Guidelines for designing information charts often state that the presentation should reduce ‘chart junk’–visual embellishments that are not essential to understanding the data. . . . we conducted an experiment that compared embellished charts with plain ones, and measured both interpretation accuracy and long-term recall. We found that people’s accuracy in describing the embellished charts was no worse than for plain charts, and that their recall after a two-to-three-week gap was significantly better.
As the above-linked blogger puts it, “chartjunk is more useful than plain graphs. . . . Tufte is not going to like this.”
I can’t speak for Ed Tufte, but I’m not gonna take this claim about chartjunk lying down.
I have two points to make which I hope can stop the above-linked study from being slashdotted and taken as truth.
1. The non-chart-junk graphs in the paper are not so good. Figure 1 is a time series of dollars that is unhelpfully presented as a bar chart and which is either unadjusted for inflation or, if adjusted, is not indicated as such. Figure 2a is a lineplot that whose y-axis should go down to 0, but doesn’t. Both graphs also use the nonstandard strategy of labeling the y-axis on the right rather than the left. Figure 2b is an impossible-to-read pie chart with one of the wedges popping out of the circle. Regular readers of this blog will know what I think of that. Figures 2c and 2d are blurry and have no axis labels. Figure 2d is particularly bad because it’s a time-series graph in which time is presented on the y-axis; it also has the problem with inflation adjustment noted earlier. Figures 4-9, presenting their own findings, are not particularly easy to read either.
Chartjunk aside, it’s hard to make good graphs, so I can’t really blame Bateman et al. for their performance here. They’re doing about as well as might be expected in routine psychology research. And maybe they’re right that crappy chartjunk graphs are better than crappy non-chartjunk graphs. But I don’t think it’s appropriate to generalize to the claim that chartjunk graphs are better than good graphs.
2. This brings me to my second point, which is that a huge, huge drawback of chartjunk is that it limits the amount of information you can display in a graph. If all you want is to display a sequence of 5 numbers, then, sure, go for the chartjunk, I don’t really care. But why limit yourself to only displaying 5 numbers? Consider the graphs in Red State, Blue State (or in our other research publications, or on this blog). Sure, you can do pretty instead of plain (see this discussion with examples), but here the graphics design is used to enhance the points made in the graph, not as a distraction.