RELIEVERS: Comparing ERA, xERA and projected xERA

This column will compare early-season actual ERA, expected ERA or xERA, and projected xERA. The difference between actual ERA and current xERA is that current xERA has the situation-dependent factors (such as bullpen support, park factors, etc.) stripped out so all that is left is the ERA based on the pitcher's own skill. There exists quite a bit of volatility between actual ERA and xERA when the sample size (innings) is so small. Therefore, we must still look to the projections for a better/historic view of what to expect in the future. As we know from the Baseball Forecaster, projected xERA is more accurate for looking ahead on a purely skills basis than projected ERA, which includes situation-dependent events. (See page 34 of the...

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