Alberto Cairo speaks on his blog (in spanish) about the use of circles instead of bars that are spreading all around the world, inffluenced by The New York Times.
He uses this image to demonstrate that people understand better when we measure just changing one dimension (height or width) and not both. And he's right. And we, in Púbico, must recognize the 'mea culpa'. He doesn't say that circles are bad for graphics, we thinks they¡re right when we wnat the reader not the know the exact cypher, but a global vision.
I absolutely agree with Alberto, although I think there's one more reason for using circles: sometimes, with brs, the differences are so extreme tat there are not any possible way to place it on page. This times, circles are easier to place, showing the real difference, and without 'cutting' the bar. I prefer a difference that is not so clear at first sight that one that is 'false'. Anyway, I think is an advice more than needed.
There's another reason to use circles, and I won't recognize I've said this later... Writers and editors like color circles rather than neutral bars. As we stare to paes with puppies and babies. It's not a powerful reason to include this kind of graphics, and we never do it for this reason, but we must recognize that that 'exists'.
PS. TAlking about Alberto Cairo, he release his new infographics book in Spain in September. The bok is calledInfografía 2.0. Visualización interactiva de información en prensa (Inforgraphics 2.0, Interactive visualization of information on newspapers). This is not the book we've already talked about, Visual Journalism, but a good one to keep waiting. Just a problem: would be released just in spanish.