Can You Trust Championship Odds?
Fangraphs World Series Odds 2021
At the end of MLB’s regular season, FanGraphs predicted that the Atlanta Braves had a 9.6% chance of winning the World Series.
33 days later, Atlanta hosted a World Series parade for the first time since 1995.
Despite the Braves’ low odds, it doesn’t mean you can’t trust Fangraphs. In fact, if you were to look at their championship odds since they began in 2014, the Braves’ win wouldn’t be a complete shock.
(Note: this article focuses on championship odds at the beginning of the playoffs. If you want to know more about FanGraphs’ playoff odds, you should read their article on how well their playoff odds work here.)
Here is a table displaying championship odds for each playoff seed, averaged over the prior seven playoffs, their actual championship percentage, and the differential between the two:
Prior to 2021, the odds of the team with the highest odds were favored to win it all just under a quarter of the time. For every four World Series, Fangraphs projected the top team would win .96 times (not even once).
In actuality, the highest-odds team had only won once in the seven seasons with Fangraphs championship odds (2020 Dodgers). While this meant this spot was underachieving, it’s not as bad as it looks.
Because of small sample size, even a win this year by the highest-odds team would mean the spot was overperforming by over 2%.
Additionally, the second and third-highest odds teams have only overachieved by a win apiece.
The most severe underachievement, then, isn’t from the first spot, but the collective fifth through ninth spots.
Despite having combined average odds of over 30% from 2014-2020 (an expected 2.1 championships in the seven years), fifth through ninth-highest odds teams had combined for zero championships.
Before the 2021 playoffs began, FanGraphs believed the Los Angeles Dodgers had the highest odds of winning the World Series.
Unlike previous seasons, FanGraphs’ championship odds were more uncertain than ever.
Here’s what each team’s championship odds looked like coming into the 2021 playoffs:
At 16.6%, the 2021 Dodgers had the lowest odds of a team from 2014-2021 that were favored to win the World Series by 2.9%. Its odds were more than 7% worse than the average favorite from the previous seven seasons.
The Astros, the projected runner-up, had a 15.2% chance of winning the World Series. This was also lower than average odds for its spot, with odds 1% lower than the average second-best odds team.
The White Sox and Brewers, who had the next highest odds, fell roughly within the average of their respective rankings. The worst-odds Cardinals had odds that were 1% lower than what was average.
This meant that there was much more opportunity for parity for the fifth through ninth-best projected teams. The combined championship odds of the Braves, Giants, Red Sox, Yankees, and Rays was 41%, over 10% higher than what we would expect in an average year. And these were just the odds of one of these five teams winning the World Series, much less appearing in one.
While this doesn’t mean a World Series win was guaranteed for any of these teams, they were viewed as having a much better chance by FanGraphs than in previous seasons.
When the Braves walked away with the Commissioner’s Trophy, it became the first team with the fifth-highest odds in the FanGraphs championship odds era to win it all. While FanGraphs predicts less than one championship every ten years, fifth-highest odds teams are only overperforming by 3.75% (8.75% expected versus 12.5% actual).
The Astros’ loss actually helped the projection model avoid serious overperformance for the second-ranked team. Had the Astros won, second-ranked teams would be over-performing by 21%!
Of course, this doesn’t mean FanGraphs odds are perfect. No projection model is. FanGraphs bases odds on how they expect players to perform within the playing time they are projected to receive. It’s easy to critique the odds when the 88-win Braves have higher odds than the 107-win Giants and 100-win Rays. But just because a team has the third or fifth or tenth-best championship odds (looking at you, 2014 Giants) according to FanGraphs, it doesn’t mean the projections believe it’s impossible for your team to win, just that it’s less likely.
It also means that when one of these teams wins, it isn’t proof that the models and projections are bad, it simply means that something incredible happened.
We’ll need a sample size much larger than eight to know just how accurate FanGraphs’ championship odds are. However, the past eight World Series should make you feel comfortable with their projection model. The current distribution of championships compared to the average odds are a good sign that it’s closer to accurate than not.