With the so-called “hard” trade deadline approaching fast for MLB Teams, (now in a matter of hours!), we decided to once again fire up our servers and use our Bayesian model to predict each team’s end of season record, and consequently their shot of making the playoffs.
This season eliminated August waiver trades, a past opportunity to grab a player once a team’s stance has been made clearer. The most famous waiver trade perhaps was Justin Verlander moving from Detroit to Houston for the Astros’ historic World Series run in 2017. July 31 now represents a true, hard trade deadline for the first time in Major League Baseball history. If teams miss the opportunity to add to their clubs via trade by that date, there is no backup plan.
As of July 29, 19 teams are either in possession of, or 5 games behind, a playoff spot. However, only 10 teams can make the gauntlet that is the MLB postseason.
American League Playoff Picture
National League Playoff Picture
If you need a refresher on our Bayesian methodology, feel free to check out our NBA coverage 2018-2019 preseason playoff predictions, or our look back at the 2017-2018 NBA season. For a more in-depth analysis, check out our 2017 MLB Bayesian predictions. Since it has been a while though, here is a quick refresher.
At the beginning of the season, we gather win total predictions from a variety of sources, including casinos, ESPN, and other sports websites. We then average, or take the median, all of these predictions together to generate an expected win total for each team. By a phenomenon called Wisdom of the Crowds, this win total is usually more predictive than any one single estimate.
Using this average, and a variance determined by historical data, we are able to calculate a Beta distribution to model each team’s expected winning percentage for the upcoming season. We call this distribution a Prior Distribution, since it is calculated prior to collecting any data from the season.
After each game we increment the first parameter of the prior distribution by the number of wins a team has, and the second parameter by the number of losses. We call this a Posterior Distribution, since it is calculated after we have seen data from the regular season. The math behind how this works is fairly complex, but to be brief, the beta distribution and the binomial distribution are from the same distribution family and so behave well together. Read more about that phenomenon here.
Using the posterior distributions for each team, we calculated playoff probabilities and expected end of season win totals by performing Monte Carlo simulations. After 100,000 samples from the posterior distribution of each team, we get an average end of season win total, and can calculate playoff odds by seeing how often a team finished at the top of their division or in a wild card spot by comparing total projected regular season wins. Since a team’s current wins are “banked”, the sample from the posterior distribution is our estimate for rest of season performance.
How did these projections do at the Trade Deadline last year? Well for the American League, we had the Astros, Indians, Red Sox, and Yankees as locks to make the playoffs. The last wildcard spot we had going to either Seattle or Oakland, with Oakland eventually winning out. For the National League, we had the Cubs, Dodgers, and Brewers as locks, with the NL East being up for grabs between the Phillies and Braves, and the second wildcard being fought out between the Rockies and Arizona. Eventually, the Braves and Rockies would be the two teams to also make the playoffs. No team we gave less than a 10% chance of making the playoffs last year did, while every team over 95% (our locks) did make it into the gauntlet.
We think these projections are pretty good.
So how does this year look to end?
For the American League, our locks to make the playoffs are the Yankees, Astros, and Twins, the first two also being locks to win their division. If the Twins somehow fall to Cleveland, we still project them to make the Wild Card game. The last two playoff spots will go to two of four teams, the Indians, A’s, Rays, or Red Sox. We have the Indians vs A’s as the most likely Wild Card game. While the Indians are all but certain to make the playoffs as either winners of the Central, or as a wild-card, the second wild-card is completely up for grabs. The Red Sox and A’s keep switching positions in our model so who has the edge is anyone’s guess.
For the National League, we only have the Dodgers and Braves as locks.The NL Central is a mess, with both the Cubs and Cardinals projected to tie at 86 wins and the Brewers to come in third at 85. Regardless, the top wild card will probably go to the Nationals, with whomever fails to win the NL Central falling to the second wild card as a consolation prize.
If the season were to end exactly how we predicted, here is how our model has the playoffs:
Personally, I think that it is kind of ridiculous that some clubs are arguing that the Trade Deadline should be moved back to August 15th so they can truly see where their club is at.
Is your favorite team going to make the playoff? Do you disagree with any of our projections? Let us know in the comments below! As always, our code, data, and visuals can be found on our GitHub. Be sure to check back regularly as we update our MLB playoff odds and expected wins daily!
The SaberSmart Team
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