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It has become a truism that the Western Conference is better than the Eastern Conference. Indeed, since 2000 there has only been one season that, collectively, the East was better than the West, 2007-2008. This year has seen a continuation of this trend, with the gap between the West and the East currently larger than it has been since the 2004 season.
The difference in quality exists on all levels. The West has won 9 of the last 13 NBA Championships, and John Hollinger’s playoffs simulation currently gives Western Conference teams a 76.2% chance of winning this year’s championship. It is also remarkably harder for Western Conference teams to even make it to the playoffs. The worst record to make the playoffs in the Western Conference in the past 13 years is 42-40, while it has been possible to make the playoffs in the Eastern Conference with a 36-46 record. In 6 of 13 years the 8th seed in the Eastern Conference playoffs have had a losing record, while in 2008 the Warriors failed to make the playoffs in the West with a 48-34 record! Finally, Eastern Conference teams have “won” 8 of the last 13 draft lottery’s, typically (but not always) signifying the worst team in the NBA.
The obvious place to look for an explanation is to the structure of the NBA, to see if there is anything that consistently gives Western Conference teams an advantage. On the whole, most conditions affect all teams equally. The bylaws of the NBA apply to all teams, meaning they all face the same salary cap restrictions and roster construction rules. All teams play 41 games at home and 41 games on the road, and all teams play (relatively) balanced out of division schedules. There are two potential structural determinants, travel and team location, but if anything these determinants benefit Eastern Conference teams.
Travel
While teams play slightly unbalanced intra-conference schedules, this has no bearing on differences in winning percentage between the two conferences. Teams do play a perfectly balanced inter-conference schedule: every Western Conference team plays every Eastern Conference team twice a season, once at home and once on the road. There is a difference, however, in how teams get to these games. The map above shows the distribution of NBA divisions. While the NBA has tried its best to create six divisions of geographically similar cities, the size of the Western Conference is about twice that of the Eastern Conference. The result of this is that Western Conference teams routinely travel more than teams in the East: in each of the last three seasons, seven of the top ten teams in miles traveled during the season were located in the West. Last year, 12 of the 13 teams to travel the least were Eastern Conference teams, creating a significant advantage by inducing less wear-and-tear on players’ bodies.
Team Location
Every year you hear about players that just don’t want to play in certain cities due to the perceived undesirability of living there. When Alonzo Mourning was traded to Toronto as part of the Vince Carter trade back in 2004, he flat out refused to report, and was eventually waived. On a recent Reddit AMA, Dallas owner Mark Cuban was asked why players don’t want to play in Toronto, and Cuban answered the question as if it is (and it probably is) a known fact that players don’t want to play in Toronto, meaning the Raptors have a structural disadvantage when attempting to sign or re-sign players.
But Toronto is the Eastern Conference exception to this rule. When you hear about teams or cities that players don’t want to go to, they’re usually in the Western Conference: guys don’t want to live in Minnesota, Salt Lake City or Sacramento. Of the teams that seem to have a strong appeal, only the Lakers and maybe the Mavericks in the Western Conference do. Most of the rest of the teams (Knicks, Celtics, Heat, Magic, Bulls) that players consistently want to play for are located in the Eastern Conference. Admittedly, this is only anecdotal evidence, but I would be hard pressed to believe an argument that stated that, on the whole, Eastern Conference team were less desirable free agent destinations than their Western Conference counterparts.
So if the structural explanations favor Eastern Conference dominance, how is it that the Western Conference is so much better?
Coaching
It is very difficult to measure the impact that coaching makes on a team, but could it be that Western Conference teams have better coaches? Most studies have found that coaching does not significantly impact team wins, with a few notable exceptions, but what if it did? In the Western Conference the average coach has been on the job for 3.55 years, while in the Eastern Conference this length is only 2.38 years (including both the firings of Mike Brown and Avery Johnson). If we make the assumption that general managers tend to keep good coaches around while firing bad coaches (not necessarily a safe assumption), the better coaches reside in the Western Conference. Given the evidence that coaching impact is difficult to measure, and the studies that suggest coaching impact is minimal, I’m inclined to discount this explanation.
Players
As you may have suspected, like most things in the NBA, at the end of the day it comes down to the quality of the players. Of the top 100 players in the NBA according to Win Shares 58 of them reside in the Western Conference. Furthermore, the average Win Share of a top 100 Western Conference player is 2.8, while the average Win Share of a top 100 Eastern Conference player is only 2.5. Not only does the Western Conference have a larger share of the top 100 player, it has a larger share of the better top 100 players.
As stated earlier, so far this year there is a bigger divide in talent between the East and West than in any year since 2004. This is especially interesting because not that much talent switched conferences during the off-season. While there was a lot of movement overall among talent, most of it (James Harden, Kevin Martin, Carl Landry etc.) was intra-conference, not inter-conference. In fact, among the top 100 players by Win Shares, only five switched conferences: Dwight Howard, Ryan Anderson and Omer Asik moved from the East to the West, and Jason Kidd and Aaron Afflalo moved from the West to the East. Furthermore there are three “new players” in the top 100: Damian Lillard and Andrei Kirilenko in the West, and Andre Drummond in the East. This may account for a small portion of the increase in Western Conference talent, but certainly not all of it.
The reason the West has increased its power is because of player improvement. For whatever reason (better coaching, playing against higher quality teammates, random chance), players that were already in the Western Conference have improved moreso relative to their Eastern Conference peers. Not a particularly sexy explanation, but the most likely.