A common criticism of charts is that they are filled with chart junk, and that removing the extraneous elements would make the chart better and stronger. That argument works for analytical charts, but not for charts that are used for presentation. The way memory works suggests that chart junk is actually very useful to not only get a point across, but make sure the reader remembers it.
Recap: The Chartjunk Paper
Bateman et al. looked into the effects of what is commonly referred to as chart junk: embellishments, graphical elements, etc. that are not strictly part of the chart, and that can be removed without reducing the amount of information the chart carries. The study found that the embellished charts were more memorable, in particular after a longer time period (two weeks) than the plain charts. Also, they found that embellishments did not interfere with subjects’ understanding of the data.
Criticism. Lots of It.
There has been considerable criticism of the paper, and much of it is probably valid: the sample size was small, the criteria left too much room for interpretation and/or experimenter influence, etc. Also, the charts used were very simple, with unstated assumptions about the data.
My point here is not to argue whether the criticism is justified, but that it misses the point. The bigger point we should get from the paper is that we need to be clearer about what we want the user to do with a chart.
We don’t remember isolated facts about the world. Confronted with information, we immediately try to make connections, and those connections help us remember facts. If you’re presented with some fact that has little or no connections with the other things you know about, you won’t remember it. A fact that fits well into the existing network of your knowledge will be retained much better.
We also embellish and elaborate information to remember it. That may be done subconsciously, or it may be an elaborate mnemonic device we use to make sure we retain a fact. Sometimes these techniques tie facts to certain locations, or we make up a little rhyme or poem around them. The interesting thing is that not only do these embellishments help us retain the information, in the long term we also remember the facts rather than the mnemonic devices.
The User and Her Task
There is a lot of talk about tasks in visualization, but most of the time, the task is analytical: analyze network traffic, find fraudulent transactions, etc. But what if the task is to remember a fact? Don’t we need to address that case differently than the usual analysis task?
The examples the Bateman study used were all taken from newspaper and magazine graphs that were not meant to be used for analysis. Rather, they presented information to the user, either as self-contained little information packages, or as illustrations accompanying articles.
The user task in these cases was not to analyze large amounts of streaming data or look for hidden patterns, but rather to take in a small chunk of information. The goal was not a new insight, but the communication of a fact.
What is so easily dismissed as chart junk therefore is actually a good idea in this case. In fact, the task requires something other than a boring, generic chart that looks like the next one. Unique embellishments help the user get the point, make connections, and remember the information. That is exactly what these charts were made to do, and the study showed that they did their job.
An interesting experiment would be to not only test people’s retention after two weeks, but after two months or a year. I bet the group that saw the embellished chart still had a memory of them, while the plain, boring charts are probably lost among all the other ones a person has seen in the meantime.
Thinking Outside the Analytical/Perceptual Box
For all its flaws, I am convinced that the Bateman et al. paper will prove to be highly influential in the longer run. But if it doesn’t, I think we’re in trouble.
Visualization has seen some research on perception, and that work has made its way into many techniques and rules we use today. We are still incredibly weak when it comes to higher-level cognitive processes like memory and learning, though. These processes are equally, if not more, important, in particular when it comes to presentation and communication of data. Data-to-ink ratio is a useful concept, but we need to start understanding when it should be used, and when other considerations are more important.