Weinberg: ERA, FIP, and answering the right question
From Neil Weinberg at FanGraphs on August 15, 2014:
One of the things baseball fans and analysts work very hard to do is isolate individual performance. At the end of a game, there is a final score that tells you how many runs each team scored. At a very basic level, that’s all that really matters. Baseball is a battle to score more runs than your opponent over the span of nine innings repeated 162 times. Yet analyzing the game requires more information than that because we want explanations. We want to know which players are good and which players aren’t so good. We care about how individual performance contributes to winning.
For pitchers, this is especially difficult because while pitchers have a huge impact on the number of runs they allow, they don’t have complete control. You can’t just look at the number of runs a pitcher allowed and say they were definitively responsible for those runs and call it a day. You aren’t isolating their performance and if you aren’t isolating individual performance you’re looking only at outcomes, and that’s not typically very interesting.
Every statistic, or really any analysis in general, should start with a question. On a basic level, the question we have is “How good is this pitcher?” which more specifically translates into “How effective is this pitcher at preventing runs?”
Typically, most fans and commentators turn to Earned Run Average (ERA) to answer this question. This tells you how many earned runs a pitcher allows per nine innings. It seems to answer the question we’ve posed, but it actually doesn’t. It’s a bit of a trap, largely because it has a sneaky name.
Read the full article here: http://www.fangraphs.com/library/era-fip-and-answering-the-right-question/
Originally published: August 15, 2014. Last Updated: August 15, 2014.