Dear Paul,
Alan Zaslavsky has explained why statisticians avoid pie-charts,
especially exploded ones like yours!
A further problem is whether the segments remain distinguishable when
copied in black and white. In a bar chart they would be.
However I like the feature of taking one segment and dividing it into
component parts. Is the area of the sub-pie-chart equal to the area of the
segment?
In fact a bar chart (with a sub-bar-chart) would have provided the same
information more clearly. Alternatively the custodial bar could be divided
into sections representing prison, youth custody and other. I would try
both and decide which provided the clearer message.
Aesthetically bar charts are often drawn too large and look ugly but
thinner bars and making it no larger than necessary for clarity can help.
The pie chart has two possible advantages: it looks prettier and it
emphasises that the segment represents a proportion of the whole! (The
latter is relevant as often it is hard to discover the denominators of
quoted percentages!)
I would not forbid pie-charts, just encourage people to make them flat and
to consider alternative presentations of the information. Sometimes a
table is all that is needed!
Jane
--
Mrs Jane Galbraith
Honorary Research Associate
Department of Statistical Science
University College London
Gower Street
London WC1E 6BT
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>>>>>>
> I don't use pie charts very often, but they have their place. Here's
one
> I made a long time ago - - it helps to make a couple of simple points
visually.
>
> Paul Spicker
>
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