Matt H., who authored the previous post, and Charles G. both pointed to a great example of how people like readers here can make a difference. A bad chart got made over!
The Financial Times published a chart from a JP Morgan report, using ... you guessed it ... bubbles to illustrate the deep plunge in market capitalization of many banks.
Some readers at the blog were none too happy with the choice of bubble charts. Among other things, the designer made the common mistake of plotting proportional diameters rather than proportional areas. This is clear from looking at JP Morgan's bubble.
This chart exposes the weakness of bubble charts well. Look at the top row of bubbles. Most of them look so similar it is impossible to know, without spending much time studying the circles, which bank was hurt more.
In fact, neither the bubble nor the bar chart works well for this case. What we need is the Case-Schiller style asset-bubble life cycle chart. In order to interpret these changes in market caps, we need to know how big was the bubble, and then how steep was the consequent decline. Take a look at our discussion of real estate bubble charts here.
Reference: "Bank capitalization chart of the day", Felix Salmon at Portfolio.com and "Bank picture du jour", FT Alphaville, Jan 21 2008.