Is there a "Rick Peterson" effect?  Does the Zen guru of pitching actually improve the performance of the pitchers he tinkers with?

A discussion at Baseball Think Factory (initially about Leo Mazzone) shows serious statistical analysis that indicates pretty strongly that Peterson has little measurable effect on pitchers' results.  (Mazzone, sorry to say, DOES apparently have a significant measurable effect on performance.)

http://www.baseballthinkfactory.org/files/primer/discussion/24762/P100

Other interesting reading on this topic: Hardball Times agrees with BTF,
http://www.hardballtimes.com/main/article/5questions_as/
while Beaneball begins to show a little doubt:
http://beaneball.org/index.php/2004/08/25/

I find the BTF analysis pretty convincing, though it's not definitive.  If Peterson does something for his charges, it doesn't seem to show up obviously in the numbers they put up.  And anyway, a lot of his reputation seems unearned (on the backs of the former Oakland Big Three, how bad would any pitching coach look?).  Most of the Peterson-is-a-god arguments are based on simple logical fallacies -- post hoc, ergo propter hoc; Peterson arrived/left, the numbers got better/worse -- and strike me as unconvincing in the face of the BTF analysis.  Can we give up hoping for Zambrano and Ishii to be better than Kazmir and Trachsel/Ginter/Seo/whoever now?