a measure of how many people actually read the book

invented by mathematician Jordan Ellenberg writing for the Wall Street Journal

”mock mathematical measure on how far people will, on average, read through a book before giving up”

It is calculated based on the most popular highlights marked by Kindle users. If there is a large concentration of quotes in the beginning but lesser as it progresses, the book ranks low on the index. It attempts to measure how spread out the highlights are.

Named after Stephen Hawking’s book A Brief History of Time which is a popular book that people start but don’t finish. The HI of the book was 6.6%.