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The Pitfalls of Park Factors

Trying to Make Useful Park Factors

(This is going to be a long page because of all the data displays; be patient.
Also, you may need to drag your browser window wider to fit all the wide tables.)

How to Go About It

As a simple demonstration of the issues, let's try to make a "park factor" for the simplest and most basic stat of all: runs scored. What we are looking for is some one number for a given ball park that will tell us how much easier or harder it is to score runs there than at an imagined "perfectly average" ball park.

To begin with, it should be obvious that the sample size in inter-league play is so small, and the complications from use or non-use of the DH Rule so aggravating, that we must needs restrict ourselves to trying to measure parks relative only to other parks in the same league. Fine: given that, what next?

The first principle is that we need to give parks equal weight in constructing our basis, the presumed "all-average" league park; but equal weight is something the schedule does not provide. A team might play as few as 5 games with some other team, or as many as 18 (and the number of home and away games against a given opponent need not be equal); so to deal with those issues, we need to measure not runs per se, but runs per game.

The next principle is that we need to compare like with like. How Team X does in scoring runs in Park Y and in Park Z depends not only on the characteristics of Parks Y and Z but also on the quality of the pitching staffs of Teams Y and Z. So we need to consider pairings: Team X against Team Y at Park X and at Park Y. Fortunately, we can double our sample size by also considering runs allowed by Team X against Team Y, because we are still comparing apples and apples (X vs. Y).

Another point in avoiding apples-and-oranges situations is changes in parks (or, nowadays, wholly new parks coming on line). For now, let's thus confine ourselves to a single season. For this example, we'll use the 2008 season.

A Typical Season's Raw Data

If we first look at the raw data (excluding inter-league games), it looks like this:


  
    Base Team / playing
    ari
    atl
    chc
    cin
    col
    fla
    hou
    lad
    mil
    nym
    phi
    pit
    sdg
    sfo
    stl
    was
  
