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With the game on the line and fans on their feet, contentious calls tend to favor the home team, a bias that can explain a significant portion of the home field advantage in sports, according to research by professor Tobias Moskowitz.
"Home field advantage exists in every sport, at all times in history, and in all geographies," said Moskowitz, Fama Family Professor of Finance.
"And it's remarkably consistent," he added, citing statistics from the five most popular team sports—football, basketball, baseball, soccer, and hockey. In basketball, for example, both NBA and WNBA teams win about two-thirds of the games that they host. In baseball, the home team prevails roughly 54 percent of the time, whether it's an MLB game or played in Japan.
Moskowitz shared his research on home field advantage and findings on referee bias at a recent Myron Scholes Global Markets Forum. Based on work for his book Scorecasting: The Hidden Influences Behind How Sports Are Played and Games Are Won, coauthored with L. Jon Wertheim from Sports Illustrated, the presentation drew 200 people to Gleacher Center in downtown Chicago.
Uncovering referee bias
While officials may be tipping games toward the home team, the bias isn't intentional, said Moskowitz.
"We don't think this is conscious," said Moskowitz, who built on previous studies of soccer referee bias to uncover the connection to home field advantage. The cause, he says, is physchological, and in particular, related to social conformity.
"Basically, what's happening is referees start to see things the home crowd's way," Moskowitz explained.
In high-stakes game situations before making a split-second decision, referees seek both information from fans—and their approval. Referee bias becomes more evident, Moskowitz said, as the calls become more ambiguous—borderline strikes in baseball, for instance—and as crowds become more animated and opinionated.
Fear of blowing a call can cause referees to look for ways to "relieve some of that presure," Moskowitz said, "of having 50,000 screaming fans yell at you."
And the calls affect the scoreboard. In baseball, Moskowitz examined the strikezone and estimated that visiting teams receive 516 more strikeouts and are issued 195 fewer walks from home plate umpires over the course of a season.
"If you add up how much this is worth in terms of runs scored and everything else, that can explain a sizeable chunk of the home field advantage in baseball," said Moskowitz. "And, the same is true in other sports."
The behavior demonstrated in referee bias isn't restricted to sports, either.
"The idea of social conformity applies to a lot of settings," said Moskowitz. "It's one of the reasons, for instance, why mutual funds and analysts tend to herd and make some of the same recommendations."
Debunking the home field advantage myths
Before reaching their conclusions on referee bias, Moskowitz and Wertheim looked for evidence supporting the popular rationale on home field advantage.
They examined four possible explanations often espoused by broadcaster and fantasy league pundits and treated each one as a separate hypothesis. They mined data for isolated game events that could serve as a potential cause behind each effect in order to determine its bearing on home field advantage.
One way the authors disproved the influence of crowd support was studying basketball players' performance from the free-throw line. They found professionals sink 75.9 percent of their free throws whether lining up for the shot at home or on the road.
"We can't look at every situation, obviously, but if we find that crowd support doesn't have any effect on players in these isolated situations, it certainly questions how much of an effect they have in general on players," Moskowitz said.
Other conventional reasons—travel fatigue of visiting players or home team familiarity with the stadium—likewise were unsupported by game data.
"It doesn't mean that it's not there," said Moskowitz of the influence of drafting football players who thrive in cold-weather conditions or stacking a baseball lineup to suit a hitter-friendly ballpark. "It just may be a small effect and hard to detect in the data."
"You can't really disagree with data," said Evening MBA Program student Scott McIntosh after the presentation. Still, he was surprised by the evidence behind home field advantage.
Lindsay Brehm, '09, noted the application of business models to solve sports questions. "Even referees are subject to the regimens and influences we learn about in school," she said.
—Kate Fratar