Hanging things on your charts
Jul 20, 2021
The Financial Times published the following chart that shows the rollout of vaccines in the U.K.
(I can't find the online link to the article. The article is titled "AstraZeneca and Oxford face setbacks and success as battle enters next phase", May 29/30 2021.)
This chart form is known as a "streamgraph", and it is a stacked area chart in disguise.
The same trick can be applied to a column chart. See the "hanging" column chart below:
The two charts show exactly the same data. The left one roots the columns at the bottom. The right one aligns the middle of the columns.
I have rarely found these hanging charts useful. The realignment makes it harder to compare the sizes of the different column segments. On the normal stacked column chart, the yellow segments are the easiest to compare because they share the same base level. Even this is taken away from the reader on the right side.
Note also that the hanging version does not admit a vertical axis.
The same comments apply to the streamgraph.
Nevertheless, I was surprised that the FT chart shown above actually works. The main message I learned was that initially U.K. primarily rolled out AstraZeneca and, to a lesser extent, Pfizer, shots while later, they introduced other vaccines, including Johnson & Johnson, Novavax, CureVac, Moderna, and "Other".
I can also see that the supply of AstraZeneca has not changed much through the entire time window. Pfizer has grown to roughly the same scale as AstraZeneca. Moderna remains a small fraction of total shots.
I can even roughly see that the total number of vaccinations has grown about six times from start to finish.
That's quite a lot for one chart, so job well done!
There is one problem with the FT chart. It should have labelled end of May as "today". Half the chart is history, and the other half is the future.
For those following Covid-19 news, the FT chart is informative in a different way.
There is a misleading statement going around blaming the U.K.'s recent surge in cases on the Astrazeneca vaccine, claiming that the U.K. mostly uses AZ. This chart shows that from the start, about a third of the shots administered in the U.K. are Pfizer, and Pfizer's share has been growing over time.
U.K. compared to some countries mostly using mRNA vaccines
U.K. is almost back to the winter peak. That's because the U.K. is serious about counting cases. Look at the state of testing in these countries:
What's clear about the U.S. case count is that it is kept low by cutting the number of tests by two-thirds, thus, our data now is once again severely biased towards severe cases.
We can do a back-of-the-envelope calculation. The drop in testing may directly lead to a proportional drop in reported cases, thus removing 500 (asymptomatic, or mild) cases per million from the case count. The case count goes below 250 per million so the additional 200 or so reduction is due to other reasons such as vaccinations.