  
    ARI
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
    
---
---
---
---
     
4
49
4
38
     
3
29
3
23
     
3
13
3
22
     
9
96
9
80
     
3
24
6
32
     
3
33
3
0
     
9
94
9
69
     
4
41
3
0
     
3
30
3
31
     
4
45
3
34
     
3
26
4
29
     
9
84
9
76
     
9
69
9
77
     
3
31
4
38
     
3
20
3
19
  
  
    ATL
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
38
4
49
    
---
---
---
---
     
3
38
3
29
     
3
33
3
28
     
3
35
4
36
     
9
93
9
89
     
3
28
3
29
     
3
19
3
18
     
6
38
3
15
     
9
89
9
74
     
9
79
9
106
     
3
42
4
26
     
3
24
3
24
     
4
31
3
26
     
4
48
3
42
     
9
101
9
82
  
  
    CHC
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
23
3
29
     
3
29
3
38
    
---
---
---
---
     
9
88
6
62
     
4
48
2
19
     
4
34
3
25
     
9
86
8
52
     
3
11
4
26
     
9
104
7
62
     
2
17
4
50
     
4
30
3
27
     
9
91
9
113
     
4
39
3
31
     
3
25
4
36
     
6
61
9
67
     
3
36
3
17
  
  
    CIN
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
22
3
13
     
3
28
3
33
     
6
62
9
88
    
---
---
---
---
     
3
26
3
33
     
4
48
4
53
     
6
66
9
66
     
5
43
3
23
     
9
78
9
77
     
4
46
3
37
     
4
37
4
21
     
9
96
6
35
     
3
31
4
45
     
3
43
3
34
     
9
78
6
64
     
4
27
3
29
  
  
    COL
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
80
9
96
     
4
36
3
35
     
2
19
4
48
     
3
33
3
26
    
---
---
---
---
     
4
79
4
34
     
3
22
3
31
     
9
106
9
72
     
3
24
4
40
     
6
48
3
13
     
2
28
3
43
     
4
37
3
33
     
9
109
9
68
     
9
82
9
72
     
4
41
3
17
     
4
41
3
35
  
  
    FLA
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
6
32
3
24
     
9
89
9
93
     
3
25
4
34
     
4
53
4
48
     
4
34
4
79
    
---
---
---
---
     
3
31
3
27
     
3
35
4
31
     
3
20
3
15
     
9
82
9
73
     
9
79
9
97
     
3
30
2
19
     
3
32
3
22
     
3
33
3
24
     
4
26
3
17
     
9
84
8
94
  
  
    HOU
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
33
3
33
     
3
29
3
28
     
8
52
9
86
     
9
66
6
66
     
3
31
3
22
     
3
27
3
31
    
---
---
---
---
     
4
30
3
26
     
6
71
9
79
     
3
23
4
34
     
4
47
3
22
     
7
71
9
74
     
2
31
4
27
     
4
39
4
40
     
9
75
6
40
     
3
29
3
25
  
  
    LAD
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
69
9
94
     
3
18
3
19
     
4
26
3
11
     
3
23
5
43
     
9
72
9
106
     
4
31
3
35
     
3
26
4
30
    
---
---
---
---
     
3
27
3
27
     
3
28
4
38
     
4
38
4
32
     
3
32
4
48
     
9
93
9
62
     
9
58
9
72
     
3
14
3
30
     
3
13
3
25
  
  
    MIL
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
26
4
41
     
3
15
6
38
     
7
62
9
104
     
9
77
9
78
     
4
40
3
24
     
3
15
3
20
     
9
79
6
71
     
3
27
3
27
    
---
---
---
---
     
3
28
3
30
     
2
13
4
36
     
9
84
6
51
     
4
24
3
20
     
3
33
3
34
     
6
58
9
70
     
4
28
4
33
  
  
    NYM
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
31
3
30
     
9
74
9
89
     
4
50
2
17
     
3
37
4
46
     
3
13
6
48
     
9
73
9
82
     
4
34
3
23
     
4
38
3
28
     
3
30
3
28
    
---
---
---
---
     
9
71
9
92
     
3
35
4
25
     
3
25
4
23
     
3
22
3
35
     
3
37
4
46
     
9
91
9
90
  
  
    PHI
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
34
4
45
     
9
106
9
79
     
3
27
4
30
     
4
21
4
37
     
3
43
2
28
     
9
97
9
79
     
3
22
4
47
     
4
32
4
38
     
4
36
2
13
     
9
92
9
71
    
---
---
---
---
     
3
17
3
29
     
3
22
3
15
     
3
27
3
28
     
3
13
6
61
     
9
83
9
78
  
  
    PIT
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
29
3
26
     
4
26
3
42
     
9
113
9
91
     
6
35
9
96
     
3
33
4
37
     
2
19
3
30
     
9
74
7
71
     
4
48
3
32
     
6
51
9
84
     
4
25
3
35
     
3
29
3
17
    
---
---
---
---
     
4
40
3
21
     
3
31
3
37
     
8
99
9
99
     
3
29
4
44
  
  
    SDG
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
76
9
84
     
3
24
3
24
     
3
31
4
39
     
4
45
3
31
     
9
68
9
109
     
3
22
3
32
     
4
27
2
31
     
9
62
9
93
     
3
20
4
24
     
4
23
3
25
     
3
15
3
22
     
3
21
4
40
    
---
---
---
---
     
9
60
9
64
     
3
29
4
50
     
3
23
3
32
  
  
    SFO
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
77
9
69
     
3
26
4
31
     
4
36
3
25
     
3
34
3
43
     
9
72
9
82
     
3
24
3
33
     
4
40
4
39
     
9
72
9
58
     
3
34
3
33
     
3
35
3
22
     
3
28
3
27
     
3
37
3
31
     
9
64
9
60
    
---
---
---
---
     
4
42
3
25
     
3
20
4
31
  
  
    STL
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
38
3
31
     
3
42
4
48
     
9
67
6
61
     
6
64
9
78
     
3
17
4
41
     
3
17
4
26
     
6
40
9
75
     
3
30
3
14
     
9
70
6
58
     
4
46
3
37
     
6
61
3
13
     
9
99
8
99
     
4
50
3
29
     
3
25
4
42
    
---
---
---
---
     
3
21
3
31
  
  
    WAS
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
19
3
20
     
9
82
9
101
     
3
17
3
36
     
3
29
4
27
     
3
35
4
41
     
8
94
9
84
     
3
25
3
29
     
3
25
3
13
     
4
33
4
28
     
9
90
9
91
     
9
78
9
83
     
4
44
3
29
     
3
32
3
23
     
4
31
3
20
     
3
31
3
21
    
---
---
---
---
  




  
    Base Team / playing
    bal
    bos
    chw
    cle
    det
    kan
    laa
    min
    nyy
    oak
    sea
    tam
    tex
    tor
  
