In its annual summary of ISBNs registered for self-published works, Bowker reported that nearly 730,000 were issued in 2015, up from 153,000 in 2010. The numbers cover ISBNs issued for both print and digital formats.
The ISBN is a useful way to monitor sales across the supply chain, but works published on a single platform can forgo the identifier and rely on platforms such as Amazon to report performance. Because the creators of many self-published works do not apply for ISBNs, the number of new works published each year is believed to be greater than Bowker is able to report.
When the number of self-published works was lower, this gap in the data was something the publishing community could live with. As the number of self-published titles has grown, however, there’s a sense that the share of sales for these works is also growing.
The debate about the true size of the self-published market continues. Traditional publishers and advocates for independent works have each tried to position the market as more or less tilting their way. To date, we’ve not seen much of a discussion about why knowing the size of the book market matters.
Here’s one reason it matters: mobile content discovery and consumption.