spandrel.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: The not so humble pie
Date   Wed, 21 Oct 2009 14:05:05 -0400


Another defense of the humble pie chart (speaking of children):

http://tinyurl.com/yjv3dqr

Jeph


Nick Cox wrote:
Thanks for the thanks.

Being rude about pie charts is all good fun and, for many of us, an
acceptable variant on blood sports. But if precise decoding of
proportions is the aim, then tables beat pie and bar charts hand
down, or the actual numbers can just be added to the graph!

One major objection to pie charts is that their effectiveness breaks
down very rapidly as displays depart only slightly from extreme
simplicity. You need only think about comparing 30 category
proportions across 3 pie charts, or 10 categories across 10 pie
charts, to realise that.

Irrelevantly, but it just sprang to mind: Some of you may enjoy this
algorithm, probably known throughout history, for sharing a pie
(cake, whatever) between two children. One child gets to cut and the
other gets to choose.

Nick n.j.cox@durham.ac.uk

Ronan Conroy

As well as a thank-you to Nick for his very useful wrapper to Stata's
 rather awkward -pie- command, -pieplot-, I thought I might share an
 interesting paper which illustrates the history of this humble graph
 and reviews the evidence for its supposedly inferior performance to
 the bar chart.

The author concludes:

There seems to be little objective basis for a prejudice against the
 pie based on considerations of speed or accuracy of estimation—the
 pie chart does as well, if not better, on simple tasks such as the
estimation of a single proportion or the com- parison of a small number of proportions. On the other hand, the natural competitors of
 the pie suffer significant disadvantages. For example, the simple bar
 chart does not provide an integrated representation of the whole,
thus making part–whole estimation more difficult. This drawback may be
alleviated by providing a reference bar, but the individual proportions will be at varying distances from the reference bar. The
 divided bar chart does provide a pictorial representation of the
whole but it is less desirable than the pie for exactly the same
reason that instru- ments that have circular dials (speedometers,
altimeters, airspeed indicators, clocks, etc.) are generally
preferred to those that use linear representations—they take up less
space while providing the same or better resolution. Finally, the pie
provides at least five natural anchors (0%, 25%, 50%, 75%, 100%)
compared to only two, or at most three, for the divided bar (0%, 50%,
100%). A bar chart —without a reference bar—affords no natural
anchors to assist in the accurate estimation of proportions

http://www.psych.utoronto.ca/~spence/Spence%202005.pdf


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