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Saturday, April 23, 2005

Altitude Bias?

Since 1993 the Rockies have won 882 games and lost 999 putting them near the bottom (and not counting Arizona and Tampa Bay ahead of only Florida at 882 (who also has two World Championships), Kansas City at 841, Pittsburg at 835, Milwaukee at 825, and Detroit at 779 (Atlanta leads the pack at 1,149 wins followed by the Yankees and Giants). This level of mediocrity calls out for an explanation.

I first explored this topic and the common explanation offered by some Rockies players that there is a "hangover effect" as Rockies hitters adjust to hitting at sea level. Like others before me I didn’t find any evidence for such an effect.

After thinking about it a bit more I wondered if the effects of a team at this altitude were simply more systemic and rooted in how that team evaluates its players. In other words, could it be the case that the Rockies overvalue players because they look like above average performers based on the strength of their home splits? The cases of Vinny Castilla and Dante Bichette are at least anecdotal evidence that this may be the case (of course right now Vinny looks like a good pickup by the Nationals GM Jim Bowden but given his track record away from Denver I wouldn't expect it to last). This "altitude bias" may be enhanced by the fact that the Rockies AAA club plays right here in Colorado Springs at a slightly higher altitude.

For example, this springs the Rockies appeared to really be evaluating centerfielder Choo Freeman as a possible fourth outfielder. Last season Freeman hit .297/.350/.478 with the Sky Sox, which on another AAA team might translate into replacement-level offensive at the major league level. However, playing at 6,000 feet Freeman’s AAA translated or equivalent stats were .239/.290/.374 with a Value Over Replacement Player (VORP) of -6.5 and Marginal Value Lineup Rate (MLVR) of -.009. In other words, Freeman was below average in his league based on MLVR and therefore well below average at the major league level. Would other teams have even considered Freeman as a possible candidate given that his defense is below average and his history of stolen bases is abysmal (25 SB 24 CS at all levels since 2002)?

To test this theory I decided to make some blanket comparisons between offensive performance of players when in a Rockies uniform and those same players when playing with other teams. If the Rockies tend to overvalue mediocre offensive players, their performance on other teams should be worse than average performance when players leave other teams.

Here’s what I found (all numbers are only since 1993, BRA = OBP * SLUG and is a slightly better predictor of offensive production than OPS).

With COL .281 .340 .451 .791 .153
Not with COL .256 .321 .394 .715 .126

I then compared these numbers to other teams:

FLO .260 .327 .403 .729 .132
Not FLO .269 .332 .416 .749 .139

LAN .260 .325 .399 .723 .129
Not LAN .265 .335 .413 .748 .139

CHN .260 .322 .397 .719 .128
Not CHN .264 .326 .401 .727 .131

SLN .266 .333 .419 .752 .139
Not SLN .261 .325 .410 .734 .133

MIN .263 .327 .392 .719 .128
Not MIN .252 .317 .378 .695 .120

With the exception of the Twins, all the other team’s players performed better when leaving their teams than Rockies players did when leaving Denver. So does this result mean anything? I’d be hesitant to put too much weight on it but generally speaking it seems to hold. Rockies players don’t do quite as well when leaving Denver as other players do.

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