Bar graphs vs. Pie charts

Compare!

The bar graph is read left to right and seems to imply something about the declining relevance of Billygoats (even though close inspection shows that we expect high growth in billygoats next year). There's data here, but no information.

The pie chart contains far less data, but the point is obvious: Trolls are where we should focus our energy.

That's why you use it. It makes an obvious point and leaves no real room for discussion. I think discussions are great, but that's not why you are doing a presentation.

I stepped on the toes of many data presentation purists yesterday, so let me reiterate my point to make it crystal clear: In a presentation to non-scientists (or to bored scientists), the purpose of a chart or graph is to make one point, vividly. Tell a story and move on. If you can't be both vivid and truthful, it doesn't belong in your presentation. (I can think of dozens of good uses of bar graphs... they're not forbidden, they're just overused and misused).