Component ERA

Component ERA (ERC) is a Bill James statistic that estimates a pitcher's ERA based on his peripheral statistics rather than the runs allowed (since the number of runs can be biased by the next pitcher allowing the first pitcher's runners to score and plain old luck). The term is sometimes used more generally to refer to any method with the same objective.

James' ERC is based on the Runs Created model of run scoring, and is calculated as follows:

ERC = (H + W + HB)*PTB*9/(BFP*IP) - .56

where PTB = .89*(1.255*(H - HR) + 4*HR)+.56*(W+ HB - IW)

If the result of (H + W + HB)*PTB*9/(BFP*IP) is less than 2.24, then instead of subtracting .56, multiply by .75.

A study by Cyril Morong ("The Accuracy of Component ERA" ) looked at 70 pitchers who pitched 3000+ innings between 1920 and 2000 and found "that 84.3% of the variation in ERA across pitchers could be explained by their component ERA."