What graphs should you use in your presentations?
Marketing uber-guru Seth Godin recently posted an interesting set of guidelines (and a follow-up coda) on his website. As is customary for our culture, Seth’s rules were three:
1. One Story
2. No Bar Charts
His rules quickly were a lightning rod for controversy, so let’s separate the wheat from the chaff:
1. One Story Seth says (and has said before) that a graph should avoid nuance and be easily understandable in two-seconds and should make only one main point. But Seth is giving his advice in the context of making a memorable, high impact presentation, where (in Seth’s words) you need to make a “point in two seconds for people who are too lazy to read the forty words underneath.”
Other types of contexts require different types of graphs. Reports can handle more complex graphs (but executive summaries should probably be simpler), exploratory analyses can go even more complex, and data-visualization as art need not even be readable!
But let’s take a second look at that quote. By calling your audience “too lazy to read the forty words underneath” Seth is assuming that the audience doesn’t care. This echoes what he says in his follow up post
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.
Again, this only matters when your audience is not invested in your topic. For topics and presentations where there is much more intrinsic interest among your audience, you can get more nuanced. But there is no reason a nuanced chart cant also have a simple message, as the Junkcharts blog points out. Or, as Jon Peltier puts it, by removing nuance, you are insulting your audience, telling them that “They can’t handle the truth!”
2. No Bar Charts. Seth has made the point before that a bar chart can obscure the truth, and muddle your story. Instead, he suggests using a pie chart. A confession: I hate pie charts (as do others who make graphs for a living), but they do have a time and a place for simple graphic displays, especially since audiences are familiar with them and expecting them. But don’t scorn the useful bar chart! Yes, they can be misused, but so can any other type of graph, and (as pointed out by Stephen Few) pie charts are actually perceptually inferior to bar charts even for presenting simple data. The one point I do agree with is that bar charts should not usually be used to display time series results (often line graphs are better for that) (Seth defended his no bar charts decision in his follow up post–to stop this from turning into Moby Dick, we’ll address that with our own follow up post). The issue here is really using a chart, and choosing the data, that best illustrates your story for your audience.
3. Motion. Seth really dropped the ball here. For someone that understands the distraction caused by PowerPoint’s dubious dissolves and annoying sound clips (pdf), his suggestion of creating two slides with graphs set up to show changes is just as cheap and distracting a trick. Stephen Few has a much better suggestion (although even this can be improved), to show the change by making parallel bar graphs. Here the story is “Trolls were a problem, but Gremlins are now.”
If trolls and gremlins were the only categories on the graph, then Seth’s suggestion would work great. And if the biggest problems are all you care about, then that is fine. But if you have this data and your story is different, you need a different graph and a different presentation style than Seth suggests.
The BOTTOM LINE
Design your charts (and all your materials) with your story and your audience in mind.
And as for this non-controversy, we’re really all on the same team here–we all want clear, interesting presentations. Seth wants to accomplish that by limiting what people do with graphs; those who he (dismissively) calls data purists want to educate people to do more with their graphs so they make the right choices. Seth’s plan works for the novice. But when the training wheels are ready to come off, I think it’s better if presenters know how to make the best choices for the needs of their story.