Mains: 100,000 leagues under the PECOTA

From SABR member Rob Mains at Baseball Prospectus on March 19, 2020:

Flip a coin ten times and you’ll probably come up with a combination of heads and tails. Probably. But not always. On rare occasions, you might get heads ten times in a row. The odds of it are 1 in 1,024. Your chances of getting ten consecutive heads are small, but not vanishingly so. It’s entirely possible. You want to know what’s almost impossible? The odds of winning Powerball are 1 in 292,201,338. Your chances of getting heads 28 times in a row are better. But people still play Powerball. They’re not dissuaded by the odds.

That’s because sometimes really unlikely events occur. I might finish this article with no typos. MLB might conclude its investigation of the Red Sox. You might win Powerball. Even the unlikeliest events have a probability greater than zero.

Here at BP, we calculate projected standings using PECOTA, our proprietary model. But PECOTA, like all projection systems, has error bars. When we produce projections for a team’s win total, or a player’s OPS, we’re not saying they’ll hit it exactly. Rather, we were saying that’s the likeliest outcome. Each estimate has an implied plus-or-minus factor. Stack a few of those pluses and minuses atop one another, and you can get some pretty big outliers.

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Originally published: March 19, 2020. Last Updated: March 19, 2020.