Re: A Realistic View at 2013: Part III
posted at 8/4/2013 1:09 PM EDT
In response to Hfxsoxnut's comment:
In response to zbellino's comment:
ERA+ is a measuer of how much better the league average pitches than the pitcher who is being measured.
ERA- is a park adjusted measure of how much better that pitcher is against the field.
ERA+ doesn't really make sense to me.
It's much easier to wrap your head around how one person fares against the average, than how well the average fairs compared to the pitcher.
Somebody better clarify the ERA+ and ERA- difference.
It seems to me that ERA+ is by far the more widely used. As I understand it, ERA+ is park-adjusted. Jake Peavy's career ERA+ of 115 indicates that he has been 15% better than average.
Sorry I'm trying to be clear. ERA+ isn't more widely used, it's the Baseball Reference stat. ERA- is the fangraphs stat.
Peavy's career ERA+ does not mean he has been 15% better than average. It means the the average has been 15% worse than Peavy. There is a difference.
His career ERA- of 86 means he has been 14% better than the league over his career. He allows just 86% of the league average pitcher's runs in that time.
ERA+ = 100*LgERA/ERA
ERA- = 100*ERA/LgERA
I was wrong, both are park adjusted. Neither are league adjusted.
A high ERA+ is better, a low ERA- is better.
EAR+ ... as you can see... tells you about how the league averages against the pitcher.
Remove the 100 from the formula and you are just producing a ratio expressed as a decimal *100.
If league avg ERA is 4 and your pitcher has an ERA of 3 then the *league* has an era of 1.33 of your pitcher, or really IT allows 133% of the runs your pitcher allows. Hence, your ERA+ would be 133.33~. It's not a measure of how your pitcher is better than the league ... it's a measure of how much worse or better the league is from your pitcher.
With ERA- if league average ERA is 4 and your pitcher's is 3 you reverse it. You get 3/4. Your pitcher has an ERA .75 of league average. Your ERA- would be 75 after the 100* multiplication ... more clearly expressed by saying ... your pitcher yields 75% the runs of a league average pitcher. Or his ERA is 25% better than the league's ERA.
The very concept of a.) measuring how your pitcher performs, and b.) having less runs be better ... is a LOT more transparent to me. It just makes more sense than having this high score of the league against your pitcher mean your pitcher is good.
In the end .... what is more clear? Considering allowing LESS runs is always better ... what is more clear? Saying that the league average pitcher gives up 4% more runs than Peavy? Or that Peavy is giving up 96% of the runs an average pitcher gives up?
In this case, his ERA+ is currently 104 and his ERA- is currently 96.