What makes a good anime?

What makes a good anime? While taste is subjective, there tends to be some sort of consensus on quality. For example, most people think Frieren is a good anime. Using user ratings and genre tags, I measure which genres correlate with higher anime quality. I estimate an item-level quality score for each anime using a matrix-factorization model, then investigate how that score varies with genre and with genre combinations.

Estimating anime quality from ratings

I obtained the rating data from Anime Recommendation Database 2020. I then estimate a simple matrix factorization model:

$ r_{u,i} = \mu + b_u + b_i + p_u^\top q_i + \epsilon_{u,i}$

where:

I fit the model with regularization, then standardize the $b_i$ values to have a mean of 0 and a standard deviation of 1. All regression coefficients reported below are expressed in these standard deviation units.

Which genres are common?

An anime can belong to multiple genres. Broad genres (e.g., Comedy, Action, Fantasy) contain many anime, while narrow genres (e.g., Samurai, Cars, Vampires) contain few anime.

Counts of anime per genre

Estimating the effect of genres

I regress anime quality on binary genre indicators yielding the following estimates:

Regression coefficients for genres with 95% error bars

While a few genres (mostly those that appear infrequently) have wide error bars, we’re able to achieve relatively precise estimates for most of the genres. The strongest positive associations with anime quality are Thriller, Mystery, and Drama. Genres connected to sexual content or romance (e.g., Yaoi, Ecchi, Shounen Ai) tend to have negative or near-zero associations. Curiously, the aforementioned pattern does not apply to the Romance genre, which has a solidly positive association. The multiple regression model achieves an $R^2$ of 0.25, and the regression’s predicted quality correlates with empirical quality at $r = 0.50$.

Estimating the effect of genre combinations

We might expect there to be interactions between genres. Restricting ourselves to two-way interactions, there are 946 possible interactions, but only 771 of them actually occur, and only 179 of them are present in at least 100 anime. Because testing many interactions inflates false positives, I adjust p-values with the Benjamini-Hochberg procedure and list the interactions with adjusted p-values less than 0.01, which are as follows:

Interaction Estimate (SD units)
Slice_of_Life:Supernatural 0.59
Comedy:Parody 0.59
Comedy:Harem 0.43
Action:Horror 0.41
Ecchi:Sci_Fi 0.41
Comedy:Demons 0.39
Ecchi:Harem 0.38
Fantasy:Slice_of_Life 0.37
Action:Supernatural 0.30
Comedy:Drama 0.21
Sci_Fi:Shounen -0.30
Ecchi:Romance -0.31
Drama:Mystery -0.35

A Sanity Check: The Top Anime

Looking at the highest-quality anime (excluding sequels) gives us a sense of how credible the genre-quality associations are. The genre most strongly associated with quality, Thriller, is overrepresented, appearing twice in the Top 10. The runner-ups, Mystery and Drama, are also overrepresented. At the other end, none of the top anime belong to sexually themed genres. We can also find positively associated interactions such as Slice of Life × Supernatural and Comedy × Parody represented among the top anime.

Anime Genres
Fullmetal Alchemist:Brotherhood Action, Adventure, Comedy, Drama, Fantasy, Magic, Military, Shounen
Legend of the Galactic Heroes Drama, Military, Sci-Fi, Space
Steins;Gate Sci-Fi, Thriller
Gintama Action, Comedy, Historical, Parody, Samurai, Sci-Fi, Shounen
Clannad: After Story Comedy, Drama, Romance, Slice of Life, Supernatural
Code Geass:Lelouch of the Rebellion R2 Action, Drama, Mecha, Military, Sci-Fi, Super Power
Your Name. Drama, Romance, School, Supernatural
A Silent Voice Drama, School, Shounen
Monster Drama, Horror, Mystery, Police, Psychological, Seinen, Thriller
Gintama Season 5 Action, Comedy, Historical, Parody, Samurai, Sci-Fi, Shounen
Mushi-Shi Adventure, Fantasy, Historical, Mystery, Seinen, Slice of Life, Supernatural

Caveats

The estimated effects aren’t causal. We don’t know why certain genres are associated with higher (or lower) anime quality. It may be that some genres are inherently more appealing, or it could be that competent anime creators focus more on certain genres over others. Or possibly neither of these explanations fit and the truth is something else.

Appendix

Genre Descriptions

MyAnimeList has a page describing the different genres, which, in addition to being incomplete, is also inaccurate. For example, it claims that “Slice of Life and Comedy are incompatible by definition”. However in the dataset, there are 1034 anime that belong to both genres. As I am not well-versed in anime, I turn to the all-knowing chatbots to briefly describe each genre.