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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:

Team | vs. ari atl chc cin col fla hou lad mil nym phi pit sdg sfo stl was
ARI
   h R/G:
   a R/G:
   ratio:

-----
-----
-------
 
12.25
9.5
0.776
 
9.667
7.667
0.793
 
4.333
7.333
1.692
 
10.667
8.889
0.833
 
8
5.333
0.667
 
11
11
1
 
10.444
7.667
0.734
 
10.25
8.667
0.846
 
10
10.333
1.033
 
11.25
11.333
1.007
 
8.667
7.25
0.837
 
9.333
8.444
0.905
 
7.667
8.556
1.116
 
10.333
9.5
0.919
 
6.667
6.333
0.95
ATL
   h R/G:
   a R/G:
   ratio:
 
9.5
12.25
1.289

-----
-----
-------
 
12.667
9.667
0.763
 
11
9.333
0.848
 
11.667
9
0.771
 
10.333
9.889
0.957
 
9.333
9.667
1.036
 
6.333
6
0.947
 
6.333
5
0.789
 
9.889
8.222
0.831
 
8.778
11.778
1.342
 
14
6.5
0.464
 
8
8
1
 
7.75
8.667
1.118
 
12
14
1.167
 
11.222
9.111
0.812
CHC
   h R/G:
   a R/G:
   ratio:
 
7.667
9.667
1.261
 
9.667
12.667
1.31

-----
-----
-------
 
9.778
10.333
1.057
 
12
9.5
0.792
 
8.5
8.333
0.98
 
9.556
6.5
0.68
 
3.667
6.5
1.773
 
11.556
8.857
0.766
 
8.5
12.5
1.471
 
7.5
9
1.2
 
10.111
12.556
1.242
 
9.75
10.333
1.06
 
8.333
9
1.08
 
10.167
7.444
0.732
 
12
5.667
0.472
CIN
   h R/G:
   a R/G:
   ratio:
 
7.333
4.333
0.591
 
9.333
11
1.179
 
10.333
9.778
0.946

-----
-----
-------
 
8.667
11
1.269
 
12
13.25
1.104
 
11
7.333
0.667
 
8.6
7.667
0.891
 
8.667
8.556
0.987
 
11.5
12.333
1.072
 
9.25
5.25
0.568
 
10.667
5.833
0.547
 
10.333
11.25
1.089
 
14.333
11.333
0.791
 
8.667
10.667
1.231
 
6.75
9.667
1.432
COL
   h R/G:
   a R/G:
   ratio:
 
8.889
10.667
1.2
 
9
11.667
1.296
 
9.5
12
1.263
 
11
8.667
0.788

-----
-----
-------
 
19.75
8.5
0.43
 
7.333
10.333
1.409
 
11.778
8
0.679
 
8
10
1.25
 
8
4.333
0.542
 
14
14.333
1.024
 
9.25
11
1.189
 
12.111
7.556
0.624
 
9.111
8
0.878
 
10.25
5.667
0.553
 
10.25
11.667
1.138
FLA
   h R/G:
   a R/G:
   ratio:
 
5.333
8
1.5
 
9.889
10.333
1.045
 
8.333
8.5
1.02
 
13.25
12
0.906
 
8.5
19.75
2.324

-----
-----
-------
 
10.333
9
0.871
 
11.667
7.75
0.664
 
6.667
5
0.75
 
9.111
8.111
0.89
 
8.778
10.778
1.228
 
10
9.5
0.95
 
10.667
7.333
0.688
 
11
8
0.727
 
6.5
5.667
0.872
 
9.333
11.75
1.259
HOU
   h R/G:
   a R/G:
   ratio:
 
