Bloomberg Businessweek has a special edition about vaccines, and I found this chart on the print edition:
The chart's got a lot of white space. Its structure is a series of simple "treemaps," one for each type of vaccine. Though simple, such a chart burns a few brain cells.
Here, I've extracted the largest block, which corresponds to vaccines that work with the virus's RNA/DNA. I applied a self-sufficiency test, removing the data from the boxes.
What proportion of these projects have moved from pre-clinical to Phase 1? To answer this question, we have to understand the relative areas of boxes, since that's how the data are encoded. How many yellow boxes can fit into the gray box?
It's not intuitive. We'd need a ruler to do this task properly.
Then, we learn that the gray box is exactly 8 times the size of the yellow box (72 projects are pre-clinical while 9 are in Phase I). We can cram eight yellows into the gray box. Imagine doing that, and it's pretty clear the visual elements fail to convey the meaning of the data.
Self-sufficiency is the idea that a data graphic should not rely on printed data to convey its meaning; the visual elements of a data graphic should bear much of the burden. Otherwise, use a data table. To test for self-sufficiency, cover up the printed data and see if the chart still works.
A key decision for the designer is the relative importance of (a) the number of projects reaching Phase III, versus (b) the number of projects utilizing specific vaccine strategies.
This next chart emphasizes the clinical phases:
Contrast this with the version shown in the online edition of Bloomberg (link), which emphasizes the vaccine strategies.
If any reader can figure out the logic of the ordering of the vaccine strategies, please leave a comment below.