  
    BAL
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
    
---
---
---
---
     
9
91
9
98
     
5
47
4
31
     
4
41
4
57
     
4
49
3
45
     
4
47
4
31
     
3
35
6
49
     
3
42
3
25
     
9
92
9
87
     
2
19
3
20
     
4
35
6
57
     
9
91
9
104
     
6
84
3
22
     
9
81
9
97
  
  
    BOS
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
98
9
91
    
---
---
---
---
     
3
24
4
33
     
4
32
2
18
     
3
32
4
39
     
4
38
3
27
     
6
66
3
28
     
3
35
4
47
     
9
92
9
94
     
3
24
7
48
     
3
25
6
35
     
9
79
9
75
     
7
102
3
41
     
9
66
9
85
  
  
    CHW
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
31
5
47
     
4
33
3
24
    
---
---
---
---
     
9
93
9
83
     
9
94
9
89
     
9
95
9
95
     
6
41
4
33
     
10
114
9
86
     
3
37
4
31
     
6
35
3
27
     
3
41
3
27
     
3
32
7
40
     
3
37
3
48
     
4
35
4
17
  
  
    CLE
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
57
4
41
     
2
18
4
32
     
9
83
9
93
    
---
---
---
---
     
9
119
9
97
     
9
103
9
75
     
3
19
6
68
     
9
93
9
66
     
4
25
3
20
     
6
46
3
19
     
6
47
3
33
     
4
39
3
36
     
3
32
7
112
     
4
25
3
17
  
  
    DET
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
45
4
49
     
4
39
3
32
     
9
89
9
94
     
9
97
9
119
    
---
---
---
---
     
9
76
9
79
     
6
57
3
14
     
9
108
9
90
     
3
40
3
30
     
6
59
3
26
     
3
44
7
53
     
4
44
3
30
     
3
47
6
88
     
4
32
4
31
  
  
    KAN
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
4
31
4
47
     
3
27
4
38
     
9
95
9
95
     
9
75
9
103
     
9
79
9
76
    
---
---
---
---
     
3
25
2
13
     
9
67
9
64
     
3
18
7
73
     
3
31
6
54
     
7
51
2
23
     
4
29
4
38
     
6
59
3
37
     
3
22
4
27
  
  
    LAA
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
6
49
3
35
     
3
28
6
66
     
4
33
6
41
     
6
68
3
19
     
3
14
6
57
     
2
13
3
25
    
---
---
---
---
     
4
32
4
25
     
6
64
4
52
     
10
94
9
69
     
9
80
10
102
     
3
30
6
42
     
10
96
9
120
     
6
56
3
18
  
  
    MIN
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
25
3
42
     
4
47
3
35
     
9
86
10
114
     
9
66
9
93
     
9
90
9
108
     
9
64
9
67
     
4
25
4
32
    
---
---
---
---
     
7
66
3
32
     
3
24
7
65
     
3
44
6
64
     
2
21
4
45
     
7
77
3
39
     
3
24
3
30
  
  
    NYY
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
87
9
92
     
9
94
9
92
     
4
31
3
37
     
3
20
4
25
     
3
30
3
40
     
7
73
3
18
     
4
52
6
64
     
3
32
7
66
    
---
---
---
---
     
3
18
3
21
     
6
67
3
22
     
9
74
9
77
     
3
33
4
39
     
9
76
9
71
  
  
    OAK
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
20
2
19
     
7
48
3
24
     
3
27
6
35
     
3
19
6
46
     
3
26
6
59
     
6
54
3
31
     
9
69
10
94
     
7
65
3
24
     
3
21
3
18
    
---
---
---
---
     
9
64
10
88
     
6
49
3
20
     
10
97
9
104
     
3
19
7
61
  
  
    SEA
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
6
57
4
35
     
6
35
3
25
     
3
27
3
41
     
3
33
6
47
     
7
53
3
44
     
2
23
7
51
     
10
102
9
80
     
6
64
3
44
     
3
22
6
67
     
10
88
9
64
    
---
---
---
---
     
4
40
3
26
     
9
74
10
121
     
3
21
6
38
  
  
    TAM
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
104
9
91
     
9
75
9
79
     
7
40
3
32
     
3
36
4
39
     
3
30
4
44
     
4
38
4
29
     
6
42
3
30
     
4
45
2
21
     
9
77
9
74
     
3
20
6
49
     
3
26
4
40
    
---
---
---
---
     
3
36
6
55
     
9
66
9
62
  
  
    TEX
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
3
22
6
84
     
3
41
7
102
     
3
48
3
37
     
7
112
3
32
     
6
88
3
47
     
3
37
6
59
     
9
120
10
96
     
3
39
7
77
     
4
39
3
33
     
9
104
10
97
     
10
121
9
74
     
6
55
3
36
    
---
---
---
---
     
6
66
2
17
  
  
    TOR
   Games, home:
   Runs, home:
   Games, away:
   Runs, away:
     
9
97
9
81
     
9
85
9
66
     
4
17
4
35
     
3
17
4
25
     
4
31
4
32
     
4
27
3
22
     
3
18
6
56
     
3
30
3
24
     
9
71
9
76
     
7
61
3
19
     
6
38
3
21
     
9
62
9
66
     
2
17
6
66
    
---
---
---
---

First Calculations

From those data, we can easily make a first calculation of paired raw factors by simply making the per-teams-pair home and away runs-per-game ratios, then making a per-team-pair home-away runs factor:

Some Ratios

We can now strip away the scaffolding and show just the resultant per-team-pair home-away run ratios (we will assume that each park, relative to itself, is 1.000). That gives:

Normalizing Results

But notice something: each block of values was calculated using a particular park as the basis. Thus, the various factors calculated do not average to 1. To clarify: suppose that Park X is the worst park in the league for run scoring; in that case, every other park will necessarily, relative to Park X, show a runs factor above 1. But we can (if we assign Park X a value of 1 relative to itself) now calculate what the supposed "league-average" park looks like by taking the average of all the park runs factors (still, remember, relative to some particular park) and dividing each individual park factor by that average. In principle, we will now have determined what each park's runs "park factor" is relative to the desired (if imaginary) "league-average" ball park. The data now look like this (naturally, for each block, the average park factor is now almost exactly 1--any difference from exactly 1 being just cumulative rounding error):

