The Impact of ERA
Everybody knows that a pitcher with an ERA of 3.00 is better than a pitcher with a 3.50 ERA . We know the former pitcher is better, but by how much? How many more wins would a 3.00 ERA pitcher contribute to the team than a 3.50 ERA pitcher? These are questions I do not yet know the answer to, but I am interested to find out. Let's begin.
The first thing we must know to answer the presented questions is the formula for ERA, It is simple and most of you probably know what it is:
A simple enough equation, if we know the ERA and the amount of innings pitched, we can determine the amount of total earned runs that were given up. Fill in different ERAs into the equation while keeping the IPs the same will tell us the difference in total Earned Runs given up.
It is widely accepted that 10-11 runs is about equal to one win, so that is the conversion factor I will use to convert runs to the desired metric wins. I have a feeling that the aforementioned conversion factor will be revised to be made more accurate in the future, but it will work for my purposes now.
Going back to the task at hand, let's find out the Earned Runs difference for a pitcher who has thrown 200 innings by plugging the numbers into the above equation.
We will begin with the original example of a 3.00 ERA and 3.50 ERA pitcher. For a 3.00 ERA and 200 innings, the amount of Earned Runs given up is 66.67. For the 3.50 ERA it is 77.78. The difference between the two is 11.11 Runs, a number close enough to ten to call it about 1 Wins difference.
The difference between the two ERAs was .50 points. I would like to find out if the 11.11 run difference appears with all ERAs .50 points apart accumulated over 200 innings. I will use the ERAs of 4.00 and 4.50 to test this out. Over the same 200 innings an ERA of 4.00 would mean 88.89 total Earned Runs given up. For a 4.50 ERA, exactly 100 Runs would be allowed. The difference is. . . . . 11.11 Runs! That means in our context-neutral study of ERA, the difference between a 2.00 and 3.00 ERA is exactly the same as the difference between a 5.00 and 6.00 ERA.
Now that you know the procedure, I'll just spit out the data tables:
These tables read as follows --- for two pitchers having thrown 75 Innings, with the difference between them in ERA 1.00 point of ERA, the difference in Earned Runs allowed is 8.34 Runs or about .8 Wins.
There are some interesting revelations from these tables. One I expected was that the run differentials and win values over 100 innings is exactly half of the run differentials and win values over 200 innings. I'll leave you to peruse over them and perhaps you will find something interesting yourself.
If you enjoyed this article, good news for you, next week I plan on doing something similar. Instead of keeping the Innings Pitched a constant and varying the difference in ERA, I'll do the exact opposite. By holding the difference in ERA constant and varying the Innings Pitched, you can determine exactly how much more value a 200-Inning starter gives a team than a 75-Inning reliever with the same ERA over a season. See you then.
The first thing we must know to answer the presented questions is the formula for ERA, It is simple and most of you probably know what it is:
A simple enough equation, if we know the ERA and the amount of innings pitched, we can determine the amount of total earned runs that were given up. Fill in different ERAs into the equation while keeping the IPs the same will tell us the difference in total Earned Runs given up.It is widely accepted that 10-11 runs is about equal to one win, so that is the conversion factor I will use to convert runs to the desired metric wins. I have a feeling that the aforementioned conversion factor will be revised to be made more accurate in the future, but it will work for my purposes now.
Going back to the task at hand, let's find out the Earned Runs difference for a pitcher who has thrown 200 innings by plugging the numbers into the above equation.
We will begin with the original example of a 3.00 ERA and 3.50 ERA pitcher. For a 3.00 ERA and 200 innings, the amount of Earned Runs given up is 66.67. For the 3.50 ERA it is 77.78. The difference between the two is 11.11 Runs, a number close enough to ten to call it about 1 Wins difference.
The difference between the two ERAs was .50 points. I would like to find out if the 11.11 run difference appears with all ERAs .50 points apart accumulated over 200 innings. I will use the ERAs of 4.00 and 4.50 to test this out. Over the same 200 innings an ERA of 4.00 would mean 88.89 total Earned Runs given up. For a 4.50 ERA, exactly 100 Runs would be allowed. The difference is. . . . . 11.11 Runs! That means in our context-neutral study of ERA, the difference between a 2.00 and 3.00 ERA is exactly the same as the difference between a 5.00 and 6.00 ERA.
Now that you know the procedure, I'll just spit out the data tables:
These tables read as follows --- for two pitchers having thrown 75 Innings, with the difference between them in ERA 1.00 point of ERA, the difference in Earned Runs allowed is 8.34 Runs or about .8 Wins.
There are some interesting revelations from these tables. One I expected was that the run differentials and win values over 100 innings is exactly half of the run differentials and win values over 200 innings. I'll leave you to peruse over them and perhaps you will find something interesting yourself.
If you enjoyed this article, good news for you, next week I plan on doing something similar. Instead of keeping the Innings Pitched a constant and varying the difference in ERA, I'll do the exact opposite. By holding the difference in ERA constant and varying the Innings Pitched, you can determine exactly how much more value a 200-Inning starter gives a team than a 75-Inning reliever with the same ERA over a season. See you then.
