Nylon Calculus: How conference imbalance affects playoff results in the NBA

It’s no secret that the Western Conference in the NBA has been appreciably better than the Eastern Conference for some time. While many commentators expect the disparity to even out or flip at some point, the imbalance has been going on long enough that NBA commissioner Adam Silver is looking at re-seeding the playoffs one through sixteen based solely on record without regard to conference.

I have been looking into some translations of regular season performance to the the playoffs. I am particularly interested in the last fifteen years, which coincides with the “no hand check enforcement era” and the” post-D’Antoni Phoenix Suns 7 Seconds or Less era.” It’s also an era of Western dominance.

That dominance is pretty nicely shown in this distribution graph of the win percentage in the regular season by Western and Eastern conference playoff teams over that time.

In that time, the average regular season wins for a Western Conference playoff team has been 52.6 (with the 2011-12 lockout season adjusted to an 82 game pace). In the East, the average playoff team has won 47.8 regular season games, almost five fewer than the West. The lockout shortened 2011-12 is the only season with conference parity for playoff team wins in the last fifteen years, as shown below.

The disparity has been more than which teams qualify for the playoffs, it’s also had a significant impact on how far teams go in the playoffs. The number of wins a team gets has been a better indicator for how far a team will go in the playoffs than net rating over this time, likely because while the two are closely related by the end of the season, only wins affect playoff seeding and home court advantage. Due to the consistent conference disparity over the last fifteen years, an Eastern Conference team has won an average 2.3 more games in the playoffs than a Western Conference team with the same record.

For example, the analysis indicates that a 48-win team in the East could expect 5.3 wins, getting them into the second round, while, on average, that 48-win team in the West goes home after a fun little series ending in a first-round loss. (The regression formula was: Playoff Wins = -17.3 + .39 * Win Percentage -2.33 If Western Conference)

The key to this Western dominance in this era, by the way, has come consistently on the offensive side of the ball. Comparing the average offensive rating (ORTG) of playoff teams, the Western teams are consistently better, while the defensive rating (DRTG) is much more even.

First offensive efficiency:

Then defensive efficiency:

The NBA commentariat from the ex-players on TNT, to the grizzled print columnists, and the fan blogs are almost pathologically focused on playoff success and ringzz. To me, the playoff over everything focus has gone a bit far. Still there’s no denying that a good regular season followed by a quick exit leaves a bad taste, though we should remember the conference context comparing those playoff runs.

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All that said, the top eight teams in both conferences as of Monday were on track to average 51 wins.