A First Look at the Real Results

But at once, we see what a disaster we have on our hands. In principle, the factors shown in each block should all be the same. Very clearly, they are anything but. We can see that better if we rearrange the display of the data. Instead of blocking the data out by park used as basis, we block them out by supposed park factor calculated. That looks like this:


  
    Team | from
    ari
    atl
    chc
    cin
    col
    fla
    hou
    lad
    mil
    nym
    phi
    pit
    sdg
    sfo
    stl
    was
  
  
    ARI
    1.059
    1.363
    1.195
    0.615
    1.258
    1.438
    1.042
    1.153
    1.067
    0.933
    0.877
    1.036
    0.85
    0.921
    1.014
    1.086
  
  
    ATL
    0.821
    1.057
    1.242
    1.227
    1.359
    1.002
    1.006
    0.893
    1.142
    1.159
    0.658
    1.866
    0.769
    0.919
    0.799
    1.27
  
  
    CHC
    0.84
    0.807
    0.948
    0.985
    1.324
    0.978
    1.532
    0.477
    1.177
    0.655
    0.736
    0.698
    0.725
    0.951
    1.272
    2.184
  
  
    CIN
    1.792
    0.897
    1.002
    1.041
    0.826
    0.868
    1.563
    0.949
    0.914
    0.899
    1.556
    1.584
    0.706
    1.3
    0.757
    0.72
  
  
    COL
    0.883
    0.815
    0.751
    1.322
    1.048
    2.227
    0.739
    1.246
    0.722
    1.779
    0.863
    0.728
    1.232
    1.17
    1.685
    0.906
  
  
    FLA
    0.706
    1.012
    0.929
    1.15
    0.451
    0.958
    1.196
    1.274
    1.203
    1.082
    0.719
    0.912
    1.118
    1.413
    1.069
    0.819
  
  
    HOU
    1.059
    1.095
    0.645
    0.694
    1.477
    0.835
    1.042
    0.732
    1.216
    0.869
    1.415
    1.069
    1.765
    1.002
    1.165
    1.196
  
  
    LAD
    0.777
    1.001
    1.681
    0.928
    0.712
    0.637
    1.204
    0.846
    0.902
    0.947
    1.049
    0.77
    1.153
    0.828
    0.435
    0.536
  
  
    MIL
    0.895
    0.835
    0.727
    1.028
    1.31
    0.719
    0.773
    0.846
    0.902
    0.899
    0.638
    0.951
    0.692
    0.997
    1.158
    0.875
  
  
    NYM
    1.094
    0.879
    1.394
    1.117
    0.568
    0.853
    1.155
    0.861
    0.966
    0.964
    0.681
    1.617
    1.114
    0.646
    0.999
    1.043
  
  
    PHI
    1.067
    1.418
    1.138
    0.591
    1.073
    1.177
    0.65
    0.713
    1.249
    1.249
    0.883
    0.508
    1.127
    0.991
    0.397
    1.098
  
  
    PIT
    0.886
    0.491
    1.177
    0.57
    1.247
    0.911
    0.845
    0.952
    0.821
    0.516
    1.506
    0.866
    1.098
    0.861
    1.048
    0.906
  
  
    SDG
    0.958
    1.057
    1.005
    1.134
    0.654
    0.659
    0.454
    0.564
    1.002
    0.665
    0.602
    0.606
    0.769
    0.963
    0.721
    0.741
  
  
    SFO
    1.182
    1.182
    1.024
    0.823
    0.92
    0.697
    1.069
    1.051
    0.929
    1.533
    0.916
    1.034
    0.82
    1.028
    1.174
    0.887
  
  
    STL
    0.974
    1.233
    0.694
    1.282
    0.58
    0.836
    0.833
    1.814
    0.726
    0.899
    2.072
    0.77
    0.994
    0.816
    0.932
    0.699
  
  
    WAS
    1.006
    0.858
    0.448
    1.491
    1.193
    1.207
    0.898
    1.628
    1.063
    0.953
    0.83
    0.986
    1.069
    1.195
    1.375
    1.031
  




  
    Team | from
    bal
    bos
    chw
    cle
    det
    kan
    laa
    min
    nyy
    oak
    sea
    tam
    tex
    tor
  
  
    BAL
    1.071
    0.959
    1.285
    0.685
    0.913
    1.301
    1.333
    1.441
    1.068
    1.304
    0.807
    0.823
    1.969
    0.754
  
  
    BOS
    1.154
    1.033
    1.027
    0.846
    1.223
    0.906
    1.099
    0.852
    0.988
    1.068
    1.252
    0.991
    1.1
    0.701
  
  
    CHW
    0.883
    1.065
    1.059
    1.067
    1.181
    0.858
    0.773
    1.023
    1.607
    0.593
    1.331
    1.757
    0.795
    1.859
  
  
    CLE
    1.489
    1.162
    0.945
    0.952
    1.372
    1.178
    0.521
    1.208
    0.947
    1.108
    0.624
    0.765
    0.688
    0.996
  
