Wall Street Journal says that the scale of layoffs in the tech industry recently is worse than those caused by the pandemic lockdown. Here is the chart:
It's the dreaded bubble chart, complete with overlapping circles. Each bubble represents the total number of employees laid off in the U.S. in a given month.
The above isn't really the chart you find in the Journal. I have removed the two data labels from the chart. Look at the highlighted months of April 2020 and November 2022. Can you guess how much larger is the number of laid-off employees in November 2022 relative to April 2020?
If you guessed it's 100% - that the larger bubble is twice the size of the smaller one, then you're much better than I at reading bubble charts. Here is the published chart with the data labels:
I like to run this exercise - removing data labels - in order to reveal whether the graphical elements on the page are sufficient to convey the underlying data. Bubbles are typically not great at this. (This is what I call the self-sufficiency test.)
Another problem with bubble charts is that the sizes of the bubbles are arbitrary. This allows the designer to convey different messages with the same data.
Take a look at these two bubble charts:
The first one has huge bubbles, and lots of overlapping while the second one is roughly the same as the WSJ chart (I pulled a different dataset so the numbers may not be exactly the same).
Both charts are made from exactly the same data! In the second chart, the smallest bubbles are made very small while in the first chart, the smallest bubbles are still quite large.
Think twice before you make a bubble chart.