Thursday, September 6, 2007

How extreme are the IBL's park effects?

Having quantified the differences between the IBL's parks, at least as a first estimate, I now wonder how the park factors compare with the major leagues. Do MLB parks vary as widely as the IBL's? My intuition would be to say no, that in the major leagues the ballparks are held to a higher standard of uniformity.

My intuition would appear to be somewhat wrong.

To start with the biggest variances in the IBL, home run factors range from 0.63 of average at Yarkon to 1.32 at Gezer. In the MLB (for 2006, the last complete season), home run factors range from 0.681 (AT&T Park, San Francisco) to 1.343 (Chase Field, Phoenix), about the same range as the IBL.

Triples - the most unreliable stat since it's such a rare event - range from 0.0 at Gezer to 1.94 at Yarkon. In the majors, the range is 0.4 (Great American, Cincinnati) to 2.0 (Rogers Centre, Toronto).

Overall hits, meanwhile, range from 0.94 at Yarkon to 1.06 at Sportek. In the MLB, it's 0.895 (Safeco Field, Seattle) to 1.14 (Coors Field, Denver) - a wider range. Same goes for runs: a narrow range of 0.99 to 1.03 in the IBL, compared with 0.86 (Petco Park, San Diego) to 1.15 (Great American, Cincinnati) in the MLB.

Of course, the variation in the majors is among thirty parks, not three, so the typical difference between MLB parks is much smaller than in the IBL. You could say that there is as much range of variation among the three IBL parks as there is among all thirty MLB parks. Though actually, judging by runs and hits, the IBL parks vary less than the MLB's.

I'm not going to calculate variances and standard deviations among sets of three figures, since I don't think they'd be meaningful, so I can't quantify the differences in ranges of park factors between the two leagues. But the IBL's situation is certainly not nearly as extreme as I had assumed.

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