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grasshopper

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Reply with quote  #1 
I guess it is accepted (or at least argueable) that it's ok to use a pie chart to compare a single value to the whole.

But is a multi-slice pie ever acceptable?

Hmm (or should I say Mmmm), maybe in this particular case?  ;)

Pie pie chart
sfew

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Reply with quote  #2 
This delicious-looking graph nicely illustrates one of the perceptual problems with pie charts. Notice how the Lemon Meringue and Pecan slices appear as large or larger than the Apple Crumb slice, even though they're the same size in the first case and smaller in the second. Assuming that these slices accurately represent their percentage labels, this misperception is probably caused by the position of the text labels relative to the borders of the slices. Because the label "Apple Crumb" comes closer to the radial borders of its slice than the label "Pecan" comes to its borders, the Pecan slice appears larger because its label fills it less, even though the two slices are the same size. Although the Lemon Meringue label is larger than Apple Crumb, its orientation relative to the slice places a greater distance between the left edge of the label and the outer borders of the slice, which makes the slice appear less filled and thus larger than the Apple Crumb slice.

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Stephen Few
grasshopper

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Reply with quote  #3 
Hmm... I'm not sure I agree.  I have no problem determining which slice is bigger/smaller, but maybe that's because I know that the slices are ordered clockwise, largest-to-smallest.

sfew

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Reply with quote  #4 
It's certainly possible that our perceptions would differ, even if you were able to ignore the fact that the slices are ordered by size and based your judgment on visual perception alone. It would be interesting to order the slices of this pie chart randomly to see if that altered your perception, but it would be more work than it's worth to do this without altering any other aspect of the chart.

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Stephen Few
grasshopper

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Reply with quote  #5 

Yes - if they were randomly ordered, it would be hard to compare the slices.

Embino

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Reply with quote  #6 
Whilst we are on the subject of food related data displays, perhaps I could suggest this as an appropriate use of a pie chart?  I think it gets its message across just perfectly - Stephen I await your critique...

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grasshopper

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Reply with quote  #7 
Embino - I like your pie chart!   It compares the part to the whole, so I think it should be safe.

One suggestion, you might want to add an 'Other' slice ... or, at least I've heard a lot of people say they would like "another" slice, when it comes to pie! ;)


sfew

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Reply with quote  #8 
Embino,

This is the one pie chart, apart from their occasional usefulness on geo-spatial displays, that I consider worthwhile. I feature it in my table and graph design course as such.

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Stephen Few
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