Historical Trends in Home-Field Advantage
by Cyril Morong
Click here to see my sabermetric blog called Cybermetrics
This paper was published in the Baseball Research Journal, from the Socitey for American Baseball Research. Special thanks to David Smith for providing me all the necessary data from the Retrosheet files
From 1901-2002, the average seasonal difference between a team’s home winning percentage and its road winning percentage was .082.1 But has it changed much over the last 100 years and has the change been significant? What teams have enjoyed an especially good home field advantage?
Figure 1 shows how the average home field advantage changed from 1901-2002.
Now, there is a slight downward trend over the century, but quite a bit of year-to-year variance. The average home advantage in 1931 was .164, and then fell rapidly and dramatically afterwards. Then there is the huge spike to .146 in 1978, the biggest advantage since 1931. A decade-by-decade summary might be a little more interesting. This is given in Table 12 which clearly shows that the home field advantage has declined over time. Yet the second decade has the second lowest average. So there is a trend, but anomalies as well. Has the change been statistically significant? Yes.3 But is it significant in a baseball sense? When the average advantage is .103, it means a home winning percentage of about .552. When the advantage is .07, it means a home winning percentage of .535. This difference over 81 games is 1.36 wins. I leave it to each reader to decide if that is significant in a baseball sense. The third column projects how many more games a team would win at home above an even split. For example, in the first decade an even split would give a home team 38.5 wins. But with a .1042 difference between their home and road percentages (a .552 home winning percentage), they would win 42.51 games at home. Decades from the 1960’s on use 81 games.
Table 1
|
Decade |
|||
|
Average Advantage |
Extra Home Wins for Full Season |
||
|
1901-10 |
0.1042 |
4.01 |
|
|
1911-20 |
0.0740 |
2.85 |
|
|
1921-30 |
0.0928 |
3.57 |
|
|
1931-40 |
0.0976 |
3.76 |
|
|
1941-50 |
0.0922 |
3.55 |
|
|
1951-60 |
0.0784 |
3.02 |
|
|
1961-70 |
0.0796 |
3.22 |
|
|
1971-80 |
0.0752 |
3.05 |
|
|
1981-90 |
0.0800 |
3.24 |
|
|
1991-2002 |
0.0700 |
2.84 |
Home stands are not as long as they used to be and teams now travel by plane. This might account for the historical trend. But notice that the difference between the 1940’s and 1950’s is not too great and that the 1980’s was higher than the 1970’s. The average from 1901-1950 was .091 and since it has been .076. This seems like a small difference.
Table 2 shows the top teams in each decade. A team had to play at least five years in the decade to qualify.4
Table 2
|
Decade |
Leader |
Advantage |
Extra Home Wins for Full Season |
|
1901-10 |
Philadelphia (AL) |
0.2289 |
8.81 |
|
1911-20 |
Brooklyn |
0.0936 |
3.60 |
|
1921-30 |
Cincinnati |
0.1277 |
4.92 |
|
1931-40 |
Cleveland |
0.1183 |
4.55 |
|
1941-50 |
Boston (AL) |
0.1947 |
7.50 |
|
1951-60 |
Cincinnati |
0.1113 |
4.29 |
|
1961-70 |
Houston |
0.1895 |
7.67 |
|
1971-80 |
Houston |
0.1202 |
4.87 |
|
1981-90 |
Minnesota |
0.1731 |
7.01 |
|
1991-2002 |
Colorado |
0.1658 |
6.71 |
Table 3 shows the top ten teams since 1901 that existed in one city for at least ten years. Changes in ballparks for these teams was not taken into account. (Table 3 assumes an 81 game home schedule for all teams).
Table 3
|
Team |
Advantage |
Extra Home Wins for Full Season |
|
Rockies |
0.1433 |
5.80 |
|
Marlins |
0.1216 |
4.92 |
|
Astros |
0.1190 |
4.82 |
|
Athletics-Phi. |
0.1077 |
4.36 |
|
Red Sox |
0.1045 |
4.23 |
|
Browns |
0.0942 |
3.81 |
|
1st Senators |
0.0911 |
3.69 |
|
Braves-Bos. |
0.0910 |
3.69 |
|
Giants-SF |
0.0900 |
3.65 |
|
Yankees |
0.0881 |
3.57 |
The lowest home advantage belongs to the Orioles, at .051.
Has a big home field advantage been an aid? Not really. The overall winning percentage of the teams with the twenty-five highest single-season home advantages is .492. For the twenty-five worst teams it is .498. The only one of the best twenty-five to win a pennant was the 1987 Twins. Table 4 shows the best ten home field advantages since 1901. It uses the 77 home game and 81 home game schedules where appropriate.
