Component ERA
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Component ERA (ERC) is a baseball statistic invented by Bill James. It attempts to forecast a pitcher's Earned Run Average or ERA from the number of hits and walks allowed rather than the standard formula of average number of earned runs per nine innings. ERC allows one to take a fresh look at a pitcher's performance and gauge if his results are more or less than the sum of its parts.
The formula for ERC as it appears in the 2004 edition of the Bill James Baseball Abstract:
ERC=(((H+BB+HBP)*PTB)/(BFP*IP))*9-.56
PTB, defined:
PTB=.89*(1.255*(H-HR)+4*HR)+.56*(BB+HBP-IBB)
Where intentional walk data are not available use:
PTB=.89*(1.255*(H-HR)+4*HR)+.475*(BB+HBP)
If ERC is less than 2.24, the formula is adjusted as follows:
ERC=(((H+BB+HBP)*PTB)/(BFP*IP))*9*.75
Other people and organizations have their own proprietary formulae for ERC which may correlate more highly with actual earned runs scored than the formula above.
[edit] Inferences Drawn
It should be noted that only once during his 21 year Major League career did John Franco have an ERC lower than his ERA. This may be due to his propensity to allow a high percentage of inherited runners to score.
