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st: The not so humble pie

From   Ronan Conroy <>
To   "statalist hsphsun2. harvard. edu" <>
Subject   st: The not so humble pie
Date   Wed, 21 Oct 2009 17:24:45 +0100

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

Ronan Conroy
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)

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