(reblogged from Nicholas C. Rossis)
- “Why did my sales rank go down when I sold more books this week?”
- “Why did my sales rank go up when I didn’t sell anything?!”
- “How did the sales rank of this book leapfrog over mine when I’ve sold ten times as many books?”
For example, why did Honest Fibs hit #40,215 in its first week of launch, after only a couple of dozen sales?
Amazon won’t disclose their proprietary algorithms, but thanks to some clever analysis by indie authors, that formula has been reverse engineered. And once you understand that formula, the quirks of sales rank make much more sense, and you can use them to your advantage.
The basics of Amazon’s sales rank algorithm are surprisingly simple:
- Each sale or download of a product counts as one point toward a hypothetical “rank score”.
- Depending on the day, the preceding day’s score decreases by half, and is added to today’s points.
- For each category on Amazon, books are ranked based on their current scores.
There are some caveats, though. For example, as author Carolyn McCray points out, #2 would have you think that a book selling copies worth 128 “points” on Day-1, then never sells another copy, would see the following ranking:
- Day-1 128 points
- Day-2 64 points
- Day-3 32 points
- Day-4 16 points
- Day-5 8 points
- Day-6 4 points
- Day-7 2 points
- Day-8 1 point
In fact, there are multiple drop-off points, the first being the 24-hour window. After 24 hours your sales numbers are cut in half, but this does not happen daily. As a matter of fact, you are stable for several key periods: a week, a month, 3 months, 6 months, 12 month and 18-months.
That is why most people price too high for too long after a promotion and then suddenly, after a month of steady sales, fall from the sky in flames.
The most severe of these drops is the 30 day one. If you don’t bolster sales and convince the algorithm that you can still sell, you will fall off a rankings and sales cliff after a month.
Other factors include the following:
Sales rank is relative to other books
A book does not exist in a vacuum. As your book rises in sales rank, it will displace other books. As other books rise through the ranks, your book may be pushed downwards.
This counterintuitive feature of the algorithm is responsible for more confusion than any other.
The more recent the sale, the more weight it has
Because the formula weights sales by recency, the effect of a sales spike quickly fades. The algorithm favors steady sales over a dramatic surge.
Consider the two books below (Figure 1). Book A experiences slow, constant growth for the first two weeks. Book B offers a promotion which results in an explosion of sales, but those sales quickly settle back to normal levels once the promotion ends.
At the end of the second week, Book A holds a higher sales rank — and has better visibility — even though Book B sold over three times as many copies.
In the long run, steady, organic growth outperforms sudden bursts of activity.
That is why publishing success is a marathon, not a sprint, so authors should be focused on long-term success.