Table 4
|
Team |
Year |
Advantage |
Extra Home Wins for Full Season |
|
Philadelphia (AL) |
1945 |
0.356 |
13.71 |
|
Philadelphia (AL) |
1902 |
0.338 |
13.01 |
|
Boston (AL) |
1949 |
0.337 |
12.97 |
|
Colorado |
1996 |
0.333 |
13.49 |
|
Minnesota |
1987 |
0.333 |
13.49 |
|
Houston |
1978 |
0.321 |
13.00 |
|
Philadelphia (AL) |
1908 |
0.319 |
12.28 |
|
Chicago (AL) |
1903 |
0.315 |
12.13 |
|
Chicago (AL) |
1902 |
0.312 |
12.01 |
|
Boston (AL) |
1952 |
0.311 |
11.97 |
Despite the trend towards a lower home field advantage, 2003 saw a fairly big one. The average home field advantage was .099. There were also seven teams that had at least a .160 advantage, which is just about twice the historical average. With 23.33% of the teams being above the .160 mark, this is the highest percentage since 1986 when seven of the twenty-six teams were above .160. This past season was the 29th highest percentage of teams going above .160. Table 5 shows the home advantage for all teams in 2003.
Table 5
|
Team |
Advantage |
Home W |
Home L |
Road W |
Road L |
|
Colorado |
0.296 |
49 |
32 |
25 |
56 |
|
Montreal |
0.259 |
52 |
29 |
31 |
50 |
|
Oakland |
0.222 |
57 |
24 |
39 |
42 |
|
Chi White Sox |
0.198 |
51 |
30 |
35 |
46 |
|
Texas |
0.185 |
43 |
38 |
28 |
53 |
|
Florida |
0.185 |
53 |
28 |
38 |
43 |
|
San Francisco |
0.166 |
57 |
24 |
43 |
37 |
|
Anaheim |
0.149 |
45 |
37 |
32 |
48 |
|
Philadelphia |
0.148 |
49 |
32 |
37 |
44 |
|
Boston |
0.136 |
53 |
28 |
42 |
39 |
|
St. Louis |
0.136 |
48 |
33 |
37 |
44 |
|
Baltimore |
0.122 |
40 |
40 |
31 |
51 |
|
Atlanta |
0.111 |
55 |
26 |
46 |
35 |
|
Tampa Bay |
0.111 |
36 |
45 |
27 |
54 |
|
Houston |
0.111 |
48 |
33 |
39 |
42 |
|
Cleveland |
0.099 |
38 |
43 |
30 |
51 |
|
Los Angeles |
0.086 |
46 |
35 |
39 |
42 |
|
Seattle |
0.086 |
50 |
31 |
43 |
38 |
|
Arizona |
0.074 |
45 |
36 |
39 |
42 |
|
Minnesota |
0.074 |
48 |
33 |
42 |
39 |
|
San Diego |
0.074 |
35 |
46 |
29 |
52 |
|
Detroit |
0.037 |
23 |
58 |
20 |
61 |
|
Pittsburgh |
0.037 |
39 |
42 |
36 |
45 |
|
NY Mets |
0.030 |
34 |
46 |
32 |
49 |
|
Cincinnati |
0.012 |
35 |
46 |
34 |
47 |
|
Chi Cubs |
0.000 |
44 |
37 |
44 |
37 |
|
Kansas City |
-0.024 |
40 |
40 |
43 |
39 |
|
NY Yankees |
-0.028 |
50 |
32 |
51 |
29 |
|
Toronto |
-0.049 |
41 |
40 |
45 |
36 |
|
Milwaukee |
-0.074 |
31 |
50 |
37 |
44 |
Notes
1. This is just a simple average, adding up every team’s single season advantage and dividing by the number team-seasons. Season with longer schedules are not given extra weight.
2. Again, this is just a simple average. The overall home field advantage is added up for each of the ten seasons and then is divided by ten. Seasons with more teams or games don’t get extra weight. The low figure for the 1911-20 period is not affected much by the Federal League, which had a about a .084 advantage during its two seasons.
3. Using the means test, the difference between the first decade and the last is significant, with a Z-score of 3.97. Also, here is the standard deviation for all teams for each decade: 0.0914, 0.0848, 0.0769, 0.0787, 0.0857, 0.0855, 0.0831, 0.0837, 0.0773, 0.0810. This shows that the dispersion in home field advantage across teams has not changed much since 1901. The correlation between year and the average yearly home advantage is -.247. It has a t-value of –2.55, which iss statistically significant.
4. The advantage listed for teams that changed parks in their respective decade only includes data from the park they played the most seasons in. Only one of those teams, the Indians of the 1930’s, actually did not have the biggest advantage when only their most commonly used stadium was considered. The Reds would then actually be a little higher, at .1188. The following are the teams that changed parks and their home advantage for the entire decade: Philadelphia (01-10), .2021; Cleveland (31-40), .1234; Houston (61-70), .1783; Minnesota (81-90), .1438; Colorado (91-2002), .1433. For all of them, except Cleveland, they would still have the highest yearly average even if all years of the decade are used.
Sources
Retrosheet generated data from David Smith, head of Retrosheet.
Yahoo! Major League Baseball Web Site