11
11
1
 
9.667
9.333
0.966
 
6.5
9.556
1.47
 
7.333
11
1.5
 
10.333
7.333
0.71
 
9
10.333
1.148

-----
-----
-------
 
7.5
8.667
1.156
 
11.833
8.778
0.742
 
7.667
8.5
1.109
 
11.75
7.333
0.624
 
10.143
8.222
0.811
 
15.5
6.75
0.435
 
9.75
10
1.026
 
8.333
6.667
0.8
 
9.667
8.333
0.862
LAD
   h R/G:
   a R/G:
   ratio:
 
7.667
10.444
1.362
 
6
6.333
1.056
 
6.5
3.667
0.564
 
7.667
8.6
1.122
 
8
11.778
1.472
 
7.75
11.667
1.505
 
8.667
7.5
0.865

-----
-----
-------
 
9
9
1
 
9.333
9.5
1.018
 
9.5
8
0.842
 
10.667
12
1.125
 
10.333
6.889
0.667
 
6.444
8
1.241
 
4.667
10
2.143
 
4.333
8.333
1.923
MIL
   h R/G:
   a R/G:
   ratio:
 
8.667
10.25
1.183
 
5
6.333
1.267
 
8.857
11.556
1.305
 
8.556
8.667
1.013
 
10
8
0.8
 
5
6.667
1.333
 
8.778
11.833
1.348
 
9
9
1

-----
-----
-------
 
9.333
10
1.071
 
6.5
9
1.385
 
9.333
8.5
0.911
 
6
6.667
1.111
 
11
11.333
1.03
 
9.667
7.778
0.805
 
7
8.25
1.179
NYM
   h R/G:
   a R/G:
   ratio:
 
10.333
10
0.968
 
8.222
9.889
1.203
 
12.5
8.5
0.68
 
12.333
11.5
0.932
 
4.333
8
1.846
 
8.111
9.111
1.123
 
8.5
7.667
0.902
 
9.5
9.333
0.982
 
10
9.333
0.933

-----
-----
-------
 
7.889
10.222
1.296
 
11.667
6.25
0.536
 
8.333
5.75
0.69
 
7.333
11.667
1.591
 
12.333
11.5
0.932
 
10.111
10
0.989
PHI
   h R/G:
   a R/G:
   ratio:
 
11.333
11.25
0.993
 
11.778
8.778
0.745
 
9
7.5
0.833
 
5.25
9.25
1.762
 
14.333
14
0.977
 
10.778
8.778
0.814
 
7.333
11.75
1.602
 
8
9.5
1.188
 
9
6.5
0.722
 
10.222
7.889
0.772

-----
-----
-------
 
5.667
9.667
1.706
 
7.333
5
0.682
 
9
9.333
1.037
 
4.333
10.167
2.346
 
9.222
8.667
0.94
PIT
   h R/G:
   a R/G:
   ratio:
 
7.25
8.667
1.195
 
6.5
14
2.154
 
12.556
10.111
0.805
 
5.833
10.667
1.829
 
11
9.25
0.841
 
9.5
10
1.053
 
8.222
10.143
1.234
 
12
10.667
0.889
 
8.5
9.333
1.098
 
6.25
11.667
1.867
 
9.667
5.667
0.586

-----
-----
-------
 
10
7
0.7
 
10.333
12.333
1.194
 
12.375
11
0.889
 
9.667
11
1.138
SDG
   h R/G:
   a R/G:
   ratio:
 
8.444
9.333
1.105
 
8
8
1
 
10.333
9.75
0.944
 
11.25
10.333
0.919
 
7.556
12.111
1.603
 
7.333
10.667
1.455
 
6.75
15.5
2.296
 
6.889
10.333
1.5
 
6.667
6
0.9
 
5.75
8.333
1.449
 
5
7.333
1.467
 
7
10
1.429

-----
-----
-------
 
6.667
7.111
1.067
 
9.667
12.5
1.293
 
7.667
10.667
1.391
SFO
   h R/G:
   a R/G:
   ratio:
 
