Good news for fans of long, immersive literature: According to a recent survey by Vervesearch on behalf of interactive publisher Flipsnack, bestselling books are getting longer. Vervesearch chose 2515 books from The New York Times bestseller and notable books lists and Google’s annual survey of most-discussed books, and found that, on average, page length has increased by 25 percent over the last 15 years, growing from around 320 pages in 1999 to 400 in 2014.

It’s a fascinating finding, though its implications are unclear. Some believe the shift from print copies to digital e-readers has encouraged readers to pick up longer books. James Finlayson from Vervesearch told The Guardian that he believes seeing a large book in a bookshop can be intimidating to casual readers, whereas “on Amazon the size of a book is just a footnote that you don’t really pay all that much attention to.”

But according to The Guardian, some of the most popular e-book genres, such as romance and crime, produce the shortest books. In contrast to Finlayson's theory, Granta editor Max Porter believes that the popularity of long books has its roots in a cultural, rather than technological, shift. As he explained it to The Guardian, “The novel has come into its own novel-ness. There so many demands on our attention, so many competing forms, that these novels have decided to relish being big and long, to demand that you sit in a chair, turn off your phone and devote some time to them.”

Further research is likely needed to pinpoint why books are getting longer. For now, readers can form their own theories—or just jump into one of the long, excellent novels on the current New York Times bestsellers list.

[h/t: The Guardian]