Thursday, March 9, 2023

How would the team with the highest OPS differential (1927 Yankees) do against the team with second highest OPS differential?

Last August I compiled the top 25 teams in OPS differential from 1901-2021. The 2022 Dodgers would tie for 4th place while the 2022 Astros would be tied for 15th. See Highest Team OPS Differentials, 1901-2021.

The 1927 Yankees are first with .197. If we only include full seasons, the 2019 Astros are 2nd with .167, then the 1939 Yankees and 2022 Dodgers (both at .158), then the 2019 Dodgers and 1902 Pirates (both at .149). So the 1927 Yankees are well ahead of the pack.

The 2020 Dodgers had .194 but that was only a 60 game season.

I wondered what this huge edge for the 1927 Yankees means mathematically. So the first thing I did was to estimate their winning pct. In regressions, the equation I get for pct is usually something like

Pct = .5 + 1.3*OPSDIFF

That would give the 1927 Yankees a .756 winning pct (in real life it was only .714 so they had some bad luck or bad timing). The 2nd place Astros would have .717 by this equation.

What winning pct might a .756 team have against a .717 team? For that, I turned to a Bill James formula called Log5 (and I think some of the credit also goes to a guy named Dallas Adams). The formula assumes that the two teams faced the same competition. That is not the case here, but all I want to know is what the mathematical difference is between the teams based on their respective OPS differentials.

Here is the formula for telling us the winning pct for team 1 (1927 Yankees) if they play a set of games against team 2 (2019 Astros)

PW1*(1-PW2) divided by PW1*(1-PW2) + PW2*(1-PW1)

PW1 is the Yankees winning pct (.756). PW2 is the Astros pct (.717). Plugging in those numbers, we get .550. So the 1927 Yankees are so much better than even the next best team (albeit only mathematically) that they would beat that team 55% of the time.

A .550 winning pct is 89 wins over 162 games and is not too far off from what it takes to come in first place or make the playoffs. Even against the next best team, the 1927 Yankees are close to contenders in a normal league.

Update March 11, 2023: I came across an interesting comment by Tangotiger at "Bill James Online." He showed a simpler way to estimate the winning pct that gets the same answer as Log5. See The Log5 Method, Etc, Etc, Etc..

"To show how the odds ratio method works, and how it gives the identical results to log5.

You have a .600 team (.6 wins per .4 losses or 1.5 wins ratio per loss) facing a .400 team (.4 wins per .6 losses or 0.67 wins ratio per loss).

When a .600 v .400, you would do:
1.5 / 0.67 = 2.25

That's 2.25 wins per 1 loss. To convert a ratio to a percentage:
2.25 / (2.25 + 1) = .692

Just like log5."

In this case, for the Yankees, they have 3.1 wins for every loss (.756/(1 - .756) =3.1). For the Astros it is 2.53 wins for every loss (.717/(1 - .717) = 2.53).

Then 3.1/2.53 = 1.22

Then 1.22/(1.22 + 1) = 1.22/2.22 = .550.

That is what I got using Log5.

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