How Easy is the East? (07/08/16)

By Sean Pyritz @srpyritz
Kevin Durant has made a career of dazzling spectators with his silky stroke, but it is a different kind of stroke – with pen in hand – that has many believing the ink on next season has already dried. Joining forces with the Splash Brothers – maybe we should call them the Three Bombardiers, or not – has sparked a media firework show of outrage well past Independence Day. The grievances stretch from accusations of weakness to “cheating” to win, but what is being overlooked is how this momentous decision puts a death knell to my story last week. For this reason, Kevin Durant, without naming names, is hereby blacklisted from my articles. Instead, this week we are going to explore the difference between the Eastern and Western Conferences.

In hopes of drawing inspiration for this week's article, I was flipping through my copy of the 2002 Pro Basketball Prospectus by John Hollinger when I came across an interesting question – how much easier is the East? I will borrow and expand upon his methodology in order to explore this question over the last twelve seasons – since the league expanded to 30 teams. But first, let's take a look at just how dominant the West has been.

Since the 2004-2005 season, Western Conference teams have won 52.3% of their games, while their Eastern counterparts have won just 47.7%. Every game within conference adds a win and a loss to the overall conference record, so the difference in winning percentage comes from the cross-conference matchups. In the 5,220 games between the East and the West over the past twelve seasons, the West has won a whopping 56.5% of these contests – a win percentage equivalent to a 46-36 record.

The dominance is even more pronounced if we take a look at playoff teams in each conference. If we combine the win-loss records of each franchise across the past twelve seasons we can demarcate the average cutoff win percentage for a playoff team in the Eastern and Western conference - .490 and .525, respectively. Using these thresholds and the combined records, only four East teams would have qualified as playoff teams in the West on average. On the other hand, 12 of the 15 West squads would made the playoffs in the East – quite the dramatic difference. Finally, if we structured the playoffs so the top 16 teams overall made the playoffs, as some have advocated for, 11 of the 16 spots would be taken by West teams, including six of the top eight, as seen in the table below.

Now that we've established the strength of the Western Conference, let's take a look at how much easier the Eastern Conference truly is, starting with Hollinger's method. In his book, he compares how an average team would perform as a member of each conference. In order to do this, we need to find the winning percentage of the “average” East and West team on a balanced schedule of 41 games versus each conference. The win percentage for an average East team is .468 and for an average West team is .532. Using these averages, we can place a completely average team in each conference and compare the predicted records. For example, the average team on a Western Conference schedule would lose 28 games (.532*52 games) versus the West for a record of 24-28, and lose 14 games (.468*30) versus the East for a record of 16-14 – an overall record of 40-42. If placed in the Eastern Conference, an average team would have an expected record of 41-41, only a one win difference – or more precisely 1.5 wins if we do not round. This result is consistent with the assertion Hollinger made in his book many years ago.

Zooming in on each individual season, the difference is to the benefit of being in the Eastern Conference in each of the last 12 seasons, with the exception of 2008-2009, when there was a 0.3 win benefit of being in the West. In 2013-14, the difference between being in the East and West for an average team was 2.9 wins, the largest in this time period. Over the two seasons since then, the difference has steadily dropped down to just a 0.3 benefit this past season. Last season also marked the only time in this era that the East would place more teams in the West playoffs than vice versa.

The average team methodology from Hollinger may seem a bit too abstract or hypothetical so I wanted to present it in a different way that perhaps is more intuitive and yields the same results. Instead of introducing a mythical “average” team into each conference, we can simply compare the change in wins between East and West when the schedule is balanced. Over the past twelve years, the actual difference in wins between each conference is 3.8 – 42.9 for the West versus 39.1 for the East. If we use the balanced schedule adjusted win percentages found earlier, the difference in wins between the two grows to 5.3. This is accounted for by an increase of wins in the West to 43.6 and a decrease in the East to 38.4 wins. Therefore, the benefit of being in the Eastern Conference and playing 50 games against the East is 1.5 games, as we saw above. If the East was so much easier than the West, we would expect a larger benefit to being in the Eastern Conference in terms of wins. While there is a justifiable perception that the West is stronger than the East, history shows this strength is overstated. The benefits of being an Eastern Conference team are not as pronounced as you may have been told.

Look out for future investigation into the disparity at the top of the league, with the majority of the elite teams historically concentrated in the West.