  
    DET
    1.312
    0.944
    1.003
    0.776
    1.118
    0.826
    1.899
    1.029
    1.347
    1.038
    1.698
    1.035
    1.102
    0.932
  
  
    KAN
    0.707
    0.978
    1.059
    0.693
    1.162
    0.858
    1.196
    0.898
    0.581
    1.051
    0.555
    0.718
    0.822
    0.981
  
  
    LAA
    0.75
    0.876
    1.279
    1.704
    0.549
    0.669
    0.933
    1.098
    0.829
    1.122
    0.764
    1.344
    0.743
    1.404
  
  
    MIN
    0.638
    1.04
    0.888
    0.676
    0.932
    0.82
    0.729
    0.858
    0.893
    0.788
    1.205
    0.878
    0.873
    0.722
  
  
    NYY
    1.013
    1.055
    0.666
    1.015
    0.839
    1.491
    1.137
    0.97
    1.01
    0.784
    1.335
    0.904
    1.164
    0.966
  
  
    OAK
    0.752
    0.885
    1.634
    0.786
    0.986
    0.747
    0.761
    0.995
    1.178
    0.915
    0.708
    1.153
    0.866
    0.656
  
  
    SEA
    1.163
    0.723
    0.698
    1.337
    0.577
    1.354
    1.071
    0.624
    0.663
    1.132
    0.877
    1.086
    0.701
    0.998
  
  
    TAM
    1.224
    0.98
    0.567
    1.172
    1.017
    1.124
    0.653
    0.919
    1.051
    0.747
    0.76
    0.941
    1.35
    0.961
  
  
    TEX
    0.561
    0.969
    1.374
    1.428
    1.047
    1.076
    1.296
    1.014
    0.895
    1.09
    1.29
    0.719
    1.031
    1.168
  
  
    TOR
    1.283
    1.33
    0.515
    0.863
    1.083
    0.79
    0.6
    1.072
    0.943
    1.259
    0.793
    0.884
    0.797
    0.903

Examining the Disaster

To emphasize the comical size of the spreads, we can sort those data by factor size, to get:


  
    Team 
    park factor | (derived-from team)
  
  
    ARI
    0.615
(cin)
    0.85
(sdg)
    0.877
(phi)
    0.921
(sfo)
    0.933
(nym)
    1.014
(stl)
    1.036
(pit)
    1.042
(hou)
    1.057
(avg)
    1.059
(ari)
    1.067
(mil)
    1.086
(was)
    1.153
(lad)
    1.195
(chc)
    1.258
(col)
    1.363
(atl)
    1.438
(fla)
  
  
    ATL
    0.658
(phi)
    0.769
(sdg)
    0.799
(stl)
    0.821
(ari)
    0.893
(lad)
    0.919
(sfo)
    1.002
(fla)
    1.006
(hou)
    1.057
(atl)
    1.074
(avg)
    1.142
(mil)
    1.159
(nym)
    1.227
(cin)
    1.242
(chc)
    1.27
(was)
    1.359
(col)
    1.866
(pit)
  
  
    CHC
    0.477
(lad)
    0.655
(nym)
    0.698
(pit)
    0.725
(sdg)
    0.736
(phi)
    0.807
(atl)
    0.84
(ari)
    0.948
(chc)
    0.951
(sfo)
    0.978
(fla)
    0.985
(cin)
    1.018
(avg)
    1.177
(mil)
    1.272
(stl)
    1.324
(col)
    1.532
(hou)
    2.184
(was)
  
  
    CIN
    0.706
(sdg)
    0.72
(was)
    0.757
(stl)
    0.826
(col)
    0.868
(fla)
    0.897
(atl)
    0.899
(nym)
    0.914
(mil)
    0.949
(lad)
    1.002
(chc)
    1.041
(cin)
    1.086
(avg)
    1.3
(sfo)
    1.556
(phi)
    1.563
(hou)
    1.584
(pit)
    1.792
(ari)
  
  
    COL
    0.722
(mil)
    0.728
(pit)
    0.739
(hou)
    0.751
(chc)
    0.815
(atl)
    0.863
(phi)
    0.883
(ari)
    0.906
(was)
    1.048
(col)
    1.132
(avg)
    1.17
(sfo)
    1.232
(sdg)
    1.246
(lad)
    1.322
(cin)
    1.685
(stl)
    1.779
(nym)
    2.227
(fla)
  
  
    FLA
    0.451
(col)
    0.706
(ari)
    0.719
(phi)
    0.819
(was)
    0.912
(pit)
    0.929
(chc)
    0.958
(fla)
    1.001
(avg)
    1.012
(atl)
    1.069
(stl)
    1.082
(nym)
    1.118
(sdg)
    1.15
(cin)
    1.196
(hou)
    1.203
(mil)
    1.274
(lad)
    1.413
(sfo)
  
  
    HOU
    0.645
(chc)
    0.694
(cin)
    0.732
(lad)
    0.835
(fla)
    0.869
(nym)
    1.002
(sfo)
    1.042
(hou)
    1.059
(ari)
    1.069
(pit)
    1.08
(avg)
    1.095
(atl)
    1.165
(stl)
    1.196
(was)
    1.216
(mil)
    1.415
(phi)
    1.477
(col)
    1.765
(sdg)
  
