By now people are familiar with the Kindle’s “View Popular Highlights” feature, which lets you see the passages other readers have highlighted. It’s a little jarring to see at first, but it makes the reading experience social, cuing you in on the precise value that other people drew from the book and letting you contribute your point of view.

That said, it may also be inadvertently revealing the very page at which people lose interest and stop reading.  In the last couple weeks, I’ve been re-reading some favorites, underlining case studies and stats that I’ll want to find later (this feature has made my work so much easier).  After the fourth book, I noticed a pattern:   the underlines stop about a third of the way through.

Assuming that the people who highlight are the most passionate about the topic, what does the lack of underlining signal for the rest of the reading audience?  Is this a measure of where people stop reading?

I don’t know for sure, but I went through 10 books on social media and recorded the last point in each where underlines appear.  Then I noted the percent point in the book for that spot. (Finally, some value in Amazon’s decision to use percentages instead of page numbers!)

Here are the books, ranked by the percentage point at which the last highlight appears.  The average? 34.8%

1. Six Pixels of Separation: 68%

2. The Wisdom of Crowds: 58%

3. Here Comes Everybody: 45%

4. Socialnomics: 40%

5. Social Media 101: 39%

6. The Long Tail: 35%

7. Groundswell: 26%

8. The New Community Rules: 15%

9. Trust Agents: 14%

10. The Cluetrain Manifesto (10th Anniversary Edition): 8%

If these numbers really do mark where the covers close for good, it’s a shame.  Right away I can tell you that five (the ones I’ve read) are totally worth reading to the end.  Colleagues have strongly endorsed the others.  Cluetrain’s 8% is especially shocking as it’s easily one of the most brilliant pieces of economic and political writing in the last few decades. (FYI only the 10th anniversary edition is available on Kindle, but it’s been out for a year, so it’s not exactly fresh off the press.)

Is this wrong?  I hope so and invite you to poke holes in this thinking.  Heck, maybe the average nonfiction books looses its readers at the 25% point and these social media gurus should do a victory dance.

If you have a Kindle and want to add the highlight percent point you’re seeing for other social media books, please add them in the comments.  I picked these simply because they’re the ones I knew, and I heard of them mostly from blog posts and friends.  And if you’d like to make a real gift to the community, put in a lesson learned or critical stat YOU got from these books beyond the percent point at which most people stopped reading.  Maybe it’ll convince people to go back and see what they’ve missed.