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Monday, February 22, 2010
Pitchers peak at age 29! Maybe, not?
I selected the 100 pitchers with the most innings pitched in 2006. I took the top 10 in ERA of those pitchers. Here they are, along with their ages:
ERA Age
2.77 27 Santana
2.98 29 Oswalt
3.09 31 Carpenter
3.10 22 Johnson
3.10 27 Webb
3.19 29 Halladay
3.22 26 Sabathia
3.24 22 Kazmir
3.29 29 Arroyo
3.41 25 Zambrano
The average age is 26.7. Here’s the top 10 in 2001:
ERA Age nameLast
2.49 38 Johnson
2.73 24 Oswalt
2.98 35 Schilling
3.04 37 Burkett
3.05 35 Maddux
3.05 26 Garcia
3.09 33 Kile
3.15 33 Mussina
3.16 26 Mays
3.16 27 Morris
The average age is 31.4.
I repeated this for every season from 1969-2009. The average age of the ERA leaders was 28.9 years old. Wow, you must be thinking. That must mean that pitchers peak at age 29! Well, what if I look at all 100 pitchers with the most IP each season, not just the top 10 in ERA of those 100? The average age is also 28.9.
That is, the age of the best pitchers matches the age of the population they were in. Indeed, you will typically find that if your sample is made up of a certain age group, then the age of peak performers and age of all performers will match.
For example, let’s say I only look at the age of peak performers who were at least 30 years old. So, in the 41 years of top 10 ERA leaders (410 pitchers in all), 202 were at least 29 years old. Their average age was 32.4. And for the young pitchers, there were 208 pitchers who were at most 28 years old, for an average of 25.6 years old. And if we looked at all 4100 pitchers? The population of old pitchers was 32.6 years old and the young pitchers was 25.6. See? Whatever the average age of your population is, that’s going to be the age of your peak performance as well.
Beware of this selection bias.
***
Here is the average age of the 100 pitchers with the most IP, and the age of the top 10 in ERA. As you can see, the young guys are starting to take over these last 4 years:
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