  
    LAD
    0.435
(stl)
    0.536
(was)
    0.637
(fla)
    0.712
(col)
    0.77
(pit)
    0.777
(ari)
    0.828
(sfo)
    0.846
(lad)
    0.9
(avg)
    0.902
(mil)
    0.928
(cin)
    0.947
(nym)
    1.001
(atl)
    1.049
(phi)
    1.153
(sdg)
    1.204
(hou)
    1.681
(chc)
  
  
    MIL
    0.638
(phi)
    0.692
(sdg)
    0.719
(fla)
    0.727
(chc)
    0.773
(hou)
    0.835
(atl)
    0.846
(lad)
    0.875
(was)
    0.89
(avg)
    0.895
(ari)
    0.899
(nym)
    0.902
(mil)
    0.951
(pit)
    0.997
(sfo)
    1.028
(cin)
    1.158
(stl)
    1.31
(col)
  
  
    NYM
    0.568
(col)
    0.646
(sfo)
    0.681
(phi)
    0.853
(fla)
    0.861
(lad)
    0.879
(atl)
    0.964
(nym)
    0.966
(mil)
    0.997
(avg)
    0.999
(stl)
    1.043
(was)
    1.094
(ari)
    1.114
(sdg)
    1.117
(cin)
    1.155
(hou)
    1.394
(chc)
    1.617
(pit)
  
  
    PHI
    0.397
(stl)
    0.508
(pit)
    0.591
(cin)
    0.65
(hou)
    0.713
(lad)
    0.883
(phi)
    0.958
(avg)
    0.991
(sfo)
    1.067
(ari)
    1.073
(col)
    1.098
(was)
    1.127
(sdg)
    1.138
(chc)
    1.177
(fla)
    1.249
(nym)
    1.249
(mil)
    1.418
(atl)
  
  
    PIT
    0.491
(atl)
    0.516
(nym)
    0.57
(cin)
    0.821
(mil)
    0.845
(hou)
    0.861
(sfo)
    0.866
(pit)
    0.886
(ari)
    0.906
(was)
    0.911
(fla)
    0.919
(avg)
    0.952
(lad)
    1.048
(stl)
    1.098
(sdg)
    1.177
(chc)
    1.247
(col)
    1.506
(phi)
  
  
    SDG
    0.454
(hou)
    0.564
(lad)
    0.602
(phi)
    0.606
(pit)
    0.654
(col)
    0.659
(fla)
    0.665
(nym)
    0.721
(stl)
    0.741
(was)
    0.769
(sdg)
    0.785
(avg)
    0.958
(ari)
    0.963
(sfo)
    1.002
(mil)
    1.005
(chc)
    1.057
(atl)
    1.134
(cin)
  
  
    SFO
    0.697
(fla)
    0.82
(sdg)
    0.823
(cin)
    0.887
(was)
    0.916
(phi)
    0.92
(col)
    0.929
(mil)
    1.017
(avg)
    1.024
(chc)
    1.028
(sfo)
    1.034
(pit)
    1.051
(lad)
    1.069
(hou)
    1.174
(stl)
    1.182
(ari)
    1.182
(atl)
    1.533
(nym)
  
  
    STL
    0.58
(col)
    0.694
(chc)
    0.699
(was)
    0.726
(mil)
    0.77
(pit)
    0.816
(sfo)
    0.833
(hou)
    0.836
(fla)
    0.899
(nym)
    0.932
(stl)
    0.974
(ari)
    0.994
(sdg)
    1.009
(avg)
    1.233
(atl)
    1.282
(cin)
    1.814
(lad)
    2.072
(phi)
  
  
    WAS
    0.448
(chc)
    0.83
(phi)
    0.858
(atl)
    0.898
(hou)
    0.953
(nym)
    0.986
(pit)
    1.006
(ari)
    1.031
(was)
    1.063
(mil)
    1.069
(sdg)
    1.077
(avg)
    1.193
(col)
    1.195
(sfo)
    1.207
(fla)
    1.375
(stl)
    1.491
(cin)
    1.628
(lad)
  




  
    Team 
    park factor | (derived-from team)
  
  
    BAL
    0.685
(cle)
    0.754
(tor)
    0.807
(sea)
    0.823
(tam)
    0.913
(det)
    0.959
(bos)
    1.068
(nyy)
    1.071
(bal)
    1.122
(avg)
    1.285
(chw)
    1.301
(kan)
    1.304
(oak)
    1.333
(laa)
    1.441
(min)
    1.969
(tex)
  
  
    BOS
    0.701
(tor)
    0.846
(cle)
    0.852
(min)
    0.906
(kan)
    0.988
(nyy)
    0.991
(tam)
    1.017
(avg)
    1.027
(chw)
    1.033
(bos)
    1.068
(oak)
    1.099
(laa)
    1.1
(tex)
    1.154
(bal)
    1.223
(det)
    1.252
(sea)
  
