Amazon sales rankings

Every now and then, I have a look at my books on the Amazon site, to check if there are any new reviews from readers.  Whenever I look at the sales rankings, I am amazed -- and cannot see any rhyme or reason in what those rankings are.  For example, a book recently published (like "The Strange Affair...") may have a sales rank higher than "On Angel Mountain", which has now sold well over 20,000 copies and which still sells steadily on Amazon.

It's all to do with the strange Amazon algorithm, which can move a book up and down by 100,000 places or more just on the basis that two copies of the book have (or have not) been sold through Amazon during the course of a week.  It's a mad world...... and the best thing, I suppose, is not to worry about it!

This is what Morris Rosenthal says on his interesting web site: 
http://www.fonerbooks.com/surfing.htm

"The new system, while it requires the author/publisher to keep checking over a period of time to establish an average rank, doesn't appear to include any funky constants. A spike in the rank over a couple days is usually due to a special book promotion by the author or publisher. It takes a long term book marketing strategy to actual raise the sales (and average rank) over a long period of time. Unfortunately, establishing an average rank has gotten much harder as the number of books that actually sell a few copies a week has grown. If you check the rank every day and it varies by less than a factor of two (ie, between 5,000 and 10,000 or between 600 and 1,200 or between 100,000 and 200,000) then you can take a week's worth of rankings, divide by 7, and get a reasonable average. But if the rank bounces around much more than that, you'll have to check daily for a few weeks and discard a couple outlying points on the low end and high end or the result could skew badly. For those authors don't want to visit Amazon all the time, you can use salesrankexpress.com to check all of your books at once and also see other important info. Amazon books are selling so many copies these days that a title with an average rank around 40,000 that goes two days without selling a copy may see it's rank drop by more than 150,000 points.The more books Amazon sales, the more violent the rank movements outside the top couple tens of thousands of books that consistently sell multiple copies a day.

Under the new system, the sales ranks of top books don't dip because some title out of left field suddenly sells three copies in an hour, that won't get them past 20,000, and they'll start sliding back towards left field the next hour. Also, as you move outside the top 100,000 titles that sell a copy every day, ranks can bounce around a little without a sale, depending on a weak historical time constant. Under the old system, books in the top 10K were daily reset to a relaxation rank, even with no sales. The sales rank decay rate depends where a book falls in the continuum; strong sellers decay slowly, mediocre sellers decay quickly, and weak sellers decay relatively slowly. All books are now re-ranked every hour."

Morris says he used to include a table giving some equivalent sales numbers for some distinct ranks, but he later dropped it.  He continues: "Nobody outside of Amazon knows EXACTLY how many copies of a given title are sold in a given time period, and since ranks are relative to each other, it's a constantly moving target. The idea behind my reverse-engineering the ranking system was always to give rough idea of how a title was selling, not an exact number. So, don't read an average rank of 10,000 to mean you sold exactly 60 books that week, or a rank of 100,000 to mean you sold ten and a half copies - Amazon doesn't sell half copies."

And what do rankings actually mean?  He gives this useful rule of thumb:  "Read an average rank of 1,000 to mean you have a seriously successful title, an average rank of 10,000 to mean your doing pretty good for a book that's no bestseller, an average rank of 100,000 to mean it's not going to contribute significantly to your income, and an average rank of 1,000,000 to mean you need to take a break from checking sales ranks."

Thanks to Morris for consent to cite the above text.   Check out his site -- there is a lot of very useful material on it.