Saturday, May 16, 2009

Lies, damn lies, refuted by statistics

According to the early reviews, Selena Robert's new book paints a rather unflattering picture of Yankees' third-baseman Alex Rodriguez. Aside from accusing A-Rod of having taken steroids since high school, Roberts alleges that Rodriguez and other opposing players tipped pitches during blow-outs; knowing what pitches were coming, they could improve their statistics.

Unfortunately, Roberts has little more than anonymous sources to support her story. So baseball statisticians had to delve into past seasons in order to find evidence of A-Rod's malfeasance. The stats cast doubt on Robert's allegations:
"If a tipping conspiracy were in place, one would expect that Rodriguez and rival middle infielders in games he played to have hit better in low-leverage situations than in high-leverage ones. Using a fairly loose definition of high leverage as a L.I. above 1.5 and low leverage as below 0.7, the data provide a resounding answer: either no tipping was going on or it was pathetically ineffective.
Contrary to his reputation as a choker, Rodriguez was actually at his best when the game was on the line as a Ranger. According to data compiled by Sean Forman of, his combined on-base and slugging percentages (O.P.S.) from 2001 to 2003 was 1.076 in high-leverage situations, compared with 1.017 for medium leverage and .982 in low leverage. Opposing second basemen and shortstops showed the same pattern. They registered an .899 O.P.S. when leverage was high, .825 when it was middling, and .817 when it was low. Unless Rodriguez’s behavior was even more nefarious — tipping only when it mattered most — the numbers give no reason to believe he was involved.

Using a more stringent definition of blowouts yields the same result. In plate appearances in which the teams were separated by seven runs or more, Rodriguez mustered just a .851 O.P.S., compared with 1.021 when the margin was six or fewer runs. His middle infield counterparts compiled a .744 mark in the laughers and .840 the rest of the time."
Of course, we should not mistake absence of evidence for evidence of absence. It is possible that A-Rod tipped pitches on rare occasions; rare enough that one or two extra home-runs wouldn't show up in this kind of analysis. But this does provide strong evidence against the possibility that this kind of behavior was widespread. That conclusion may not restore our collective innocence, but it's nice to know.

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