  
    CHW
    0.593
(oak)
    0.773
(laa)
    0.795
(tex)
    0.858
(kan)
    0.883
(bal)
    1.023
(min)
    1.059
(chw)
    1.065
(bos)
    1.067
(cle)
    1.132
(avg)
    1.181
(det)
    1.331
(sea)
    1.607
(nyy)
    1.757
(tam)
    1.859
(tor)
  
  
    CLE
    0.521
(laa)
    0.624
(sea)
    0.688
(tex)
    0.765
(tam)
    0.945
(chw)
    0.947
(nyy)
    0.952
(cle)
    0.996
(tor)
    0.997
(avg)
    1.108
(oak)
    1.162
(bos)
    1.178
(kan)
    1.208
(min)
    1.372
(det)
    1.489
(bal)
  
  
    DET
    0.776
(cle)
    0.826
(kan)
    0.932
(tor)
    0.944
(bos)
    1.003
(chw)
    1.029
(min)
    1.035
(tam)
    1.038
(oak)
    1.102
(tex)
    1.118
(det)
    1.147
(avg)
    1.312
(bal)
    1.347
(nyy)
    1.698
(sea)
    1.899
(laa)
  
  
    KAN
    0.555
(sea)
    0.581
(nyy)
    0.693
(cle)
    0.707
(bal)
    0.718
(tam)
    0.822
(tex)
    0.858
(kan)
    0.876
(avg)
    0.898
(min)
    0.978
(bos)
    0.981
(tor)
    1.051
(oak)
    1.059
(chw)
    1.162
(det)
    1.196
(laa)
  
  
    LAA
    0.549
(det)
    0.669
(kan)
    0.743
(tex)
    0.75
(bal)
    0.764
(sea)
    0.829
(nyy)
    0.876
(bos)
    0.933
(laa)
    1.005
(avg)
    1.098
(min)
    1.122
(oak)
    1.279
(chw)
    1.344
(tam)
    1.404
(tor)
    1.704
(cle)
  
  
    MIN
    0.638
(bal)
    0.676
(cle)
    0.722
(tor)
    0.729
(laa)
    0.788
(oak)
    0.82
(kan)
    0.853
(avg)
    0.858
(min)
    0.873
(tex)
    0.878
(tam)
    0.888
(chw)
    0.893
(nyy)
    0.932
(det)
    1.04
(bos)
    1.205
(sea)
  
  
    NYY
    0.666
(chw)
    0.784
(oak)
    0.839
(det)
    0.904
(tam)
    0.966
(tor)
    0.97
(min)
    1.01
(nyy)
    1.013
(bal)
    1.015
(cle)
    1.025
(avg)
    1.055
(bos)
    1.137
(laa)
    1.164
(tex)
    1.335
(sea)
    1.491
(kan)
  
  
    OAK
    0.656
(tor)
    0.708
(sea)
    0.747
(kan)
    0.752
(bal)
    0.761
(laa)
    0.786
(cle)
    0.866
(tex)
    0.885
(bos)
    0.915
(oak)
    0.93
(avg)
    0.986
(det)
    0.995
(min)
    1.153
(tam)
    1.178
(nyy)
    1.634
(chw)
  
  
    SEA
    0.577
(det)
    0.624
(min)
    0.663
(nyy)
    0.698
(chw)
    0.701
(tex)
    0.723
(bos)
    0.877
(sea)
    0.929
(avg)
    0.998
(tor)
    1.071
(laa)
    1.086
(tam)
    1.132
(oak)
    1.163
(bal)
    1.337
(cle)
    1.354
(kan)
  
  
    TAM
    0.567
(chw)
    0.653
(laa)
    0.747
(oak)
    0.76
(sea)
    0.919
(min)
    0.941
(tam)
    0.961
(tor)
    0.962
(avg)
    0.98
(bos)
    1.017
(det)
    1.051
(nyy)
    1.124
(kan)
    1.172
(cle)
    1.224
(bal)
    1.35
(tex)
  
  
    TEX
    0.561
(bal)
    0.719
(tam)
    0.895
(nyy)
    0.969
(bos)
    1.014
(min)
    1.031
(tex)
    1.047
(det)
    1.068
(avg)
    1.076
(kan)
    1.09
(oak)
    1.168
(tor)
    1.29
(sea)
    1.296
(laa)
    1.374
(chw)
    1.428
(cle)
  
  
    TOR
    0.515
(chw)
    0.6
(laa)
    0.79
(kan)
    0.793
(sea)
    0.797
(tex)
    0.863
(cle)
    0.884
(tam)
    0.903
(tor)
    0.937
(avg)
    0.943
(nyy)
    1.072
(min)
    1.083
(det)
    1.259
(oak)
    1.283
(bal)
    1.33
(bos)

Hiding Behind Averages

Let me repeat: if this method worked in practice, for each park the runs "park factor" calculated from other parks should be nearly the same: every horizontal line in the Table above should have nearly identical numbers right across. But in reality, we see spreads approaching a 3:1 ratio. That has nothing to do with the methodology: it is entirely a result of ridiculously small data samples--which is why calculating "park factors" is a bad joke.

