Merian who runs the Boreal Perspectives blog posts on a Sankey diagram that visualizes academic career paths.

This was originally shown in a 2010 Royal Society policy report entitled “The Scientific Century: securing our future prosperity”. Merian raises concerns about the quality of the diagram. She goes: “So what’s so bad about the chart? Some obvious issues:

  • It is unclear what goes in on the left and to a lesser degree what is covered by the end points. The report indicates in a footnote that the term “science” is used “as shorthand for disciplines in the natural sciences, technology, engineering and mathematics,” but the three documents used for input categorise the fields in different ways, and there is no indication which fields exactly would have been selected.
  • Line thickness is not proportional to percentage weight. The 26.5% and 30% streams have the same thickness, and the 17% stream is much less than half the thickness of either. The 3.5% stream is more than half the thickness of the 17% stream.
  • Why does “Permanent Research Staff” not end in an arrow? And why does the arrow from “Permanent Research Staff” to “Careers Outside Science” bend backwards (to suggest it is a step back in one’s career, that is, an implicit value judgement?) and then not even merge with the output stream?
  • Does it really mean to suggest that no one goes from “Early Career Research” (that is, a post-doc) to “Career Outside Science” (or to industry research)? In my experience, watching post-docs, that is quite a common choice for post-docs precisely because non-academic jobs may be offering better pay and conditions, or because they don’t have a choice at that stage.”

She then presents a remake of the above diagram made using the Sankey plugin for d3.js

Indeed, the distribution diagram without the arrow heads seems to be better suited. The overall appearance is much more calm.

Merian, however, concludes “no graph would have been more useful”.

In early November I was pointed to an image on the Innovation Strategy Canada website [the website itself is not accessible any more] by a reader of this blog. Peter asked whether I know of any Sankey diagrams for financial flows, like they are shown in the one below.

The diagram visualizes the sources of R&D funding, and the institutions receiveing this funds. Data is from Statistics Canada for 2006 and shown in Mio (supposedly) Canadian Dollars.

While there are only four different arrow widths to show the financial flows, the interesting thing is that the sums of funds from each source and received by each beneficiary are shown as cylinders (database symbols, tanks, …).

I quickly did several versions of the diagram, but was not too happy with the results. The flow quantities are OK, but as it turns out, it is difficult to see the volume of the cylinder, supposedly to scale with the sums. This information is redundant anyway, since the width of the joined arrows at their base or at their head is exactly the sum that is supposedly to be shown by the cylinder volume.

Here is one version of my Sankey diagram for R&D funding in Canada for 2006 based on the original image. I decided to make the boxes in different sizes (the problem remains the same: can one immediately grasp the area of each box).

Your comments are welcomed. Is there a better way to display the sums?