You might wonder if a guy who is able to maintain or improve his performance as he aged had a little help from steroids or some other chemical enhancer. You probabaly heard about Roger Clemens' agent writing a report to refute claims that he took steroids. JC Bradbury took a look at this and you can read what he had to say with What Do the Statistics Say about Roger Clemens’s Steroid Use?. The report by Clemens' agent can be read by clicking here. What I do here is to see how Clemens did from age 40-44 compared to how he did from 35-39 and then compare that to the performance changes of other pitchers over the same ages. All the data comes from the Lee Sinins Sabermetric Encyclopedia. I found the 53 pitchers who had at least 500 IP from 35-39 and 200+ IP from 40-44. In general, Clemens does much better at the older age. But he is not always first or close to first in the rankings of the various stats. (click here for part 2 of this study.)
I also wrote a couple of articles called "Did Roger Clemens Have the Best Age-Adjusted Season Ever in 2005?" (parts 1 and 2) a couple of years ago. You can read them here and here.
First, let's see who the best pitchers were past the age of 39. The following table shows the top 15 pitchers with 200+ IP. The 161 for Wilhelm means that he was 61% better than the average pitcher in ERA. Clemens is near the top. Wilhelm was a knuckleballer. Smoltz does not have that many IP. Lyons and Hevving were old during WW II. So Clemens really stands out.
The next table shows the increase or decrease in ERA relative to the league average going from the ages 35-39 to 40-44. Rogers had a 99 from 35-39, meaning he was 1% worse than average. He had a 119 when he was 40-44, meaning he was 19% better than average. Then 119/99 = 1.20. So taking the league average into account, Rogers was 20% better at the older age. Of course, Clemens is up there and has alot more IP than Rogers or Seaver.
The next table shows how much they increased or decreased in SO/BB ratio. Ryan has 30% at the older age. His SO/BB ratio was 2.25 at the younger age while the league average was 1.72. 2.25/1.72 = 1.30. So he was 30% better than average in the younger years. But he was 70% better than average during the older years. His SO/BB ratio was 2.95 while the league average was 1.74 (2.95/1.74 = 1.70). 1.70/1.30 = 1.30. That is why Ryan is 1st below at 1.30. Clemens does make the top 15. He was 5% better.
The next table shows the change in allowing HRs. In the younger years, Seaver gave up 93 HRs while an average pitcher would have given up 72. So Seaver gave up 29% more HRs (93/72 = 1.29). In the older years he gave up 39 while the average was 46. He gave up 15% fewer HRs than average (39/46 = .85). Since .85/1.29 = .66, Seaver's rate of giving up HRs at the older rate was just 66% that of his younger rate. Clemens also made the top 15 here.
The next table shows how many runs per 9 IP each pitcher gave up in the older years relative to his younger years. For this, I used a stat from the Lee Sinins Sabermetric Encyclopedia called RSAA which shows how many fewer runs a guy allowed than the average pitcher while adjusting for park effects. I first adjusted each guy to a league with 4 runs per 9 IP. Clemens has 3.10 runs per 9 IP at the younger age and 2.63 at the older age. Since 2.63/3.10 = .85, Clemens only gave up 85% as many runs at the older age than he did at the younger age.
The next table simply shows how the best pitchers in terms of how many more or fewer runs they saved at the older age compared to the younger age. Ryan gave up 21 fewer runs than average (park adjusted) at the younger age but 69 fewer at the older age. So he improved by 48. Very few guys saved more runs at the older age. Clemens does well here, too.
The last table just shows the leaders in terms of change in IP. Ryan was actually the only one to pitch more innings. There may be others who did, but they don't meet the qualifications I set out at the beginning.
(click here for part 2 of this study.)