st: The not so humble pie

[Ronan Conroy <rconroy@rcsi.ie>]

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



Ronan Conroy
=================================

rconroy@rcsi.ie
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?)
http://rcsi.academia.edu/RonanConroy

P    Before printing, think about the environment





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