When we evaluate the Astros’ pitchers for the 2025 season, it’s natural to look back at their earned runs allowed per nine innings (ERA) in 2024. And, yes, that’s a starting point. But ERA, by its nature, is a “noisy” statistic. A bunch of random things can distort the ERA in a given season. Factors like the quality of defense behind the pitcher, sequencing of hits, quality of contact—and the list could go on—involve some degree of luck.
That’s why the pitchers’ 2024 ERA is a weak predictor of next season’s ERA. Sure it likely has some correlation to the next season’s ERA, but the error band around the prediction will likely be large.