Books
Great summer reading intentions? Go for books under 700 pagesGetty

Summer is here and it's time to relax on a beach with a book. But will you ever finish what you start reading, or leave it to gather dust? If it's Steven Hawking's A Brief History of Time, it might be the latter...

An American mathematician has compiled a list of abandoned books by using the highlights feature on Amazon Kindle.

Jordan Ellenberg, a professor at the University of Wisconsin-Madison, created the Hawking Index (HI) to calculate how the top highlighted passages were spread through popular books, hypothesising that when people stopped highlighting, they had likely stopped reading.

Writing for The Wall Street Journal, Dr Ellenberg admitted the method was "not remotely scientific" but was for "entertainment purposes only". Nevertheless he applied the formula to some of Amazon's bestsellers with intriguing results.

The most "unread" book came out as Capital in the Twenty-First Century by Thomas Piketty, with an HI of 2.4%.

"It came out just three months ago. But the contest isn't even close," Dr Ellenburg wrote.

At almost 700 pages long, the last of the popular Kindle highlights end on page 26, as readers seemingly abandoned their quest to find out about wealth and income inequality since the 18th century.

The most to the least-finished books (from highest to lowest HI):

The Goldfinch by Donna Tartt: 98.5%
The Pulitzer Prize-winning third novel from Donna Tartt is one of the most completed books, according to Dr Ellenburg, as all top five highlights come from the final 20 pages. Published in October 2013, the book was selected as one of the 10 Best Books of 2013 by the editors of The New York Times Book Review.

Catching Fire by Suzanne Collins: 43.4%
The 2009 science fiction novel, the second book in The Hunger Games trilogy, is another one which is read the whole way through. Dr Ellenburg noted that the line "Because sometimes things happen to people and they're not equipped to deal with them" is the most highlighted sentence in the seven-year history of Kindle, marked by a whopping 28,703 readers.

The Great Gatsby by F Scott Fitzgerald: 28.3%
Another page-turner, the 1925 novel follows a cast of characters living in the fictional town of West Egg on prosperous Long Island in 1922. With love triangles and a dystopian setting, the story is a cautionary tale about the American Dream and a portrait of the Roaring Twenties, with gripping themes of decadence, idealism, social change.

Fifty Shades of Grey by EL James: 25.9%
Although rather a different kettle of fish, the top highlights in the erotic bestseller are surprisingly clean. Dr Ellenburg stated that one of the most popular lines in the book is the slogan: "The growth and development of people is the highest calling of leadership."

Flash Boys by Michael Lewis: 21.7%
For a non-fiction book, Mr Lewis's focus on high-frequency trading in the US equity market is well-read. Published in March, the day after the book was released the FBI announced an investigation into HFT, with regards to possible frontrunning, market manipulation and insider trading.

Lean In by Sheryl Sandberg: 12.3%
According to Dr Ellenburg, the top highlight in this self-help book is not one the author penned herself, it was attributed to Alice Walker, author of the critically acclaimed The Color Purple. "The most common way people give up their power is by thinking they don't have any," is the readers' favourite.

Thinking, Fast and Slow by Daniel Kahneman: 6.8%
Although it seemed to engage readers less than Sandberg's book, The New York Times bestseller and winner of the 2012 National Academy of Sciences Best Book Award is twice as long. This means the score likely represents as much total reading as Lean In.

A Brief History of Time by Stephen Hawking: 6.6%
The popular science book was first published by Bantam Dell Publishing Group in 1988 and sold over 10 million copies in two decades, but is still one of the least-finished books, according to Dr Ellenburg's index.

Capital in the Twenty-First Century by Thomas Piketty: 2.4%
Written by French economist Thomas Piketty, the book reached number one on The New York Times bestselling hardcover non-fiction list in May 2014. Nontheless, it is Dr Ellenburg's least-finished book.