Attention All Miley Apologists

[AdamDunn#44]

The Reds horrible pitching makes the GAB look like Coors Field.

It's a decent park to pitch in ya have good pitchers.

[Wally Mo Pena]

The sample size is too small for GABP still, but overall i think it's a good park to hit HRs in, espectially if you are left handed, but it's hard to hit grounders through the infield and maybe the ball doesn't carry in the gaps.

This article from BP talks about how park factors can change:

One of the principal tenets of performance analysis is the idea that a player's statistics are affected by his home ballpark. That's why most serious performance metrics account for the environment in which a player plays using a park factor. This park factor is generally arrived at by comparing the number of runs scored in all games in team's home park and comparing that to the number of runs scored in that team's road games.

I have found that there is good reason to doubt the value of these park factors in a single season. I believe the relative ease or difficulty in hitting in a specific park has a large random aspect, and hence much less weight should be put on park factor for any single season.

This is important for people who calculate, for example, that the performance of Hitter A in any given year was more valuable than that of Hitter B, based on his Equivalent Average or Value Over Replacement Player (VORP). That is, if A played in a home ballpark with a calculated park factor of 105 and B played in a ballpark with a 95 park factor and their performances were comparable, many sabermetric stats will conclude that player B was more productive. But if there is a degree of randomness--call it an error rate--in ballpark factors of five percent or more, there is a chance that in fact each player played in a neutral park.

How can it be that park factors could be off by so much? The answer is limited sample size. A park factor for any given year is based on only 81 home games. In many seasons, some teams will play even fewer (due to non-rescheduled rain-outs and so on). Eighty or so games are not enough to eliminate a large error rate. A park with a park factor of 95 one year and 100 the next very likely cannot be said to be relatively easier to hit in the second year. Instead, it is fair to conclude that by random chance, there was a five percent differential in the two seasons (assuming that major changes did not occur with other home parks in the league).

Over 10 or 15 years, the error rate becomes much smaller as the sample size increases. Unfortunately, it is problematic to average out a park factor over more than a few years because the conditions of one or more of the ballparks in a league change. New stadiums are built, existing stadiums change their dimensions, and abnormal weather patterns have an impact. Nonetheless, a 10-year sample is likely to be more accurate than a one-year accounting.

Let's look at some examples. Excepting 2000, which looks like "an aberration," Oriole Park at Camden Yards appears to be a very average facility to hit in, with only a very slight edge to the pitchers. From 1996-1999, its ballpark factor averaged 98.25, almost exactly average:


1996: 99
1997: 97
1998: 98
1999: 99
2000: 95

But from 1992 through 1995, the first four years of its life, Camden Yards was actually a decent hitters' park, averaging a PF of 104:


1992: 103
1993: 103
1994: 105
1995: 105

What happened to change the personality of Oriole Park? The obvious answer is that after 1995, a number of new ballparks came on line and caused the relative ease of hitting in Camden Yards to go down. Now, The Ballpark in Arlington and Jacobs Field--both renowned as hitters' parks--came to life in 1994. Yet in 1994 and 1995, Camden Yards was much more friendly to hitters than were either.

click here for the rest:
http://www.baseballprospectus.com/ar...?articleid=897