I often refer people toMorris Rosenthal’s Graph of Sales Rank vs. Sales for Amazon. It’s the best I’ve found, and an admirable resource.
A commenter on Estimating Sales, Part III was having difficulty with the logarithmic nature of that graph. So, rather than answer the question in a very loooong comment, I’m adding it as a post.
Logarithmic graphs are used when a curve is complicated and hard to handle on a regular graph. We use them to straighten out the line, or remove one level of complexity from our attempt to get the formula for the line.
That’s the why of them, but the question was how do we use them. Our needs are simpler than a scientist or engineer’s.
To use the Amazon Sales Rank Graph, you need to know that each order of magnitude (1, 10, 100, and so on) starts with a large distance between one number and the next, and the lines get closer and closer together as you approach the next one.
The lines between 10 and 100 are 20, 30, 40, 50, 60, and so on, even though they’re never numbered. You can interpolate between those lines, using logs yourself, but we don’t want to do that.
Why don’t we? Because we’re estimating sales based upon historical data. The numbers aren’t very accurate in the first place. Our average sales rank isn’t. The implications of that rank aren’t (across years and seasons, and the vagaries of Amazon’s programmers).
So what do you do? Suppose that your book’s comparables are all in the range of 50,000 sales rank. Count forward from the line for 10,000 or back from the line for 100,000 (or both). Run down that line, and find where it crosses the red curve. As I write this, that point is also where curve crosses the horizontal line for 20 books per week. It’s actually not quite at the corner, but we’re not going to interpolate for further accuracy on the graph.
In fact, we’re not even going to multiply by 52 weeks per year to get annual sales. Just use 50. It’s close enough. (And better to be under than over!)
So, that’s how you duck the complexities of the log scales. If you are interested in more information about logarithmic graphs, I recommend the Wikipedia article on the subject.
I’m not really sure that I made myself clear above. If you have a question I didn’t clarify, please let me know in the comments, and I’ll take another try at it.
The Profitable Publisher — A new E-Book Series
January 12th, 2010Hello all,
I have finally (!!) released the first ebook in my new series. Yes, the series name is The Profitable Publisher. This first entry is subtitled: Making the Right Decisions. It’s short (maybe 40 pages, if you printed it out), so it shouldn’t give your brain indigestion.
I’d like to think that it should help any publisher make more money from all of your books. If you are moved to purchase it (from Amazon, or elsewhere as it comes out in other markets), do please let me know what you think?
Tags: decision analysis, ebook, financial analysis
Posted in For Authors, General Comments, Publishing Answers | 4 Comments »