Everyone knows that the number of pages per book in the famous series by J.K. Rowlings increased over time, but was this increase steady? Was it consistent? The answer seems to be no.

Looking at this graph, is is probably more accurate to say that the early books were a certain length, around 400 pages or less, and the later books (4 through 7) were longer, around 700 pages. This may seem like a trivial observation, and it probably is. But it is important to understand the basic pattern of page length over time in this series before we explore the more important and deeper meanings of it all.

By the way, and this is a small digression, I had asked a while back about which Harry Potter movie disks would be the best ones to get in order to have a complete collection. At the time, I ended up buying this one:

Harry Potter Years 1-6 Giftset [Blu-ray]

It seems to have all the movie bits and some extra material as well. Then, more recently, I picked up the DVD/Blue Ray of the final movie, number 7b:

The reason this is interesting is that I never did see that movie in theaters, because it came out a few days after Julia left the country for an extended trip, and in sympathy for her pain of missing this movie’s opening, I refused to watch it until she returned. Meanwhile, the DVD/Blue Ray of the final movie, Harry Potter and the Deathly Hallows: Part 2, came out just a few days before Julia’s return. So we watched it yesterday.

Anyway, back to our analyses…

People seem to wonder, and comment, quite a bit about the relationship between these books and these movies. It might be useful to explore the basic pattern of this relationship. We might ask if the longer books yield longer movies, for instance. Does the number of pages in a Harry Potter book predict the number of minutes in the corresponding Harry Potter movie?

It does not take fancy statistics to examine this. The answer, simply, is no.

Ignore the one dot that is up and to the right. Looking at only the first seven movies, as book length goes up, movie length does not. The dot all by itself in the upper right is the combined length of the last two movies on the number of pages of the final book. (The seventh book in the series was made into two movies.) I could have split the book into two parts and regressed each of those parts on the appropriate movie length but since we can see that there is no relationship, that would not have been worth the work.

Finally, for completeness, we have this:

This just shows the variation across the series of seven books in movie lengths, with the runtime for the seventh book being a combination of the last two movies. The scatter plot above is, essentially, this bar chart and the first bar chart combined.

I have a few observations to offer, some of which were suggested to me by Julia.

To the extent that book length is higher in the later part of the series but the movie lengths mostly stay the same, we see a decrease in the degree to which the movies faithfully and completely represent the book. As Julia puts it, the first movie basically used the first book as a script, but this approach does not hold through the series.

The length of the seventh book as a movie … which was so long that it was divided into two parts … may have been appropriate for a number of reasons, but it is not predicted by the pattern seen earlier.

As the series went on, the movie makers seemed to regularly include numerous “cute” scenes showing things that were not central to the main plot but still made the books and movies interesting, such as Nevillle blowing himself up every time he tried something in class, or various interactions among the main characters that were not related directly to either the book’s plot or the overarching themes of the series. However, the last two movies have very little of this, and the last movie virtually none. In fact, if you look at deleted scenes from the final movie (7b) there is one such scene … when Ron and Hermione are running away from the big snake and she tells him to not say anything one might say while being chased by a big snake, but might regret saying later.

The fact, assuming that it is true, that the movies don’t simply script out the books, increasingly over the series, together with the fact that the books don’t get steadily longer (but rather, stay about the same length for a while then switch to a different length for a while) tells us something about either the books or the way the movies are made. I suspect that the contents of the books simply became thicker, even when the books themselves didn’t, and using the book as a straight forward template for a movie based on the book became increasingly difficult.

The simple idea of the books getting longer and the movies getting harder to fit into the usual time slot does not explain what we’ve been seeing. More likely, the nature of the books has changed in important ways across the series, as literary works, as well as the approach take to represent them on the silver screen.

The books: