Monday, May 2, 2011

NBA Playoffs, Game 7: How important is home-court? (Conf. Semis)

As the NBA playoffs are upon us, we will hear dozens of clichés thrown around by commentators.  The most irritating cliché is that the home team wins Game 7 of the series most of the time.  Since 1991, the home team is 36-10, a .783 win percentage.  This stat is always brought up without being put into proper context; as if to say having Game 7 at home causes a team to win.  However, I’ve never heard a commentator mention that the team with home-court advantage has a better record and usually is the better team anyway.  One would expect them to win a Game 7 at home, or on the road.  In this article and subsequent articles, I will try to find out how many Game 7s were won by the home team mainly because they were at home.

The table below tries to get the answer to the previous question. The basic premise of the table is that the more road wins there are in a series, the less home-court advantage matters. I separate Games 1-4 from Games 5-7 because the last three games of a series are probably more intense than the first four and home-court matters slightly, but still materially more in the last three games. Since 1991, in Games 1-4 the road team wins 32% of the time while in Games 5-7 the road wins 25% of the time. I rate, on a five point scale, the probability of the home team winning Game 7 mainly because they’re at home.  The five outcomes are: Yes, Probable, Possible, Doubtful, and No. This is scale far from perfect, but it appears sufficient to answer the question posed in this article.

Here are two examples of how the table works: The 1994 series between New York and Chicago produced no road wins, so it would be safe to say that the home team won Game 7 because of the home court advantage.  The 1994 Utah-Denver series produced two road wins, Utah winning that Game 7 was more likely due to them being a better team than due to home-court advantage.  The table below shows the 23 conference semifinals series that went to Game 7 in the last 20 post-seasons.

The home team won 17 of the 23 Game 7s, but how many of those 17 wins were mainly because of home-court advantage?  According to the table, only 11 of the 17 wins were at least probably due to home-court advantage alone.  That means that 6 of the 17 home-team wins probably had nothing to do with home-court advantage.  Home-court advantage in the Conference Semifinals' Game 7s appears to be overstated, as it did in the first round of the playoffs.

There's A Stat For That

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