8.556
7.667
0.896
 
8.667
7.75
0.894
 
9
8.333
0.926
 
11.333
14.333
1.265
 
8
9.111
1.139
 
8
11
1.375
 
10
9.75
0.975
 
8
6.444
0.806
 
11.333
11
0.971
 
11.667
7.333
0.629
 
9.333
9
0.964
 
12.333
10.333
0.838
 
7.111
6.667
0.938

-----
-----
-------
 
10.5
8.333
0.794
 
6.667
7.75
1.163
STL
   h R/G:
   a R/G:
   ratio:
 
9.5
10.333
1.088
 
14
12
0.857
 
7.444
10.167
1.366
 
10.667
8.667
0.813
 
5.667
10.25
1.809
 
5.667
6.5
1.147
 
6.667
8.333
1.25
 
10
4.667
0.467
 
7.778
9.667
1.243
 
11.5
12.333
1.072
 
10.167
4.333
0.426
 
11
12.375
1.125
 
12.5
9.667
0.773
 
8.333
10.5
1.26

-----
-----
-------
 
7
10.333
1.476
WAS
   h R/G:
   a R/G:
   ratio:
 
6.333
6.667
1.053
 
9.111
11.222
1.232
 
5.667
12
2.118
 
9.667
6.75
0.698
 
11.667
10.25
0.879
 
11.75
9.333
0.794
 
8.333
9.667
1.16
 
8.333
4.333
0.52
 
8.25
7
0.848
 
10
10.111
1.011
 
8.667
9.222
1.064
 
11
9.667
0.879
 
10.667
7.667
0.719
 
7.75
6.667
0.86
 
10.333
7
0.677

-----
-----
-------

Team | vs. bal bos chw cle det kan laa min nyy oak sea tam tex tor
BAL
   h R/G:
   a R/G:
   ratio:

-----
-----
-------
 
10.111
10.889
1.077
 
9.4
7.75
0.824
 
10.25
14.25
1.39
 
12.25
15
1.224
 
11.75
7.75
0.66
 
11.667
8.167
0.7
 
14
8.333
0.595
 
10.222
9.667
0.946
 
9.5
6.667
0.702
 
8.75
9.5
1.086
 
10.111
11.556
1.143
 
14
7.333
0.524
 
9
10.778
1.198
BOS
   h R/G:
   a R/G:
   ratio:
 
10.889
10.111
0.929

-----
-----
-------
 
8
8.25
1.031
 
8
9
1.125
 
10.667
9.75
0.914
 
9.5
9
0.947
 
11
9.333
0.848
 
11.667
11.75
1.007
 
10.222
10.444
1.022
 
8
6.857
0.857
 
8.333
5.833
0.7
 
8.778
8.333
0.949
 
14.571
13.667
0.938
 
7.333
9.444
1.288
CHW
   h R/G:
   a R/G:
   ratio:
 
7.75
9.4
1.213
 
8.25
8
0.97

-----
-----
-------
 
10.333
9.222
0.892
 
10.444
9.889
0.947
 
10.556
10.556
1
 
6.833
8.25
1.207
 
11.4
9.556
0.838
 
12.333
7.75
0.628
 
5.833
9
1.543
 
13.667
9
0.659
 
10.667
5.714
0.536
 
12.333
16
1.297
 
8.75
4.25
0.486
CLE
   h R/G:
   a R/G:
   ratio:
 
14.25
10.25
0.719
 
9
8
0.889
 
9.222
10.333
1.12

-----
-----
-------
 
13.222
10.778
0.815
 
11.444
8.333
0.728
 
6.333
11.333
1.789
 
10.333
7.333
0.71
 
6.25
6.667
1.067
 
7.667
6.333
0.826
 
7.833
11
1.404
 
9.75
12
1.231
 
10.667
16
1.5
 
6.25
5.667
0.907
DET
   h R/G:
   a R/G:
   ratio:
 
