Mathematician Jordan Ellenberg ran some numbers for the Wall Street Journal to determine which of Amazon's most popular e-books people start but never finish. The classic example, apparently, is Stephen Hawking's A Brief History of Time – but the astrophysicist's rarely-read bestseller was far from this summer's least-read book.

Photo Credit: andreannecg via flickr | CC BY 2.0

Ellenberg describes how he formulated the "Hawking Index," what he admits is an imperfect metric of unread-ness:

Amazon's "Popular Highlights" feature provides one quick and dirty measure. Every book's Kindle page lists the five passages most highlighted by readers. If every reader is getting to the end, those highlights could be scattered throughout the length of the book. If nobody has made it past the introduction, the popular highlights will be clustered at the beginning.

Thus, the Hawking Index (HI): Take the page numbers of a book's five top highlights, average them, and divide by the number of pages in the whole book. The higher the number, the more of the book we're guessing most people are likely to have read.

Bestsellers Lean In, by tech executive Sheryl Sandberg; Thinking Fast and Slow, by Nobel Prize–winning economist and psychologist Daniel Kahneman; and Hawking's Brief History of Time all fared poorly, scoring 12.3%, 6.8%, and 6.6%, respectively. But the most unread book of all, by a wide margin, was French economist Thomas Picketty's bestselling Capital in the Twenty-First Century, which came in at 2.2%.


See which bestsellers ranked highest on the Hawking Index over at the WSJ.

Complement with io9 commenters' collection of under-read SF and fantasy titles and our list of SF classics we all claim to have read (but really haven't) . One wonders how these titles would score with Ellenberg's metric.