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Rebuking of Clemens Statistics

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Rebuking of Clemens Statistics

Postby Matthias » Mon Feb 11, 2008 11:39 am

Four professors at Wharton (UPenn's business school) debunked Clemens' own, personal, 45-page report.

By comparing Clemens only to those who were successful in the second act of their careers, rather than to all pitchers who had a similarly successful first act, the report artificially minimizes the chances that Clemens’s numbers will seem unusual. Statisticians call this problem selection bias.

There is no doubt that Clemens was a great pitcher, but the question is whether he was much better past 36 or 37 (when he is suspected of having taken performance-enhancing drugs) than would have been expected based on his early career.

A better approach to this problem involves comparing the career trajectories of all highly durable starting pitchers. We have analyzed the progress of Clemens as well as all 31 other pitchers since 1968 who started at least 10 games in at least 15 seasons, and pitched at least 3,000 innings. For two common pitching statistics, earned run average and walks-plus-hits per innings pitched, we fitted a smooth curve to all the data from these 31 pitchers and compared it with those for Clemens’s career.

Relative to this larger comparison group, Clemens’s second act is unusual. The other pitchers in this durable group usually improve steadily early in their careers, peaking at around age 30. Then a slow decline sets in as they reach their mid-30s.

Clemens follows a far different path. The arc of Clemens’s career is upside down: his performance declines as he enters his late 20s and improves into his mid-30s and 40s.
0-3 to 4-3. Worst choke in the history of baseball. Enough said.
Matthias
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