Wednesday, March 28, 2007

What's wrong with pie charts?

Recently, I tried to shows the statistics of 6 major Official Direct Assistance (ODA) donor countries. My thinking was like this:

  1. No table! Make graphs.
  2. What do others commonly do? (pie charts!!)

In that very moment, I can picture that Andy shouts, "No!" What's wrong with pie charts? Here are what some experts would say.


  • Dot plots are an excellent alternative to pie charts because they show data position along a common scale rather than rely on pie chart angles.
  • Dot plots can show more information (2 dimension, 3 dimension)
  • Just for kick, here is the pie chart that came in my mind in the very beginning.

Then I tried to do a dot chart, which is no better.

The data points convey 3 different informations.

  1. The relative position shows average(ODA/world ODA).
  2. The size of the circles shows a country's ODA/GDP.
  3. The numbers attached to the data points show actually amount of ODS in US dollars.
  4. The country names in the y-axis indicate the country names of the data points, sorted by a country's ODA/GDP.

This is definitely a junk chart. What's wrong?

  • Redundant informations! 3 actually does what 1 has already done. 4 does what 2 has already done in terms of showing a country's ODA/GDP.
  • The use of position for dots was distorted because of a nominal y-axis, multiple informations.
  • The x-scaling is too small, too detailed!
  • etc.....

After talking to Andy, Jennffer and Masanao, here is the revised one:


  • (x,y) position is more intuitively situated.
  • The circle sizes still mean ODA/GDP.
  • x-axis now has wider scaling (less details) and goes to 0 (Andy,"0 is meaningful here!").
  • ODA is the x-lab is still a problem. Normally, we don't use unconventional abbreviations in charts. It just doesn't communicate if readers don't know what they mean.

So here is what the caption of this figure:

Figure: Six major Official Direct Assistance (ODA) donor countries. The size of the data points indicates a countries ODA as a proportion to its GDP. The US gives the most ODA in the world in terms of the sheer amount. But it is only 1.4 percents of its GDP. Netherlands gives almost 9 percents of its GDP.

No comments: