Senior Fellow  Kevin A. Hassett

As the Boston Celtics celebrated their record 17th championship, the National Basketball Association suffered more accusations of biased officiating. During the Finals, former referee Tim Donaghy accused NBA officials of calling fouls to manipulate the results of playoff games.

Donaghy, embroiled in a gambling scandal, also pointed to Game 6 of the 2002 conference finals between the Los Angeles Lakers and Sacramento Kings. He asserted that the referees intentionally called more fouls on the Kings to try to deliver a win to the Lakers and extend the contest to seven games.

NBA Commissioner David Stern called the allegations "baseless" and accused Donaghy, a "convicted felon," of "turning on all his colleagues when Mr. Donaghy is the only one guilty of a crime."

Donaghy's last accusation is intriguing to an economist, because the league would certainly benefit from the described actions. NBA playoff series are best of seven, so they can run anywhere from four to seven games. If the series runs longer than four, then the league earns more gate revenue, and television broadcasters can sell more advertisements.

Of course, there's also a strong incentive for the league to be honest. If fans suspect foul play, they will presumably stop buying tickets.

How might a bias exist in practice? The easiest way might be for officials to favor the home team.

Serious P.R. Problem

There has been an increasing buzz among sportswriters that suggests the NBA has, at the very least, a serious public relations problem on its hands. These concerns were inflamed by the recent NBA Finals.

In Game 2 in Boston, the Celtics shot 28 more free throws than the Lakers. In Game 3 in Los Angeles, the Lakers shot 12 more free throws.

Is this just anecdotal, or can hard data and economic analysis be used to identify questionable patterns? To explore this issue, I gathered playoff and regular-season data on thousands of NBA games.

A first look at the numbers is troubling. Basketball is the one sport that should have the smallest home-field advantage. Every court is the same. Yet in the 2008 playoffs, the home team won 64 of 86 games--or 74 percent of the time. If we exclude the first round, where there are bound to be some blowouts, the home team won 34 out of 42, an 81 percent clip.

Skyrocketing Percentage

Travel might explain a modest home-court advantage. It could also be that adrenaline is stoked by the fans, and the pattern is completely innocent. There may be another answer.

Since the 2002 regular season, home teams won a little more than 60 percent of the time. In the playoffs, when a series might be extended by referees favoring the home team, the winning percentage skyrockets.

If the true odds of the home team winning were six in 10, as in the regular season, then the odds of observing 34 home victories in 42 games simply by chance are close to zero.

As may have been evident in the NBA Finals, home teams tend to get more calls. This would affect the outcome because foul calls lead to free throws; what's more, the home team can play more aggressive defense once it's aware that the officials are being kind to them.

Unfair officiating might also show up in shooting percentages.

Strange Occurrences

Once again, the statistics suggest something strange has been occurring in the playoffs. During the regular season since 2002-3, the home team generally gets called for 0.8 fewer fouls than the visiting team.

During the playoffs since 2003, though, the home-court advantage almost doubles, with the home team being called, on average, for 1.4 fewer fouls than the visiting team.

The same holds for field-goal percentage. In the regular season since 2002-3, the home team tends to shoot about 1.3 percentage points better from the field than the away team. In the playoffs since 2003, that difference jumps to 2.3 points.

This year, the difference has been 3.5 percentage points. This suggests the home team is allowed to play aggressively.

A skeptic might argue that the home-court advantage is magnified in the playoffs. Still, the data allow one to investigate.

How It's Done

Here's how. Later in the series, a home victory might be necessary for the games to be extended. In that case, the officiating bias might be greater. Sometimes a series might end before seven games if the home team wins. In those cases, the favoritism may be less. In the seventh game, the bias might disappear, as it no longer would serve any purpose. The series will end no matter what.

First let's look at Game 5. In the 2007 and 2008 playoffs, 25 series extended to at least five games. At times when the home team was leading three games to one, and another win meant the end of the series, the visiting team shot 1.1 percentage points better than the home team. When a home-team win doesn't end the series, the home team's field-goal percentage is 5.4 points higher on average than the away team's.

Let's turn to Game 6: In the 2007 and 2008 playoffs, in games where the home team was behind in the series, it was called for 4.1 fewer fouls on average than the away team.

The Seventh Game

In the seventh game the foul differential drops to just one during the past two years. That's little more than the regular season average.

All the data suggest there have been movements in the number of calls that are consistent with the suspicion that the NBA sought to extend series.

To be sure, such statistics prove nothing, since they are based on small samples. Yet the home bias in the playoffs, and the way in which it seems to change as a series progresses, is troubling, and worthy of further inquiry.

Kevin A. Hassett is a senior fellow and the director of economic policy studies at AEI.