ERA
Description:
Earned Run Average (ERA) is a rudimentary metric designed to assess how well a pitcher has done in the past. To calculate, divide a pitcher’s total number of Earned Runs allowed by his total number of Innings Pitched and multiply by nine. ERA is not a good predictor of future success, as Earned Runs are dependent on multiple factors outside of the pitchers control: defense, umpiring, the judgment of a scorekeeper, etc. As a result, pitcher ERA rates vary significantly from year to year.
If you’re having trouble seeing the problems with ERA, consider this: according to ERA, a solo homerun hit off a hanging curveball is the same as three bloopers that drive in a run. Which is the better player, the pitcher that strikes out the side or the pitcher that relies on his rangy defense to haul in three deep fly balls?
Context:
2010 ERA Values
Things to Remember:
- ERA is difficult to compare across teams due to the variation of team defense; difficult to compare across leagues due to competition imbalance and the DH; and difficult to compare across years because of different run-scoring environments.
- ERA tends to be useful in very large (i.e. career long) samples, though ERA+ is better for those large samples.
Links for Further Reading:
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