15
12.25
0.817
 
9.75
10.667
1.094
 
9.889
10.444
1.056
 
10.778
13.222
1.227

-----
-----
-------
 
8.444
8.778
1.039
 
9.5
4.667
0.491
 
12
10
0.833
 
13.333
10
0.75
 
9.833
8.667
0.881
 
14.667
7.571
0.516
 
11
10
0.909
 
15.667
14.667
0.936
 
8
7.75
0.969
KAN
   h R/G:
   a R/G:
   ratio:
 
7.75
11.75
1.516
 
9
9.5
1.056
 
10.556
10.556
1
 
8.333
11.444
1.373
 
8.778
8.444
0.962

-----
-----
-------
 
8.333
6.5
0.78
 
7.444
7.111
0.955
 
6
10.429
1.738
 
10.333
9
0.871
 
7.286
11.5
1.578
 
7.25
9.5
1.31
 
9.833
12.333
1.254
 
7.333
6.75
0.92
LAA
   h R/G:
   a R/G:
   ratio:
 
8.167
11.667
1.429
 
9.333
11
1.179
 
8.25
6.833
0.828
 
11.333
6.333
0.559
 
4.667
9.5
2.036
 
6.5
8.333
1.282

-----
-----
-------
 
8
6.25
0.781
 
10.667
13
1.219
 
9.4
7.667
0.816
 
8.889
10.2
1.148
 
10
7
0.7
 
9.6
13.333
1.389
 
9.333
6
0.643
MIN
   h R/G:
   a R/G:
   ratio:
 
8.333
14
1.68
 
11.75
11.667
0.993
 
9.556
11.4
1.193
 
7.333
10.333
1.409
 
10
12
1.2
 
7.111
7.444
1.047
 
6.25
8
1.28

-----
-----
-------
 
9.429
10.667
1.131
 
8
9.286
1.161
 
14.667
10.667
0.727
 
10.5
11.25
1.071
 
11
13
1.182
 
8
10
1.25
NYY
   h R/G:
   a R/G:
   ratio:
 
9.667
10.222
1.057
 
10.444
10.222
0.979
 
7.75
12.333
1.591
 
6.667
6.25
0.938
 
10
13.333
1.333
 
10.429
6
0.575
 
13
10.667
0.821
 
10.667
9.429
0.884

-----
-----
-------
 
6
7
1.167
 
11.167
7.333
0.657
 
8.222
8.556
1.041
 
11
9.75
0.886
 
8.444
7.889
0.934
OAK
   h R/G:
   a R/G:
   ratio:
 
6.667
9.5
1.425
 
6.857
8
1.167
 
9
5.833
0.648
 
6.333
7.667
1.211
 
8.667
9.833
1.135
 
9
10.333
1.148
 
7.667
9.4
1.226
 
9.286
8
0.862
 
7
6
0.857

-----
-----
-------
 
7.111
8.8
1.238
 
8.167
6.667
0.816
 
9.7
11.556
1.191
 
6.333
8.714
1.376
SEA
   h R/G:
   a R/G:
   ratio:
 
9.5
8.75
0.921
 
5.833
8.333
1.429
 
9
13.667
1.519
 
11
7.833
0.712
 
7.571
14.667
1.937
 
11.5
7.286
0.634
 
10.2
8.889
0.871
 
10.667
14.667
1.375
 
7.333
11.167
1.523
 
8.8
7.111
0.808

-----
-----
-------
 
10
8.667
0.867
 
8.222
12.1
1.472
 
7
6.333
0.905
TAM
   h R/G:
   a R/G:
   ratio:
 
11.556
10.111
0.875
 
8.333
8.778
1.053
 
5.714
10.667
1.867
 
12
9.75
0.813
 
10
11
1.1
 
9.5
7.25
0.763
 
7
10
1.429
 
11.25
10.5
0.933
 
8.556
8.222
0.961
 
6.667
8.167
1.225
 
8.667
10
1.154

-----
-----
-------
 
12
9.167
0.764
 
7.333
6.889
0.939
TEX
   h R/G:
   a R/G:
   ratio:
 
