I’ve always thought of ERAs as somewhat akin to golf scores. Most of the scores are in the 4’s and 5’s. A 3-something is really outstanding. And any kind of 6 on your scorecard means it’s time to start thinking about playing golf … wait, that doesn’t work.
Of course, these scores are meaningless without knowing how the hole plays. A 6 on a par-5 is nothing too out of the ordinary; a 6 on a par-3 is a John Daly style meltdown. The same is true for ERAs.
Take Ted Lilly, for example. PECOTA projects his ERA for next year as 4.90 — as a Toronto Blue Jay. As a Yankee, 4.65. As a Chicago Cub, it’s 4.36. And as a San Francisco Giant, 4.08. With the higher of those numbers, the expensive new contract he’s about to sign would be described as a complete failure; with the lower of those numbers, a reasonable success. Same pitcher, same performance, different perceptions.
Not that I’m breaking any news here; adjusting statistics for context gets back to sabermetric first principles. But this context becomes even more important in light of another sort of adjustment that we have to make: accounting for the substantial disparity in quality between the American and National leagues. Specifically, PECOTA — which is accounting for league difficulty for the first time — figures that the NL is about 25 points of ERA “easier” than the AL. This is above and beyond any adjustments for the designated hitter, which move in the same direction.
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