Sabernomics: What Do the Statistics Say about Roger Clemens’s Steroid Use?

Fresh from taking in an FDA Epitonine game...JCB digs deep into the Clemens statistical report.

Clemens’s study looks at his performance in reference to the changing playing environment of the league. For many potential reasons (e.g., new ballparks, expansion, juiced balls, etc.) the run environment dramatically changed over the course of Clemens’s career. To combat any bias from this, the authors of the study compare Clemens’s ERA to the average of the league, looking at the difference. It is no surprise that his ERA difference fluctuated quite a bit over the course of his career (p. 6). ERA is inherently a volatile statistic. In fact, in my book I use Clemens as an example of how drastically a pitcher’s ERA can change during a career, and I show that his variation in performance was well within the normal range (p. 165).

What I would like to do is to take this analysis one step further. One of the reasons that ERA is volatile is that it includes the performance of fielders and random bounces of the ball. If we use the novel idea of Voros McCracken’s DIPS, then we can more closely examine the components of Clemens’s performance over his career using factors that were solely in his control. The major defense-independent components of pitcher performance are strikeouts, walks, and home runs. In particular, I would expect Clemens’s strikeout numbers to influence and reflect his decision to use performance-enhancing drugs. Because these statistics occur at different rates, I compare how Clemens performed relative to the league average as percent of the league average.

...This in no way proves that Clemens didn’t use steroids; he is right when says he can’t prove a negative. Others may interpret the data differently than I do. But, the more I look into these numbers, the more I am convinced that McNamee is the one who is lying. Until I see some other corroborating evidence—I wonder what is in those seized 2004 drug tests—I have to conclude that Clemens pitched without the aid of steroids.