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December 3, 2010

Ahead in the Count

Home Sweet Home Advantage

by Matt Swartz

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When I wrote my five-part series on home-field advantage in 2009, I noticed that it had been steady at about 54 percent for over half a century. It was 53.9 percent in the 1950s, 54.0 percent in the ‘60s, 53.8 percent in the ‘70s, 54.1 percent in the ’80s, 53.5 percent in the ‘90s, and 54.2 percent in the 2000s. However, in the last three years, we have seen home teams win 55.5 percent of the 7,288 games played, a very statistically significant difference. Does this suggest that a large change has actually taken place, or is it just a coincidence? If a change has taken place, what is causing it?

On one hand, there was only about a 1 percent chance that the league-wide home-field advantage of the last three years would be so far from the historical 53.9 percent of the last 60 years by sheer randomness. On the other hand, I clearly have cherry picked the last three years—I don’t plan on writing an article every year examining the previous three and declaring that it was 54 percent again—and perhaps the odds of getting any three-year period with such an extreme number may not be so small. However, if we expand the period to 2007-10, we still see a statistically significant difference in home-field advantage at the 2 percent level, and if we expand the period to 2006-10, we also see a statistically significant difference at the 2 percent level. Even the 54.68 percent home-field advantage from 2003-10 is statistically significantly different at the 5 percent level than the 53.97 percent home-field advantage of the last 60 years. The point is that I could have cherry picked a lot of starting and stopping points and still seen something so extreme.

The below table lists the league-wide home-field advantage since 1900:

Year

HFA

Year

HFA

Year

HFA

Year

HFA

1900

58.1%

1930

57.1%

1960

54.8%

1990

53.7%

1901

56.2%

1931

58.2%

1961

55.1%

1991

53.8%

1902

57.8%

1932

55.4%

1962

53.6%

1992

55.2%

1903

56.3%

1933

55.8%

1963

55.2%

1993

53.8%

1904

54.0%

1934

54.8%

1964

52.6%

1994

51.7%

1905

55.3%

1935

54.7%

1965

53.6%

1995

53.2%

1906

54.2%

1936

55.2%

1966

53.4%

1996

54.1%

1907

54.4%

1937

54.3%

1967

56.3%

1997

53.5%

1908

53.9%

1938

53.8%

1968

51.1%

1998

53.8%

1909

53.8%

1939

53.7%

1969

54.9%

1999

52.1%

1910

56.0%

1940

52.9%

1970

54.0%

2000

54.0%

1911

52.7%

1941

53.9%

1971

52.0%

2001

52.4%

1912

52.2%

1942

54.6%

1972

52.9%

2002

54.2%

1913

51.0%

1943

55.2%

1973

53.0%

2003

55.0%

1914

55.2%

1944

54.9%

1974

53.4%

2004

53.5%

1915

55.4%

1945

56.7%

1975

54.0%

2005

53.7%

1916

55.7%

1946

55.2%

1976

52.4%

2006

54.6%

1917

50.6%

1947

54.0%

1977

54.4%

2007

54.2%

1918

56.5%

1948

50.9%

1978

57.3%

2008

55.6%

1919

55.1%

1949

56.0%

1979

54.0%

2009

54.9%

1920

53.3%

1950

54.7%

1980

54.2%

2010

55.9%

1921

54.3%

1951

52.6%

1981

52.1%

 

 

1922

55.2%

1952

55.0%

1982

53.8%

 

 

1923

50.9%

1953

52.6%

1983

54.2%

 

 

1924

53.7%

1954

53.1%

1984

52.9%

 

 

1925

56.0%

1955

56.2%

1985

55.0%

 

 

1926

56.5%

1956

53.6%

1986

54.7%

 

 

1927

56.1%

1957

52.5%

1987

54.8%

 

 

1928

52.1%

1958

54.9%

1988

53.8%

 

 

1929

54.5%

1959

54.1%

1989

55.0%

 

 

You can start to notice how different 2008-10 look compared to other years from this table, but since the year-to-year fluctuations are very large even within one year, let’s look at the table again in three-year bursts. This will give a more clear sense of how abnormal the last three years are.

Year

HFA

Year

HFA

Year

HFA

Year

HFA

1900-02

57.2%

1930-32

56.9%

1960-62

54.5%

1990-92

54.2%

1901-03

56.8%

1931-33

56.5%

1961-63

54.6%

1991-93

54.2%

1902-04

56.0%

1932-34

55.3%

1962-64

53.8%

1992-94

53.7%

1903-05

55.2%

1933-35

55.1%

1963-65

53.8%

1993-95

53.0%

1904-06

54.5%

1934-36

54.9%

1964-66

53.2%

1994-96

53.1%

1905-07

54.7%

1935-37

54.7%

1965-67

54.4%

1995-97

53.6%

1906-08

54.2%

1936-38

54.4%

1966-68

53.6%

1996-98

53.8%

1907-09

54.0%

1937-39

53.9%

1967-69

54.1%

1997-99

53.1%

1908-10

54.6%

1938-40

53.5%

1968-70

53.5%

1998-2000

53.3%

1909-11

54.2%

1939-41

53.5%

1969-71

53.6%

1999-2001

52.8%

1910-12

53.6%

1940-42

53.8%

1970-72

53.0%

2000-02

53.6%

1911-13

52.0%

1941-43

54.6%

1971-73

52.6%

2001-03

53.9%

1912-14

52.8%

1942-44

54.9%

1972-74

53.1%

2002-04

54.2%

1913-15

53.9%

1943-45

55.6%

1973-75

53.5%

2003-05

54.1%

1914-16

55.5%

1944-46

55.6%

1974-76

53.3%

2004-06

54.0%

1915-17

53.9%

1945-47

55.3%

1975-77

53.6%

2005-07

54.2%

1916-18

54.1%

1946-48

53.4%

1976-78

54.8%

2006-08

54.8%

1917-19

53.9%

1947-49

53.6%

1977-79

55.2%

2007-09

54.9%

1918-20

54.8%

1948-50

53.9%

1978-80

55.2%

2008-10

55.5%

1919-21

54.2%

1949-51

54.4%

1979-81

53.6%

 

