# Some fun with math

Bridget McKenna posted to Passive Voice about how kids are enthusiastically adopting e-books. McKenna writes that the study "plays hell with the 30% e-reading cap so many people have been predicting lately."

The thing is, their own data plays hell with that particular prediction!

Let's pretend that the surveys of established publishers bear any actual relation to the e-book market. (They don't.) This data suggests that e-books constitute 25% of sales, and is increasing at a rate of 34% a year.

So, assuming that rate of growth stays constant:

In 2013, e-books will make up 34% of book sales.

In 2014, e-books will make up 45% of book sales.

In 2015, e-books will make up 60% of book sales.

In 2016, e-books will make up 81% of book sales.

In 2017, e-books will make up 107% of book sales, which is impossible.

You see why I laugh when people describe a 34% rate of growth as not truly impressive.

But the rate of growth is slowing! they scream.

OF COURSE that rate of growth is going to slow, at least as a percentage of the overall market. It has to! You can't actually control 107% of a market--it's like eating 107% of a pie! (Although, if e-books actually cause the overall market to grow the way paperbacks did, we may see the value of e-book sales in 2017 top the overall value of all book sales in 2012. Which would be very cool.)

Anyway, let's halve the rate of growth, making it 17%.

In 2013, e-books will make up 29% of book sales.

In 2014, e-books will make up 34% of book sales.

In 2015, e-books will make up 40% of book sales.

In 2016, e-books will make up 47% of book sales.

In 2017, e-books will make up 55% of book sales.

So, at half the current rate of growth, within five years more than half of all book sales will be e-books.

What the people predicting a 30% cap on e-books are predicting is basically a zeroing out of e-book growth--not a reduction in that rate of growth, but a complete halt. And they are expecting that zeroing-out to happen, you know, today. Because if the rate of growth stays anywhere near where it is now for just a couple of years, e-books will be outselling every other format--paperbacks, hardcovers, you name it. And that's in dollar value.

I actually do think we might see a zeroing out of e-book growth in the next few years among traditional publishers, but that's because I think it's quite possible that that particular group is going to be largely forced out of e-books. In that case, e-books will be left to the indie writers, who are much harder to survey.

What's that 30% cap? It's wishful thinking. It's people pretending they know the future when they don't. It's inconsistent with existing data from publishers of fiction. And it's extremely unlikely.