I love Buffy the Vampire Slayer. It’s a show filled with some of the most fully-realized characters on TV and it features a diverse cast that is all too uncommon these days.

Fans have argued over which seasons or episodes are the best for the better part of the last two decades. In my analysis, I sought to answer the question of which season, by virtue of its high ratings and consistency, was really the best.

I used IMDB data (https://datasets.imdbws.com/) and downloaded the datasets available in February 6, 2018. Then I used R to combine the tables and filter out the data so I only had info related to BTVS. I also removed the pilot (S1 Ep0).

Before analyzing episode ratings, we have to make sure our data is appropriate. The average number of votes per episode reaches a high of 1992 for Season 1 episodes and a low of 1262 votes per episode for Season 7. Sample sizes that big are appropriate for our analysis here.

Figure 1. Density of individual episode ratings

The data is skewed to the right, with most of the episode ratings hovering around 8.25.

I created a boxplot by grouping the episodes by season, then looking at the average user rating per episode. The result:

Figure 2. Boxplots of average user ratings. Black line corresponds with median in black. The line running across represents the mean rating of all episodes

For those unfamiliar with a boxplot, the box holds the first and third quartile of the data. Meaning that the top 25% and bottom 25% of the data is found outside the box, while 50% of the data is contained within it. A smaller box (and shorter whiskers) correspond with smaller deviation within episodes of the season. Hence, a smaller box implies more consistent ratings between episodes and a more consistent season overall.

The smallest box and only one that is fully above the mean rating is the third season. Its whiskers don’t extend as far up as some other seasons, indicating that season 3 doesn’t have the “highest highs” of the series. A full rundown of the seasonal averages are as follows:

If we were to stop right here, we would put the Buffy seasons as: 3>5>2>7>6>4>1. The means might not tell the whole story, however. For additional information, we can also look at the coefficient of variation. CV, as it is also known, is the ratio of the standard deviation over the mean. It is a measure of spread, and a smaller CV corresponds with more consistency.

Season 3 is the most consistent of the bunch, followed closely by Season 7. Season 5 (holding our #2 spot above) is in the middle of the pack in terms of CV, while Season 2, our #3, is the least consistent season. Season 4 is the other set of episodes with high deviation. Unsurprising, considering it’s the same season that brought us both “Hush” (9.7) and “Beer Bad”.

Another possible metric is the frequency with which a season has “good” episodes. “Good” being a subjective term, I looked at the distribution of the ratings and found that the third quartile rating is 8.7. This means that 25% of the episodes in the series have a rating higher than 8.7. These top-tier episodes are distributed as such:

Season 3 is king, tied with Season 2 for highest amount of top-quartile episodes. For an even more granular look at season highs, look at the number of episodes per season with more than a 9.0 rating:

Season 7 lost the most from the added scrutiny. It is important to note that I set the cutoff at 9.0. IMDB only stores ratings up to one decimal point, so setting the cutoff point at 9.0 instead of 8.9 resulted in quite a few episodes disappearing from the table.

Given how seasons look so differently based on how you look at the data, I thought it would be more appropriate to put seasons into tiers.

Tier 1: Season 3

There’s no doubt about it. The season that gave us “The Zeppo”, “Doppelgangland”, and both “Graduation Day”s is the height of Buffy the Vampire Slayer. It might not feature the very best episodes, but it is the most consistently good, high-quality Buffy that you can watch.

Tier 2: Season 2, Season 5

Season 2 and Season 5 are opposites, in a way. Buffy’s first foray into a full, 22-episode schedule had the most high-quality (>9 rating) episodes in the series. Season 5, meanwhile, was like a lesser version of Season 3; consistently good but missing stellar episodes.

Tier 3: Season 6, Season 7

The tail end of the Buffy series was not without its detractors, but no one can deny that it had its moments. After all, Season 6 gave us “Once More, With Feeling”, the pinnacle of BTVS as voted on by IMDB users. Season 6 had a higher number of episodes rated 9 or above, but its average episode score falls just shy of Season 7's.

Tier 4: Season 4

Season 4 might be one of television’s most uneven seasons (I’ll be sure to look into that for a future post). The season’s outrageous highs are overshadowed by its hum-drum central narrative and the “so bad it’s good” Beer Bad.

Tier 5: Season 1

Buffy’s freshman outing was a mixed bag. At times it felt like the season was trying to be a new X Files. Other times, it was just plain silly. Remember when Willow fell in love with a demon-controlled computer?