Millions may have held their suspicions, but last month the Canadian e-reader company Kobo confirmed it: Most people who buy The Goldfinch don't actually finish it. According to the company's data, less than half of Canadian and British Kobo readers in 2014 made it to the end of Donna Tartt's behemoth novel, one of the best-selling of the year.

How did Kobo know this? Like every e-reader and reading-app maker today, the company, a subsidiary of the Japanese e-commerce titan Rakuten, has access to a comprehensive suite of data about the reading behavior of its users. In a white paper titled "Publishing in the Era of Big Data" and released this fall, the company announced that "with the onset of digital reading ... it is now possible to know how a customer engages with the book itself — what books were left unopened, which were read to the very last word and how quickly." In other words, if you read books digitally, the people who serve you those books more than likely know just what kind of reader you are, and just how little effort you made with Infinite Jest.

The paper was a rare peek into the nascent world of reader engagement analytics, which have been a staple of web publishing but which the big legacy book publishers have been slow to embrace. It was fascinating, not just for the insights it offered into reading behavior (Did you know the industry standard finish rate for mystery books is 62%? Now you do!) but because the enormous corporations — Amazon and Apple — that know the most about how you read are ferociously silent about that knowledge. Both Apple and Amazon declined to comment for this piece.

The findings precipitated a now-predictable response from the loftier perches of the publishing world. In a leery New York Review of Books blog post, titled "They're Watching What You Read," the novelist Francine Prose wrote, "...writers (and their editors) could soon be facing meetings in which the marketing department informs them that 82 percent of readers lost interest in their memoir on page 272. And if they want to be published in the future, whatever happens on that page should never be repeated."

(This kind of rhetoric is nothing new. In a 2012 Wall Street Journal article bearing the similarly alarming headline "Your E-Book Is Reading You," Jonathan Galassi, the president and publisher of Farrar, Straus & Giroux, declared, "We're not going to shorten 'War and Peace' because someone didn't finish it.")

It's true that engagement analytics pose a highly abstract threat to a certain idealized kind of furrowed-brow, human-and-their-word-processor, Great Novel writing and reading, as well as to those people whose livelihoods and self-images are invested in that ideal. ("Excuse me, Mr. Joyce, you're losing a lot of Kindle Fire readers here in this third section. Maybe tighten it up a smidge?") But it's also true that most books released by the declining publishing industry are hardly War and Peace, that so far these numbers have played almost no role in editing and acquisitions in the publishing industry, that they have far greater implications for marketers than they do for writers and editors, and that the companies making the most significant use of engagement analytics aren't traditional publishing houses, but startups.

According to Claudia Ballard, a book agent with William Morris Endeavor, there is still only one salient number when it comes to the books that get picked up.

"The truth of the matter is people have been picking up books and not finishing them for a long time," Ballard told BuzzFeed News. "At the end of the day, a unit sold is still a unit sold."

Editors at several major publishing houses, who spoke to BuzzFeed News on background, agreed. While these editors were aware that engagement analytics exist, and were aware that their sales departments had some form of access to them (though it's still unclear both how much reader engagement data Apple and Amazon collect, and how much of it they share with publishers, including those, in Amazon's case, of their own imprint), they all said these numbers had nothing to do with acquisitions or editing.

Could that change? Well, for engagement to rival sales purely as a measure of commercial importance, and as a factor in acquisitions and editing, books would have to be monetized in a much different way: namely, in-book ads. These kinds of experimental ads have been tried, and, according to independent publishing entrepreneur Richard Nash, they've mostly failed.

"As best as anyone can tell, it has to do with the fact that the average book is read by not that many people," Nash told BuzzFeed News. "Advertising is a volume business and there's not that much to sell when you're talking about 18,000 eyeballs."

That's not to say that editors don't want to see them, and not for purely financial reasons. To use Prose's example, if everyone is stopping on page 272, well, maybe there's an editorial problem on page 272!

If engagement analytics hold actual actionable advice for big publishers today, though, it probably has more to do with figuring out which books to promote and how to promote them, rather than how to edit them or which ones to acquire. In a section called "Identifying the next Dan Brown," the Kobo paper points specifically to the case of so-called "midlist" writers (those who sell well, or garner critical acclaim, but are not major money makers) with high engagement rates as inadequately marketed.

A major factor in the failure to complete books is, of course, lack of time. Safari, a platform for professional education books (it's wholly owned by O'Reilly Media, which publishes coding tutorials), aggregates reading data to point users to relevant sections in separate books. It's easy to imagine this model being applied to mainstream books, especially in non-narrative and nonfiction titles. (Say, a collection of highly read jambalaya recipes pulled from 20 different cookbooks.)

Last year, the publishing giant Macmillan announced Next Big Book, a collaboration with the analytics company Next Big Sound — which tracks sales, publicity, social media activity, and traffic stats (among other things) — to determine which of these factors is most influential in driving a book's popularity. (It doesn't yet include engagement metrics in its analytics, though Next Big Sound CEO Alexander White told BuzzFeed News that it may eventually.) And Macmillan has started to distribute some of this data to writers. So it's not impossible to imagine a point at which writers commonly have access to engagement data.

Would this, as Prose fears, change the way writers write? Of course, most authors have never seen engagement statistics for their work. But Eli Horowitz, formerly the managing editor of McSweeney's and now a founder of the mobile storytelling startup Ying, Horowitz and Quinn, had access to reader data for The Silent History, a serialized digital novel that he co-wrote. Yet after the project was complete, Horowitz and his co-creators actually spent very little time with the data for pretty understandable reasons: lack of time, and fatigue.

"We didn't do it because we had other stuff to do and the book was written," Horowitz told BuzzFeed News. Asked if the data might prove useful for future projects, Horowitz said no, because "I don't want to write that novel again."

Indeed, using any data — even sales data — to futurecast in publishing has always been a dangerous prospect because of years-long lead times and the personal investment involved in writing a book. Trends change, and writers move on. "It's not a quick post the author is going to jot off," Ballard, the book agent, said. "They have to live with a book for years or a decade. To live in that space for that long you have to be mentally prepared to have all sorts of feelings about it, and you have to really want to write it, not simply because you think people will want to read it. That place of passion is always where good books come from."

So don't expect Prose's page 272 scenario anytime in the near future, if at all. Of engagement-based editing, Nash said, "We haven't seen anything yet and I'm skeptical that we'll end up with much. Not even Netflix, which is deeply interested in analytics, was telling Kevin Spacey how to act [in House of Cards]."