With the rare Shonen Junai Gumi/GTO-tier exception, the viewership of sequels follows a very solid rule of thumb; fewer people tend to watch the second season, and the ones who do tend to be ones who are generally in love with the franchise. But not everyone who loved season 1 of a given show will end up watching season 2. In real life, stuff like time constraints, stress, and other shows all serve as potential distractions from continuing to support a franchise. Though people who buy hard copies of a show are generally in that group of hardcore fans, they’re still human, and any number of factors could cause them to keep their cash in their wallets. If myanimelist rankings tend to overestimate the quality of a sequel, then sales might tend to underestimate its appeal.

So it’s worth asking the question; what percent of its sales does a typical show “lose” when it moves on to season 2? Since I already had a list of series that got sequels from 2005-2012 laying around from my work on the sequel probability equation, and most of those sequels have been at least partially made by now, it’s a fairly simple question (barring one wrinkle) to address.

I have to make one clerical point before I get to the results. Originally, the list of series with confirmed TV sequels was 119 series long. However, some of those sequels (chuu2koi, Stardust Crusaders, Psycho Pass, etc.) haven’t come out on BD/DVD yet, and we can’t measure their dropoff. More importantly, some of those sequels are more than direct continuations that pick off where the last season left off. Reboots like Shaft Negima and spinoffs/prequels Fate/Zero are qualitatively different enough in setting from previous seasons that counting them as direct sequels riding season 1’s coattails would be a stretch. The 11 series I classified as reboots/retools are listed in the sheet named “Reboots” on the breakdown doc.

Two other caveats. One, these series are season 1->season 2 dropoffs. I didn’t measure the dropoffs from season 2 to season 3 or later, because a very small number of shows get more than 2 seasons. Two, this sample includes “false” sequels that take place less than a year after the original aired, because what we’re looking for here is the change in presence and level of fan interest, which can change pretty significantly in 6 months’ time.

So, for the 101 series with non-reboot TV sequels that I had sales data for, the average dropoff of sales was 20%, with a standard deviation of ±31%. That means that shows experiencing a dropoff from anywhere to negligible to 50% are experiencing an “average” level of dropoff. Of the 101 series in the sample, 77 fell somewhere within this range.

So what does this mean? Well, for starters, it serves as a warning against interpreting moderate degrees of dropoff as a stinging indictment of the second season. While producers would obviously rather not have a show lose 40% of its support base, the shows that get sequels are typically the ones that can tank that amount of loss. And the phenomenon is a regular enough one that they had to have known what they’re dealing with when they decided to make the show. We can talk about shows taking >50% dropoffs as suffering exceptional loss of interest,* but any dropoff less significant than that is an average result, not a stinging indictment of everything the second season ruined.

*Looking at you, Seitokai no Ichizon Lv. 2 (89% dropoff). Although the endless eight portion of Haruhi Suzumiya (54% dropoff) is probably a more popular example, that show changed the director and went gangbusters in sucking all the energy and spirit out of an awesome, better-than-it-had-any-right-to-be comedy.