I’m a big fan of Junk Charts, in this blog post you can read about Junk Charts’ test to judge the worthiness of data graphics, called “self-sufficiency”:
– Can the graphical elements stand on their own feet?
– If one removes the numbers from the graphic, can one still understand the key messages?
Graphical elements such as bars, lines, dots and pie slices encode data into their lengths, widths, heights, sizes, angles and so on. Oftentimes, the actual numbers are printed beside these elements. The numbers may serve one of two purposes: sometimes, to satisfy those readers who would want to know the precise numbers, not just rough visual estimates; sometimes, to cover up flaws in the design because the graphical elements cannot be interpreted without printing the numbers. The “self-sufficiency” test detects this last instance when the graphic designer has failed. In these situations, the data charts are superfluous; the graphical elements did nothing more than regurgitate the underlying tables of numbers.
In a way, this was what I tested out in my experiment a week ago, when I removed explanations and labels from visualizations in order to see if people still would understand them.