Baseball By The Numbers—Earned Run Average (ERA) and Fielding Independent Pitching (FIP)


The first two installments of my series on baseball statistics focused on offense.  This post will discuss two measurements of pitching, Earned Run Average (ERA) and Fielding Independent Pitching (FIP).  ERA is a well known statistic, FIP, much less so.  ERA measures the mean of runs given up by a pitcher per nine innings pitched.  FIP measures what the ERA should have been when factors out of the pitcher’s control, such as the performance of defense, and luck, are taken out of the equation.

St. Louis Cardinals starting pitcher Adam Wainwright (50) receives a new ball during the 2012 NLDS against the Washington Nationals at Busch Stadium. Mandatory Credit: Jeff Curry-USA TODAY Sports

ERA is calculated by multiplying the number of earned runs allowed by a pitcher by 9 and the dividing that number by the number of innings the pitcher pitched.  Runs occurring as a result of defensive errors are not included in the calculation.  An ERA below 4.00 is considered good, an ERA below 3.00 is considered excellent.  ERA as a measure of a pitcher’s performance is limited, because it takes into account factors that are beyond the control of the pitcher, such as the fielding of balls in play, the ball park the pitcher is pitching in, and the effect of luck.

FIP is a statistic that eliminates factors that are beyond the control of the pitcher. FIP also weights the factors that are under the pitcher’s control.  Home runs are the most harmful and thus are weighted the highest, walks and hits by pitches are weighted the same and strikeouts are weighted less than all.  The formula for FIP is ( (13 x HR) + 3 x (BB +HBP) ) – 2 x K /IP + constant.  The constant is the league average ERA minus the league average FIP, which is generally around 3.20.  A FIP of 4.00 is considered average;  a FIP of between 2.95 and 3.25 is considered excellent.  FIP is a better statistic for measuring performance over a large sample size, such as a full season, rather than for a single game performance.

I will be using two Cardinal starting pitchers, Adam Wainwright and Kyle Lohse, to demonstrate the difference between ERA and FIP.  For the 2012 season, Wainwright had an ERA of 3.94 and a FIP of 3.10.  Lohse had a 2012 ERA of 2.86 and a FIP of 3.51. Wainwright’s ERA, while below 4.00, was not as good as it has historically been and was higher than that of Lohse.  However, Wainwright’s FIP was excellent.  Lohse, on the other hand, had a lower and better ERA than Wainwright, but a worse FIP.  Lohse’s FIP was not bad, it was still above average, but it was not nearly as good as Wainwright’s.   What these numbers tell us generally is that Wainwright’s ERA was negatively affected by factors out of his control; poor defense and bad luck.  Lohse, on the other hand, benefited from those same factors.  One way we can know what effect luck had is to look at another statistic, BABIP (batting average on balls in play) which I will cover more thoroughly in another post, but which among other things measures the effect of luck.  Wainwright’s BABIP against was .315; Lohse’s was .262.  This means Lohse had better luck with balls in play than Wainwright did.

While ERA is historically the statistic used to measure pitcher performance, FIP is actually a much better and more accurate measurement.  What this tells us is that when evaluating a pitcher, it would be wise to consider more than just ERA, as ERA has limitations.  Looking at both ERA and FIP gives the observer a much better snapshot of how good a pitcher has been than ERA alone.