Another amazon calculation (and perhaps an interesting one)

I was chatting with my friend, Steve, yesterday on the way to Inception, and was started talking about the long tail of sales. In particular, he made the contention that far more books are sold in the long tail (i.e bad ranks) cumulatively than up above. I started to think about it, and by gum if he isn’t right!

I’ve been thinking about amazon ranks for some time now, and my latest estimate is:

daily sales = (average rank / 130,000)-0.7

This seems to hold at least from rank=1,000 (and possibly much higher) up to a few million. In fact, I wouldn’t trust this up to much higher ranks than about 2 million, because at that point you’re looking at less than 1 amazon sale/week.

Does this hold up to the top? Probably not, but if it does, the #1 bestseller is selling about 3,800/day. Actually, I can believe that with Harry Potter-esque exceptions (on opening day), this is fairly reasonable. Stay #1 for a year, and we’re talking well over a million sales on amazon alone.

But it’s a simple matter of calculus to figure out the relations of things. For example. Approximately 25 times as many books are sold from book #101-2,000,000 as are sold from book #1-100.

Interesting… I wonder how well this actually holds up.


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