In the usual figuring presented to the public, that is all pretty well hidden, because what you get for a given park is--more or less--an averaging of the sorts of results here broken out in detail. You can disguise (though not correct) an awful lot of sins in data analysis by taking averages. (A prediction that every team in baseball will finish with a .500 record will not look bad at all if one takes some Standard Error calculations of the actual-versus-predicted results.)

If you want to see what averaging can hide, here is a tabulation of the averaged runs "park factors" for 2008; for comparison, I show the ESPN results as well (not to pick on ESPN--it's just that the method they use is typical). The "best" column means best-guess, which is what all our figuring above amounts to. I have included a "delta" (differences) column, both as a ratio and as a percentage. What you will notice is that in a very broad way, there is agreement: San Diego seems to have, without much doubt, the stingiest stadium in the majors, and the general pattern from stingiest to most generous crudely corresponds.



  
    Team
    Best
Guess
    Typical
(ESPN)
    Typical/Best
    Typical/Best
% difference
  
  
  
    SDG
    0.785
    0.796
    1.014
    + 1.4
  

  
    MIL
    0.890
    0.945
    1.062
    + 6.2
  

  
    LAD
    0.900
    0.842
    0.936
    - 6.4
  

  
    PIT
    0.919
    0.898
    0.977
    - 2.3
  

  
    PHI
    0.958
    1.029
    1.074
    + 7.4
  

  
    NYM
    0.997
    0.946
    0.949
    - 5.1
  

  
    FLA
    1.001
    0.954
    0.953
    - 4.7
  

  
    STL
    1.009
    0.943
    0.935
    - 6.5
  

  
    SFO
    1.017
    1.045
    1.028
    + 2.8
  

  
    CHC
    1.018
    1.068
    1.049
    + 4.9
  

  
    ARI
    1.057
    1.135
    1.074
    + 7.4
  

  
    ATL
    1.074
    1.063
    0.990
    - 1.0
  

  
    WAS
    1.077
    1.038
    0.964
    - 3.6
  

  
    HOU
    1.080
    1.036
    0.959
    - 4.1
  

  
    CIN
    1.086
    1.069
    0.984
    - 1.6
  

  
    COL
    1.132
    1.126
    0.995
    - 0.5
  

  
    avg
    1.000
    0.996
    1.000 = league average
  



  
    MIN
    0.853
    0.887
    1.040
    + 4.0
  

  
    KAN
    0.876
    0.929
    1.061
    + 6.1
  

  
    SEA
    0.929
    0.932
    1.003
    + 0.3
  

  
    OAK
    0.930
    0.916
    0.985
    - 1.5
  

  
    TOR
    0.937
    0.959
    1.023
    + 2.3
  

  
    TAM
    0.962
    0.955
    0.993
    - 0.7
  

  
    CLE
    0.997
    0.995
    0.998
    - 0.2
  

  
    LAA
    1.005
    1.017
    1.012
    + 1.2
  

  
    BOS
    1.017
    1.077
    1.059
    + 5.9
  

  
    NYY
    1.025
    1.040
    1.015
    + 1.5
  

  
    TEX
    1.068
    1.142
    1.069
    + 6.9
  

  
    BAL
    1.122
    1.051
    0.937
    - 6.3
  

  
    CHW
    1.132
    1.122
    0.991
    - 0.9
  

  
    DET
    1.147
    1.077
    0.939
    - 6.1
  

  
    avg
    1.000
    1.007
    1.000 = league average

But the point here is not whose method is more accurate--when you average the results calculated here, all you're doing is making a slightly better approximation of what the "typical" method achieves, so of course they sort of agree. The real point is that none of them are really much good save in a very general qualitative, not quantitative, way. We can say, for example, that Colorado's park boosts run scoring substantially--but if we try to actually adjust data to correctly allow for it, we're just going to be faking it.

The Bottom Line

The only way one could hope for better results is to cumulate data over several seasons. But, as we already noted, the frequency of structural changes--not to mention actual park replacements--and even such things as percentage of times a park with a retractable roof has it open in a given season, makes any such technique yet another disguising of error by averaging.

Bottom line: if MLB were to stabilize stadia--say, no structural changes any more often than every three years--and cut out interleague play (a folly in any event), we might in time get more meaningful data. But none of that is going to happen, so we need to accept that in analysis the best we can do is what is done on this site: calculate measures from exact data and let the viewer apply a rough mental adjustment to results. Anything else is the sort of thing meant by "lies, damned lies, and statistics."

(Just as food for thought: in the last 10 years alone--2000 through 2009, inclusive--fully a dozen wholly new ballparks debuted, an average of more than one a year. Meanwhile, those with patience and a lot of time on their hands could make a list of structural changes to existing parks during that period, or any other that strikes one's fancy; possible starting places for such eager beavers would include the Clem's Baseball stadium chronology page; or the Baseball Parks park-changes pages.)

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