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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jlefty

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On the one hand, if you remove Fenway from the equation (which certainly qualifies as "quirky", which is what we're looking for in stadiums built since Camden) the correlation jumps to 0.26, but on the other hand there are only 7 data points that qualify as "Not built since Camden" which might be too small to mean anything. For example, Having the word "Stadium" in the name of your stadium has 6 qualifying data points and a strong negative correlation of 0.42, but I'm pretty sure the fact is irrelevant.

Dec 03, 2010 07:11 AM