Here is how it works: the company gives free e-books to a group of readers, often before publication. Rather than asking readers to write a review, it tells them to click on a link embedded in the e-book that will upload all the information that the device has recorded. The information shows Jellybooks when people read and for how long, how far they get in a book and how quickly they read, among other details. It resembles how Amazon and Apple, by looking at data stored in e-reading devices and apps, can see how often books are opened and how far into a book readers get.

Jellybooks has run tests on nearly 200 books for seven publishers, one major American publisher, three British publishers and three German houses. Most of the publishers did not want to be identified, to avoid alarming their authors. The company typically gathers reading data from groups of 200 to 600 readers.

Mr. Rhomberg recently gave a workshop at Digital Book World, a publishing conference in New York, and some of his findings confirmed the worst fears of publishers and authors.

On average, fewer than half of the books tested were finished by a majority of readers. Most readers typically give up on a book in the early chapters. Women tend to quit after 50 to 100 pages, men after 30 to 50. Only 5 percent of the books Jellybooks tested were completed by more than 75 percent of readers. Sixty percent of books fell into a range where 25 percent to 50 percent of test readers finished them. Business books have surprisingly low completion rates.

How Will Publishers Use the Data?

For the most part, the publishers who are working with Jellybooks are not using the data to radically reshape books to make them more enticing, though they might do that eventually. But some are using the findings to shape their marketing plans. For example, one European publisher reduced its marketing budget for a book it had paid a lot of money to acquire after learning that 90 percent of readers gave up after only five chapters. A German publisher decided to increase advertising and marketing on a debut crime novel after data showed that nearly 70 percent of readers finished it.