Wait, why does PML favor the Astros?

After four games, this World Series is tied at two games apiece and shaping up for an exciting finish! According to our PML model, Houston has a 53% chance of winning it all. This might come as a surprise; the majority of other prediction models, like FiveThirtyEight’s Elo ratings, give Los Angeles a slight 56% edge—not surprising, given the Dodgers play two of the three games at home. In contrast, PML favors the away team in every game from here on out. Ultimately, the difference between the 44% chance FiveThirtyEight gives the Astros and our 53% is not huge. Whichever you prefer, the Series is a toss-up. But it’s useful to dig into why we’re a bit higher on the Astros, and in the process, get to know our PML model a little better.

A quick refresher: the PML model gives each starting pitcher and each offense a score. Multiplying a pitcher score by an offense score gives the number of runs we’d expect that offense to score in a game started by that pitcher. Since the scores relate to runs, a higher score is better for an offense. The opposite is true for a pitcher. With that in mind, let’s dig into these scores. (There’s more going on under the hood, but that’s all you need to know for this article.)

PML gives the Astros the best offense score of any team, while it scores the Dodgers as merely above average. It may be underrating the Dodgers a bit by using runs rather than underlying offensive stats. Los Angeles is 11th in baseball in PML and 12th in runs scored, but they ranked fourth in wRC+. Nevertheless, the offensive scores favor the Astros pretty heavily.

The Astros may have the best offense, but the Dodgers have the best pitcher. Clayton Kershaw has the lowest PML score of any pitcher, far and away the best of any starter for games five through seven. The second-best is his game five opponent, Dallas Keuchel, but the gap is significant. In game six, Justin Verlander has a slight advantage over Rich Hill, and if necessary, Yu Darvish would hold a slight game seven advantage over Lance McCullers, his likely opponent.

When combined, the offense and pitcher scores give an idea of how many runs PML expects each team to score.

So why does PML favor the Astros? Their high offense score holds sway in games six and seven, overshadowing both the home-field adjustment and the small differences in pitcher scores. The only thing able to keep Houston’s bats in check, according to PML, is Clayton Kershaw. He’s enough to lead PML to favor Los Angeles in game five, even with their explosive offense and home-field advantage.

Ultimately, with three games left in the 2017 baseball season, the World Series winner is still a toss-up. It should make for exciting baseball, so happy watching!

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