7.333
14
1.909
 
13.667
14.571
1.066
 
16
12.333
0.771
 
16
10.667
0.667
 
14.667
15.667
1.068
 
12.333
9.833
0.797
 
13.333
9.6
0.72
 
13
11
0.846
 
9.75
11
1.128
 
11.556
9.7
0.839
 
12.1
8.222
0.68
 
9.167
12
1.309

-----
-----
-------
 
11
8.5
0.773
TOR
   h R/G:
   a R/G:
   ratio:
 
10.778
9
0.835
 
9.444
7.333
0.776
 
4.25
8.75
2.059
 
5.667
6.25
1.103
 
7.75
8
1.032
 
6.75
7.333
1.086
 
6
9.333
1.556
 
10
8
0.8
 
7.889
8.444
1.07
 
8.714
6.333
0.727
 
6.333
7
1.105
 
6.889
7.333
1.065
 
8.5
11
1.294

-----
-----
-------

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:

Team | vs. ari atl chc cin col fla hou lad mil nym phi pit sdg sfo stl was avg
ARI 1 0.776 0.793 1.692 0.833 0.667 1 0.734 0.846 1.033 1.007 0.837 0.905 1.116 0.919 0.95 0.944
ATL 1.289 1 0.763 0.848 0.771 0.957 1.036 0.947 0.789 0.831 1.342 0.464 1 1.118 1.167 0.812 0.946
CHC 1.261 1.31 1 1.057 0.792 0.98 0.68 1.773 0.766 1.471 1.2 1.242 1.06 1.08 0.732 0.472 1.055
CIN 0.591 1.179 0.946 1 1.269 1.104 0.667 0.891 0.987 1.072 0.568 0.547 1.089 0.791 1.231 1.432 0.96
COL 1.2 1.296 1.263 0.788 1 0.43 1.409 0.679 1.25 0.542 1.024 1.189 0.624 0.878 0.553 1.138 0.954
FLA 1.5 1.045 1.02 0.906 2.324 1 0.871 0.664 0.75 0.89 1.228 0.95 0.688 0.727 0.872 1.259 1.043
HOU 1 0.966 1.47 1.5 0.71 1.148 1 1.156 0.742 1.109 0.624 0.811 0.435 1.026 0.8 0.862 0.96
LAD 1.362 1.056 0.564 1.122 1.472 1.505 0.865 1 1 1.018 0.842 1.125 0.667 1.241 2.143 1.923 1.182
MIL 1.183 1.267 1.305 1.013 0.8 1.333 1.348 1 1 1.071 1.385 0.911 1.111 1.03 0.805 1.179 1.109
NYM 0.968 1.203 0.68 0.932 1.846 1.123 0.902 0.982 0.933 1 1.296 0.536 0.69 1.591 0.932 0.989 1.038
PHI 0.993 0.745 0.833 1.762 0.977 0.814 1.602 1.188 0.722 0.772 1 1.706 0.682 1.037 2.346 0.94 1.132
PIT 1.195 2.154 0.805 1.829 0.841 1.053 1.234 0.889 1.098 1.867 0.586 1 0.7 1.194 0.889 1.138 1.154
SDG 1.105 1 0.944 0.919 1.603 1.455 2.296 1.5 0.9 1.449 1.467 1.429 1 1.067 1.293 1.391 1.301
SFO 0.896 0.894 0.926 1.265 1.139 1.375 0.975 0.806 0.971 0.629 0.964 0.838 0.938 1 0.794 1.163 0.973
STL 1.088 0.857 1.366 0.813 1.809 1.147 1.25 0.467 1.243 1.072 0.426 1.125 0.773 1.26 1 1.476 1.073
WAS 1.053 1.232 2.118 0.698 0.879 0.794 1.16 0.52 0.848 1.011 1.064 0.879 0.719 0.86 0.677 1 0.97

