Editor’s Note: the following post is from Ed Feng, founder of The Power Rank, a sports analytics company that focuses on college football and basketball.
NBA teams spend all season fighting for home court advantage in the playoffs. They slog through a brutal 82 game schedule for that one extra home game in a playoff series.
Is it worth it? What is home court advantage in the NBA playoffs? I crunched some numbers to find out and put the results in this visual.
Declining home court advantage in the regular season
In the regular season, calculating home court advantage is easy because of the large numbers of games. With 1230 games each year, the regular season data in the above figure is simply the average margin of victory for the home team.
Home court advantage has dropped significantly since the mid 1980’s, probably because travel conditions have vastly improved. It’s much easier to relax on a chartered jet than in economy class, especially for tall people. However, the advantage has remained constant since the mid 1990’s.
How to Calculate Playoff Home Court Advantage
For the playoffs, home court advantage is more difficult to calculate because the stronger teams have more home games. To account for this, I propose considering a restricted number of games in each series. This home court calculation uses an even number of games in each series so that the higher and lower seed have the same number of home games.
Looking at this restricted set of games negates the effect of the stronger team. To see why, suppose Oklahoma City is 5 points better than Houston on a neutral court. With a hypothetical home court advantage of 4 points, Oklahoma City should win by 9 points over Houston at home. On the road, Oklahoma City will win by 1 point. The average home court advantage over these two games is 4. This is exactly what we assumed despite the differing strengths of the two teams.
Since the 2003 playoffs, when the NBA started having 7 games series in the first round, this method gives playoff home court advantage of 4.51 points. This is significantly more than the 3.17 points in the regular season over these same seasons. The uncertainties in the playoff and regular season estimates in the visual clearly show the statistical significance of this result.
If all playoff games are included, the home team wins by 5.05 points on average. With an uncertainty of 0.46 points, it is crucial to restrict the set of games to account for the differing strengths of teams.
Why home court is greater in the playoffs
In the book Scorecasting, Tobias Moskovitz and Jon Wertheim found that the crowd effect on referees is a large part of home court advantage. Twenty thousand screaming fans can make a persuasive argument to anyone. For NBA referees, this means that close judgement calls, like charges versus blocks, tend to favor the home team.
In addition, Moskovitz and Wertheim showed that referee bias increases with crowd size. This most likely explains the additional home court advantage in the NBA playoffs. The Lakers at home against the Spurs will draw more fans than a regular season contest with Washington at Charlotte.
What do you think? Have any research that other factors bump up home court in the playoffs? Leave a comment and let us know.
Thanks for reading.
Ed Feng is the founder of The Power Rank, a sports analytics company that focuses on college football and basketball. However, he is more excited about this year’s NBA playoffs than any season since Charles Barkley suited up for his hometown Philadelphia 76ers.