The waterfall of book sequels + + + +

Some sequels are a waterfall from grace. Others barely drop. Which book series have the highest drop-off rates?

Psychedelic mushrooms were a great inspiration for Frank Herbert when he wrote Dune, the seminal 896 page sci-fi book, in 1965. This comes as no suprise when you read the book. A mind-enhancing drug called melange, or spice, is central to the story. It also contains an arid and treacherous desert planet, a well of esoteric technology, as well as giant sandworms that devour all in their path. Who among sci-fi and fantasy fans could resist such a promise?

Upon reading the first few pages, however, complexity unravels. Great political intrigue, a big cast of characters, and philosophical themes are woven into the story. The language is more difficult. It might take many pages for the reader even to get into the story. It did for me. In fact it took me years of picking it up and putting it down before I finished it. Like that Herzogian penguin that wanders off alone in Antartica, a question arise: but why?

First the numbers should be explained.

Finding precise number for book sales is difficult. The numbers that do exist are largely estimates. In addition, they do not account for usage. Like multiple people reading the same book or being affected by “tsundoku”.

To examine reading habits, I therefore base my analysis on registered reviews from Goodreads. Goodreads users as a whole are very consistent on reporting their reading habits. Still, self-reported numbers are not entirely accurate statistics. There are margins of error and cross-checking sources are vital. The StoryGraph, a similar platform to Goodreads, also provide similar data. They show that the trends are consistent across platforms.

And among fantasy and sci-fi, there are two series that stand out. In each their own direction.

The result is striking. Dune seems to lose many readers after book one. Only a small fraction that read the first book, also read the last. The fall is especially big after the first book.

This is a big contrast to the relatively new book series “A Court of Thorns and Roses” that retains its readership with flying colors. Half of those who read the first book, also read the last book. That is a very high retention rate.

Other numbers tells a different story. For the “Harry Potter” series, readers are very likely to finish the whole series if they have read through book number two. Many book series don’t have a dramatic fall after the second book, which could indicate that readers who are invested in certain series are more likely to finish them.

Still, what causes this fall off? One could speculate that it is tied to how good you think the book is. If you didn’t like a certain book in the series, you should be less inclined to read the next. That should be common book math.

In Dune’s case, there seem to be a correlation. The first book is favored, but the sequles, while well received, follows a rating pattern similar to the drop-off pattern. Foundation provides a different story. While the drop-off pattern is similar to Dune, the ratings are actually pretty stable for the series. This shows that a correlation between ratings and drop-off rate is highly unlikely.

Maybe difficulty plays a role. Dune is often described as difficult to read. The language can seem a bit dry and old-fashioned to modern readers. The story is complex and can be hard to follow.

The StoryGrpah provides such numbers. Users can self-repport how difficult they found a book. Maybe repported difficulty shines a light on the drop-off pattern.

The overall retention trend declines with difficulty. Readers fall off more often on difficult book series. The data is limited however, and there are clear outliers.

Dune is an extreme outlier in difficulty. It also is the measured series with the lowest retention rate. Foundation and A Court of Thorns and Roses both have similar difficulty, yet wildly different retention rates. This shows that difficulty isn’t the only factor at play. Easy reads aren’t necessarily being finished more often.

It is difficult to know what causes some series to be read while others are not. Difficulty is likely to have an impact. Ratings not so much. Regardless, maybe it’s time to pick up that sequel that have been gathering dust on the shelf?