 

1920-22

54.2%

1950-52

54.1%

1980-82

53.5%

 

 

1921-23

53.5%

1951-53

53.4%

1981-83

53.5%

 

 

1922-24

53.3%

1952-54

53.6%

1982-84

53.6%

 

 

1923-25

53.6%

1953-55

54.0%

1983-85

54.0%

 

 

1924-26

55.4%

1954-56

54.3%

1984-86

54.2%

 

 

1925-27

56.2%

1955-57

54.1%

1985-87

54.9%

 

 

1926-28

54.9%

1956-58

53.7%

1986-88

54.4%

 

 

1927-29

54.2%

1957-59

53.8%

1987-89

54.5%

 

 

1928-30

54.6%

1958-60

54.6%

1988-90

54.2%

 

 

1929-31

56.6%

1959-61

54.7%

1989-91

54.1%

 

 

The important takeaway is that even though we see some pretty large fluctuations prior to World War II, there is a very steady home-field advantage in recent years that has barely moved until recently when it flirted with jumping in 2006 and then really took a big stride forward in 2008, and no three-year period since 1944-46 has had a home-field advantage this large, so the results seem to suggest something may be happening.

In last year’s articles, I also discovered that the magnitude of home-field advantage seemed to be very similar across teams, with year-to-year fluctuations in teams with big or small home-field advantages disappearing as quickly as they came (though the Rockies seemed to be one team that repeatedly had larger home-field advantages than other teams). However, if there has been a sudden league-wide change in home-field advantage, it may not have affected all teams equally, so I gathered the home-field advantage for all 30 teams over the 2008-10 period. But keep in mind that the margin of error for any one team is about +/- 9 percent, and that it is likely that one or two teams will be beyond that. In other words, one of these teams is more than 9 percent above or below their true home-field advantage capabilities.

Team

Stadium

Year Built

HFA 2008-10

Pirates

PNC Park

2001

21.3%

Tigers

Comerica Park

2000

18.7%

Rockies

Coors Field

1995

17.7%

Twins

Target Field

2010

16.8%

Rays

Tropicana Field

1998

16.0%

Red Sox

Fenway Park

1912

15.2%

Mets

Citi Field

2009

14.0%

Diamondbacks

Chase Field

1998

12.8%

Astros

Minute Maid Park

2000

12.6%

Nationals

Nationals Park

2008

12.1%

Blue Jays

Rogers Centre

1989

12.0%

Mariners

Safeco Field

1999

11.9%

Braves

Turner Field

1996

11.9%

Athletics

Oakland-Alameda County Coliseum

1966

11.8%

Orioles

Oriole Park at Camden Yards

1992

11.7%

White Sox

U.S. Cellular Field

1991

11.3%

Dodgers

Dodger Stadium

1962

11.1%

Yankees

Yankee Stadium

2009

11.1%

Cardinals

Busch Stadium

2006

10.3%

Giants

AT&T Park

2000

9.9%

Rangers

Rangers Ballpark in Arlington

1994

9.1%

Reds

Great American Ball Park

2003

8.6%

Indians

Progressive Field

1994

8.6%

Cubs

Wrigley Field

1914

7.0%

Padres

PETCO Park

2004

6.6%

Royals

Kauffman Stadium

1973

4.5%

Brewers

Miller Park

2001

4.5%

Phillies

Citizens Bank Park

2004

3.5%

Angels

Angel Stadium of Anaheim

1966

2.9%

Marlins

Sun Life Stadium

1993

2.7%

Home-field advantage for the average team has historically been about 8.0 percent (54%-46%), but 23 of 30 teams have larger home-field advantages than that in the last three years.

Although determining individual home-field advantages is a fool’s errand in most circumstances, there has been research showing that domed stadiums may show small home-field advantage trends than others. Additionally, I found that one particularly pronounced source of home-field advantage emerged in the number of extra-base hits that go for triples instead of doubles. I believe that this was because outfielders are better at playing the bounces in their own stadium, so road teams do not hit as many triples.

One of the major trends in ballparks came in 1992 when the Orioles built Camden Yards. This quirky stadium became a template for many other new “mallpark” stadiums built since then, each with their own idiosyncrasies. Since we know that quirks can cause extra home-field advantage, perhaps teams are beginning to exploit this more in recent years. While this may be a feeble theory, it is worth noting that the correlation between having a stadium built since Camden Yards was built has a .19 correlation with home-field advantage over the last three years. The older stadiums such as Wrigley Field, Angel Stadium, and Kauffman Stadium all are home to teams among the bottom six in home-field advantage, while the only  one in the top 10 is that decidedly quirky Fenway Park. It is difficult to say for sure that this is the cause, but if this is more than a fluke, my best guess is that teams are learning to take advantage of their quirky stadiums.

Even with this possible evidence, I am still skeptical that a change has taken place. While it is certainly possible that home-field advantage means more than it used to in baseball, I would still expect it to sit at about 54 percent in 2011, simply because there is such a historical precedent for flukes in league wide home-field advantage balancing out.

 What do you think? Is this a real change? If so, what else could be causing it? 

Matt Swartz is an author of Baseball Prospectus. 
Click here to see Matt's other articles. You can contact Matt by clicking here

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