Dear Robert,
> I don't think I've used pie charts, except perhaps when showing how
> wealth is divided, where 'slices of the pie' make some sort of sense.
> But I get the feeling from some of the exchanges (Jane Galbraith for
> example) that pie charts are not much loved by statisticians. Is
> there a technical reason for this? Whilst I don't find them very
> useful, the kids are obviously drawing pie charts at school - on
> every topic - what should we say to teachers if we wish to discourage
> this?
The following link might be interesting for you:
http://seedmagazine.com/content/article/getting_past_the_pie_chart/
"Playfair rightly intuited that visual representations of data can
enable people to make comparisons more easily. Many psychoperceptual
studies have explored the human mind’s aptitude for gleaning
information from pictures. Unfortunately, the pie chart incorporates
tasks that we humans systematically fail to perform accurately, all
those exercises that come at the bottom of the hierarchy of perceptual
tasks, formalized by Cleveland in a landmark 1984 paper. So although
we’re good at comparing linear distances along a scale — judging which
of two lines is longer, a task used in bar graphs — and we’re even
better at judging the position of points along a scale, pie charts
don’t bring those skills to bear. They do ask us compare angles, but we
tend to underestimate acute angles, overestimate obtuse angles, and
take horizontally bisected angles as much larger than their vertical
counterparts. The problems worsen when we’re asked to judge area and
volume: Regular as clockwork, we overestimate the size of smaller
objects and underestimate the size of larger ones, to a much greater
degree with volume than with area."
(Source:
Understanding the shortcomings of the pie chart can help us
make sense of and improve the emerging scientific aesthetic of the 21st
century. Getting Past the Pie Chart
Universe in 2009 / by Veronique Greenwood / February 18, 2009)
Best wishes
Micha
--
"I keep saying the sexy job in the next ten years will be
statisticians. People think I’m joking, but who would’ve guessed that
computer engineers would’ve been the sexy job of the 1990s?" - Hal
Varian, The McKinsey Quarterly, January 2009
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