The three laws of great graphs contains Seth Godin’s guidelines for charts used in presentations:
1. One Story
2. No Bar Charts
In Seth’s Three Laws of Great Graphs, I agreed in principle, but suggested changing item 2 to “Choose Chart Types Intelligently”, because bar charts are not intrinsically worse than any other chart type.
In Bar graphs vs. Pie charts, Seth further explains his comments about bar charts:
[T]he purpose of a chart or graph is to make one point, vividly.
I think we’re in agreement on this point. Seth mentioned non-scientists, so I guess another underlying theme is “don’t make them think about this information”. I think we can agree that sometimes that’s also our intention.
Seth showed a pie chart which is used to get the audience to agree that we need to address the issue of Trolls (the following is my recreation of Seth’s chart; it’s essentially the same using Excel 2003′s inferior formatting effects):
Yes, it clearly shows the dominance of Trolls over the other creatures, as Seth points out. As long as a pie chart is used in this context (“See, Trolls make up the largest sector of our target market”), then I guess it’s pretty innocuous.
I guess it’s a matter of taste. I still prefer a bar chart to show the relative sizes of the categories:
In fact, using data from a bar chart Seth posted next to the pie, I’ve constructed a compound bar chart that readily shows that not only are Trolls a problem this year, but they were also a problem last year, and are projected to be a big problem next year, if we don’t act now.
This one will convince even the most numerically illiterate (“innumerate”?) in the audience. If you tried this with three pies, you’d only cause more confusion.
Seth finishes by saying
I can think of dozens of good uses of bar graphs… they’re not forbidden, they’re just overused and misused.
I can think of many good uses for several chart types, and no good uses for others. Charts with gratuitous 3D and formatting effects are among the most misused, abused, and overused of all chart types, and should be forbidden. Pie charts are also abused and overused, and if not forbidden, should be placed on probation. The major chart types I use (bar, line, and XY charts) are certainly abused and misused, but I wouldn’t say that well made ones are overused by any means.