Wednesday, 1 August 2012

How pie charts are bad for your analytical health

The main reason when we visualize information in charts or graphs is to make it easier to interpret and compare information within, however, using Pie Charts have proven the opposite. Why? As Steve Fenton puts it


1. Pie charts made it difficult to compare individual values.

Nasty Euro Election Pie Chart

As this example taken from the 2009 BBC News European Election Results suggests, even though it is reasonably clear that the Conservative Party has the biggest chunk of the vote, it is definitely hard to see the difference between the next three parties, UKIP, Labour and the Liberal Democrats. It is also quite hard to tell the difference between the next two parties, Green and BNP. As the purpose of the chart is to tell the differences between each party, using a pie chart proves to difficult in achieving this.


Fantastic Euro Election Column Chart


Now if we compare to the bar chart above, it is so much easier to see the difference between the items.


2. The size of a pie chart wouldn't make any difference.

Shocking Tiny Pie
Awful Large Pie

From the same data as above, resizing a pie chart would not reveal anymore data, and the space taken to resize just to make it clear would only be a waste.


Excellent Tiny Column Chart
Stunning Huge Column Chart


Compared to the bar charts above, the smaller chart is already showing a clear difference between the columns, but when enlarged you'd get a more clearer picture of the differences.


3. Displaying combined values.


Disasterous UK Election Pie Chart

From the 2009 BBC News European Election Results above, if we wanted to see how would the Conservative party fare when say the Labour party were to join forces with the Liberal Democrats, its very hard to tell using the pie chart above.

Brilliant UK Election Column Chart
If we observe the same using our bar chart, we can clearly see that the combined party could have an edge over the Conservative party.

Aside to the 3 arguments above, there are more details showing how pie charts are not the best choice. and 3D pie charts? Let the chart below explain everything :)


Suck on that, Conway.

You can follow the rest of the story on pie charts here and also here

All images are taken directly from the source blogs to the credit of the authors.

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