Earned Run Average - Sabermetric Treatment of ERA

Sabermetric Treatment of ERA

In modern baseball, sabermetrics uses several defense independent pitching statistics including a Defense-Independent ERA in an attempt to measure a pitcher's ability regardless of factors outside his control. Further, because of the dependence of ERA on factors over which a pitcher has little control, forecasting future ERAs on the basis of the past ERAs of a given pitcher is not very reliable and can be improved if analysts rely on other performance indicators such as strike out rates and walk rates. For example, this is the premise of Nate Silver's forecasts of ERAs using his PECOTA system. Silver also developed a "quick" earned run average (QuikERA or QERA) to calculate an ERA from peripheral statistics including strikeouts, walks, and groundball percentage. Unlike peripheral ERA or PERA, it does not take into account park effects. Another statistic derived from ERA is Adjusted ERA, also called ERA+, which adjusts a pitcher's ERA to a scale where 100 is average for the league and takes into account the various dimensions and other factors of each ballpark.