A few days back, Matthew Beckler added the Kindle edition to his sales rank tracker for How to Teach Physics to Your Dog. Given my well-known love for playing with graphs of data, it was inevitable that I would plot both of these in a variety of ways.

So, what do we learn from this? Well, we learn that people in the Albany. NY area don’t own Kindles:

OK, maybe that’s not obvious to everybody…

When you look at that graph, the blue line is the Amazon sales rank of the physical book edition, while the red line is the Amazon sales rank of the Kindle edition. The two track each other pretty well for a while, but diverge dramatically after about 48 hours, with the physical book sales rank shooting into the triple digits, while the Kindle sales rank stayed around 3,500. So, what happened at 48 hours?

The only significant development that I’m aware of that took place around then (which was about 1pm ET Sunday) is that both the Albany Times Union and the Schenectady Gazette ran articles about the book (the Times Union had a piece about the book written for them by a freelance writer, the Gazette went with the AP review, plus a notice of this weekend’s signing). Nothing else happened around that time that I know of.

So, this tells us that notices in the local papers were enough to drive up the sales rank of the physical book, but not the Kindle edition. So, people in the Albany area don’t own Kindles. Or, to be more precise, people in the Albany area who read print newspapers (neither the Gazette nor the Times Union put the book on their web sites) don’t own Kindles.

Amazing what you can learn from looking at graphs.

The other obvious thing that you can do with these data is to look at what relationship, if any, exists between the book sales rank and the Kindle sales rank. The easiest way to get at this is to plot one on the vertical axis and the other on the horizontal axis:

I’ve divided the data into two sets for this graph. The purple points at the first 48 hours of the data set, and the green are the last 48 hours. For the first 48 hours, they track each other pretty well– a straight line drawn through the purple points would come close to most of them, and has a slope close to 1 (1.27, to be precise). It’s not perfect, but it’s plenty good enough for social science.

The green points are way off that line, for the most part, but there’s a big clump of them over in the upper left, that would fit reasonably well to a line with a slope of a bit less than 3 (making a rough cut of that group gives a slope of 2.93). Those points are the stretch from Sunday afternoon through Monday night, when the physical book rank was at its highest point.

There’s also a sort of a tail connecting the Sunday-Monday group, as the book rank drifts back up to more or less where it was before the dramatic spike. At the time of this writing, the book rank is back up to 2500, which is about where it’s been since the AP review ran.

So that’s this week’s thrilling installment of Playing With Graphs…