Team | vs. bal bos chw cle det kan laa min nyy oak sea tam tex tor avg
BAL 1 1.077 0.824 1.39 1.224 0.66 0.7 0.595 0.946 0.702 1.086 1.143 0.524 1.198 0.933
BOS 0.929 1 1.031 1.125 0.914 0.947 0.848 1.007 1.022 0.857 0.7 0.949 0.938 1.288 0.968
CHW 1.213 0.97 1 0.892 0.947 1 1.207 0.838 0.628 1.543 0.659 0.536 1.297 0.486 0.944
CLE 0.719 0.889 1.12 1 0.815 0.728 1.789 0.71 1.067 0.826 1.404 1.231 1.5 0.907 1.05
DET 0.817 1.094 1.056 1.227 1 1.039 0.491 0.833 0.75 0.881 0.516 0.909 0.936 0.969 0.894
KAN 1.516 1.056 1 1.373 0.962 1 0.78 0.955 1.738 0.871 1.578 1.31 1.254 0.92 1.165
LAA 1.429 1.179 0.828 0.559 2.036 1.282 1 0.781 1.219 0.816 1.148 0.7 1.389 0.643 1.072
MIN 1.68 0.993 1.193 1.409 1.2 1.047 1.28 1 1.131 1.161 0.727 1.071 1.182 1.25 1.166
NYY 1.057 0.979 1.591 0.938 1.333 0.575 0.821 0.884 1 1.167 0.657 1.041 0.886 0.934 0.99
OAK 1.425 1.167 0.648 1.211 1.135 1.148 1.226 0.862 0.857 1 1.238 0.816 1.191 1.376 1.093
SEA 0.921 1.429 1.519 0.712 1.937 0.634 0.871 1.375 1.523 0.808 1 0.867 1.472 0.905 1.141
TAM 0.875 1.053 1.867 0.813 1.1 0.763 1.429 0.933 0.961 1.225 1.154 1 0.764 0.939 1.063
TEX 1.909 1.066 0.771 0.667 1.068 0.797 0.72 0.846 1.128 0.839 0.68 1.309 1 0.773 0.97
TOR 0.835 0.776 2.059 1.103 1.032 1.086 1.556 0.8 1.07 0.727 1.105 1.065 1.294 1 1.108

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):

