Tuesday, February 17, 2009

More on bad graphs

Ok, following on my very acid mood this week and after I read Nathan's from Flowing Data latest post on JP Morgan's Market Cap, which I had already seen and criticized back in January (only not on this blog), I decided to bring that little demon back and speak my mind once again.

First, let's take a glance at the graph:

The basics: Blue circles mean the market value pre-crisis and green circles mean the market value as of late January '09, both in the realm of billions of dollars.
The goal: show how hard everyone took it and given the scenario, how well JP Morgan managed not to lose as much value.
The error: trying to map 1-D values in 2-D objects without much attention to it.

So what's the big deal? The big deal is that when you use circles to map numbers, you HAVE TO remember that they are 2-D objects and as such, they have areas, which the cerebral cortex cars much more that ratio or diameter. What this means is that your brain cares much more about that area than about how tall that ellipse might be.

So how should the circles look like? Well, Rena Corda showed the world a revised version of it, here it is:

Can you see the difference? Ok, ok, maybe you don't find it that huge, but it is noticeable and as such, should be taken into account. We all know that statistics can be shown in many forms to make viewers/users agree more or less with the presenter's point of view and I personally think that this is a good thing, but there is a limit as to how much that can be used and JP Morgan's graph borders unethical information usage.
Let me know what you think...

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