Using Mean, Mode and Median to Evaluate Also-Boughts

Self-pubbed authors are always debating ebook pricing strategies. Former math editor that I am, it occurred to me that you could look at data gleaned from your book’s also-boughts to see what they tell you about the customers who have bought your books.

The also-boughts (or “alsobots”) are typically located under your book’s product description on Amazon. They look like this. (Click to enlarge.)

In this case the author (not me) has about 17 pages of books that were bought along with his. If you go through each of the titles and write down the book prices, you get a nice collection of data on purchasing patterns.

A refresher is probably necessary here.

The price (or prices) that appears most frequently is/are known as the mode

The average of all the prices—add them all up and divide by the number of individual prices—is the mean.

The number that appears in the middle of all these prices when you rank them from lowest to highest is the median.

One of my books—a nonfiction collection of my science articles—has only 5 pages of also-boughts. When I worked my way through the calculations, here’s what I found:

* I had 20 data points in all.

* The mean (average) price was $5.0035, or $5.00.

* The median (right-in-the-middle) price was $2.99.

* The mode (most frequent) price was $.99.

(You don’t have do these calculations by hand, by the way. You can use calculators like this one, this one or this one.)

This gives us some food for thought. You can use the results to ask yourself some questions:

* Am I pricing too low? (If both the mean and median are higher than your book’s price, you might consider adjusting.)

* Am I pricing too high? (Both mean and median are lower than your book’s price.)

* Am I living in cheapskate city? (Your mean and median are consistently lower than those of ebooks by comparable authors. The mode and even the median for all your titles is always $.99.)

Traditionally published books by name authors tend to display also-boughts that are solidly in the mainstream price range: $9.99 to $12.99.

Are the customers who’ve bought these books ignorant of the ocean of better-priced self-published books out there? Are they consciously avoiding them? Is there too much competition to be listed as an also-bought for a book by a Patterson, a Lee Child or even a Malcolm Gladwell that the algorithm favors higher-priced books over lower-priced ones? Does the evidence support the suggestion that there’s a self-pubbed pricing ghetto?

Or are there other reasons?


This kind of data is interesting but problematic, for the following reasons.

* Book prices are dynamic. The price you’re seeing in also-boughts when you do your calculations may not be what customers originally paid.

* Inclusion as an also-bought is highly selective. You’ve sold a thousand of a certain title. Great. But you don’t see 1,000 also-boughts or even 500. You’re getting skewed data to begin with.

* Those who’ve designed software similar to the kind used by Amazon say systems can be inaccurate when reflecting customer buys or making recommendations. Think how often Netflix, Twitter, or Tumblr recommend films or follows you’d never spring for in a million years.)


Math is fun, but maddening when you don’t have all the facts. Mean, mode and median can be an interesting guide, but not the only one. My gut tells me to price my books somewhere in the range between $2.99 and $4.99, and this analysis seems to support my gut. (My median was $2.99 and my mean is $5.00.)

But this is what drives me nuts. Part of me can’t help wondering if I’m not caught in a self-fulfilling loop. Six of my also-bought data points are for ebooks priced $8.99 or higher. If customers were willing to spring for those books, why wouldn’t they spring for mine at that price? Sane me answers, “Because your name isn’t Oliver Sacks, Malcolm Gladwell, or Mary Roach, dumbass.”

So: If you’re picking prices with your gut, you might welcome the chance to put some calculations behind your decision. Just understand that the analysis may not be any more accurate than your gut. And if you’re like me, your brain will still give you doubts.