examining home-field advantage
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Examining Home-Field Advantage. Phil Birnbaum www.philbirnbaum.com. Home Field Advantage (HFA). In baseball, home teams generally win 54% of games Why? Several possible explanations. Possible causes. Fan enthusiasm Familiarity with park Molding team to park Travel "Home Cooking" - PowerPoint PPT PresentationTRANSCRIPT
Examining Home-Field Advantage
Phil Birnbaumwww.philbirnbaum.com
Home Field Advantage (HFA) In baseball, home teams generally
win 54% of games Why? Several possible explanations
Possible causes Fan enthusiasm Familiarity with park Molding team to park Travel "Home Cooking" Umpires Batting Last Others
Can eliminate some Fan enthusiasm
Nope. Seems to be no correlation between HFA and attendance
Familiarity Only a little
Travel Nothing significant
Batting Last Not just in close games Pitching last also has its advantages
See "The Diamond Appraised" and "Scorecasting"
Recently: Umpiring "Scorecasting," by Tobias
Moskowitz and Jon Wertheim, released early 2011
Claims refereeing/umpiring is the true cause of HFA
Lays out some evidence for several sports
"Scorecasting" on umpiring Umpires call more strikes for home
team pitchers than for visiting team pitchers
The higher leverage (clutchier) the situation, the bigger the effect
Umpires actually favor the visiting team in less-important situations
"Scorecasting" on umpiring Authors claim umpiring/refereeing
accounts for almost all of HFA But … doesn't mesh with other
evidence of the incidence of HFA
HFA appears in all situations For instance:
When one team is ahead by 4+ runs early, that's low leverage. But HFA remains high
Home team outscores visitors regardless
Inning Overall When one team has 4+ run lead
1 +18% more runs
2 +10 +19
3 +11 +10
4 +8 +13
5 +10 +9
6 +8 +8
7 +7 +8
8 +6 +5
Umpires and leverage Mitchel Lichtman finds some effect
of clutchness on called strike HFA, but less than "Scorecasting" found
Me too
Other estimates are lower John Walsh, "The Hardball Times Annual
2011" Home team favored by 0.8 pitches per game Accounts for one-third of HFA
J-Doug, "Beyond the Box Score" Accounts for one-sixth of HFA
Dan Turkenkopf, "Beyond the Box Score" Accounts for one-eighth of HFA
Not just umpires? There might be other things going
on, not just umpires How can we find out? Look at things that don't involve
umpires
Like what? Maybe … fielding. Once a ball is in
play, umpires don't control whether it's a hit or an out
If defenses turn more balls into outs at home, would that show that HFA is more than just umpiring?
No, not really. Because …
Compensating for umpire bias … if umpires are more lenient
towards home batters, they get more balls and fewer strikes
More favorable counts Better hit balls Harder to field those balls So it could be umpiring after all!
Compensating for umpire bias Similarly in other sports
In hockey, the referee's main influence is in calling penalties
Home teams outscore visiting teams even at full strength
But, it could be because visiting teams have to play less aggressively out of fear of referee sensitivity
Same for soccer, basketball, etc.
How to tell? Need a measure of HFA that is not
influenced much by umpires How about wild pitches and passed
balls? Objective decision: ball eludes
catcher, runners advance
WP/PB home field advantage For 2000-2009 (God Bless
Retrosheet): Home teams:
539 WP+PB per 100,000 pitches Road teams:
557 WP+PB per 100,000 pitches 3.3 percent difference Statistically significant (barely)
WP/PB home field advantage On 0-0 counts only
Home: 511 WP+PB per 100,000 pitches
Road: 544 WP+PB per 100,000 pitches
Even larger effect
WP/PB home field advantage Overall difference: about 5 wins
over 10 years Works out to .0002 wins per game That's 1/200 of HFA Runs resulting from WP+PB are
1/50 of total runs Not perfect, but reasonable
Basketball Free throw shooting percentage is not
subject to referee bias HFA in foul shooting is about 0.2
percentage points in favor of the home team
Difference of 120 points a year 0.1 points per game Overall HFA is 3 points per game Again, seems reasonable
Speed skating There is a home-field advantage in
speed skating! Of course, that can't be because of
refereeing What could it be?
Another theory For some biological reason, humans just
perform better at home than on the road Testosterone levels: "players may have
tapped into a primal instinct to defend their own territory."
But, whatever: some intrinsic evolutionary reason is plausible, because HFA is pervasive and universal And none of the other hypotheses have
tested out
Competing guesses on HFA "Scorecasting"
Almost 100% umpires. Craig Wright, "The Diamond Appraised"
(1989) 5% crowd … 5% last AB … 10% familiarity
… 10% shaping team to park … 30% home cooking … 40% umpires.
Me (among others) 10% umpires … 80% intrinsic/testosterone
… 10% other.
Where to go from here? Need to come up with ingenious
ways to decouple umpiring from other factors
If you can think of any, let me know
For now, I think there's good evidence that umpiring is only a small part of what's going on
Acknowledgements Thanks to readers at my blog for
many comments, suggestions, and references on this topic
Mike Fast was especially helpful, pointing me to some of the studies mentioned here. Thanks, Mike.