Team | vs. ari atl chc cin col fla hou lad mil nym phi pit sdg sfo stl was avg
ARI 1.059 0.821 0.84 1.792 0.883 0.706 1.059 0.777 0.895 1.094 1.067 0.886 0.958 1.182 0.974 1.006 0.996
ATL 1.363 1.057 0.807 0.897 0.815 1.012 1.095 1.001 0.835 0.879 1.418 0.491 1.057 1.182 1.233 0.858 0.996
CHC 1.195 1.242 0.948 1.002 0.751 0.929 0.645 1.681 0.727 1.394 1.138 1.177 1.005 1.024 0.694 0.448 1.003
CIN 0.615 1.227 0.985 1.041 1.322 1.15 0.694 0.928 1.028 1.117 0.591 0.57 1.134 0.823 1.282 1.491 0.997
COL 1.258 1.359 1.324 0.826 1.048 0.451 1.477 0.712 1.31 0.568 1.073 1.247 0.654 0.92 0.58 1.193 0.997
FLA 1.438 1.002 0.978 0.868 2.227 0.958 0.835 0.637 0.719 0.853 1.177 0.911 0.659 0.697 0.836 1.207 1.003
HOU 1.042 1.006 1.532 1.563 0.739 1.196 1.042 1.204 0.773 1.155 0.65 0.845 0.454 1.069 0.833 0.898 0.997
LAD 0.893 0.477 0.949 1.246 1.274 0.732 0.846 0.846 0.861 0.713 0.952 0.564 1.051 1.814 1.628 0 1.153
MIL 1.067 1.142 1.177 0.914 0.722 1.203 1.216 0.902 0.902 0.966 1.249 0.821 1.002 0.929 0.726 1.063 1.007
NYM 0.933 1.159 0.655 0.899 1.779 1.082 0.869 0.947 0.899 0.964 1.249 0.516 0.665 1.533 0.899 0.953 1.002
PHI 0.877 0.658 0.736 1.556 0.863 0.719 1.415 1.049 0.638 0.681 0.883 1.506 0.602 0.916 2.072 0.83 1.008
PIT 1.036 1.866 0.698 1.584 0.728 0.912 1.069 0.77 0.951 1.617 0.508 0.866 0.606 1.034 0.77 0.986 1.009
SDG 0.85 0.769 0.725 0.706 1.232 1.118 1.765 1.153 0.692 1.114 1.127 1.098 0.769 0.82 0.994 1.069 1.015
SFO 0.921 0.919 0.951 1.3 1.17 1.413 1.002 0.828 0.997 0.646 0.991 0.861 0.963 1.028 0.816 1.195 0.998
STL 1.014 0.799 1.272 0.757 1.685 1.069 1.165 0.435 1.158 0.999 0.397 1.048 0.721 1.174 0.932 1.375 1.005
WAS 1.086 1.27 2.184 0.72 0.906 0.819 1.196 0.536 0.875 1.043 1.098 0.906 0.741 0.887 0.699 1.031 0.998

Team | vs. bal bos chw cle det kan laa min nyy oak sea tam tex tor avg
BAL 1.071 1.154 0.883 1.489 1.312 0.707 0.75 0.638 1.013 0.752 1.163 1.224 0.561 1.283 0.995
BOS 0.959 1.033 1.065 1.162 0.944 0.978 0.876 1.04 1.055 0.885 0.723 0.98 0.969 1.33 0.997
CHW 1.285 1.027 1.059 0.945 1.003 1.059 1.279 0.888 0.666 1.634 0.698 0.567 1.374 0.515 0.995
CLE 0.685 0.846 1.067 0.952 0.776 0.693 1.704 0.676 1.015 0.786 1.337 1.172 1.428 0.863 1.004
DET 0.913 1.223 1.181 1.372 1.118 1.162 0.549 0.932 0.839 0.986 0.577 1.017 1.047 1.083 0.991
KAN 1.301 0.906 0.858 1.178 0.826 0.858 0.669 0.82 1.491 0.747 1.354 1.124 1.076 0.79 1.011
LAA 1.333 1.099 0.773 0.521 1.899 1.196 0.933 0.729 1.137 0.761 1.071 0.653 1.296 0.6 1.005
MIN 1.441 0.852 1.023 1.208 1.029 0.898 1.098 0.858 0.97 0.995 0.624 0.919 1.014 1.072 1.011
NYY 1.068 0.988 1.607 0.947 1.347 0.581 0.829 0.893 1.01 1.178 0.663 1.051 0.895 0.943 0.999
OAK 1.304 1.068 0.593 1.108 1.038 1.051 1.122 0.788 0.784 0.915 1.132 0.747 1.09 1.259 1.007
SEA 0.807 1.252 1.331 0.624 1.698 0.555 0.764 1.205 1.335 0.708 0.877 0.76 1.29 0.793 1.009
TAM 0.823 0.991 1.757 0.765 1.035 0.718 1.344 0.878 0.904 1.153 1.086 0.941 0.719 0.884 1.005
TEX 1.969 1.1 0.795 0.688 1.102 0.822 0.743 0.873 1.164 0.866 0.701 1.35 1.031 0.797 0.998
TOR 0.754 0.701 1.859 0.996 0.932 0.981 1.404 0.722 0.966 0.656 0.998 0.961 1.168 0.903 1.007

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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