How Bad is the NBA Conference Imbalance?

In the past few years the Western Conference teams have been hugely disadvantaged when it comes to making the NBA Finals. We’ll show here that, in fact, the amount of disadvantage of being the 1 seed in the West versus the 1 in the East is the same as a 3.5 point handicap (in 2015-2016). In this article, I show how to measure the degree of conference imbalance in the NBA

From the mid 2010’s until this year, the NBA talent has been heavily centered in the Western Conference. You could cite Lebron James’ eight straight Finals appearances in the Eastern Conference as evidence for how narrow the talent pool is in the East. Or, consider this: 12 of the last 15 First Team All-NBA selections have been Western Conference players. There is no doubt about it, the Western Conference is the seat of power in the NBA.

We want to explore two things in this article. First, just how imbalanced is it? I mean, how much more difficult is it to win a Championship out of the East than the West. Second, the common consensus is that the 2020 NBA Season is perhaps the most even the conferences have been in years.

The Method

Our technique is to look at how probabilities of winning the Championship change based on which conference you’re in. For instance, if we find that switching Milwaukee from the East to the West dramatically changes their chance of winning the Championship, then this is strong evidence for conference imbalance!

How can we compute the probability of a team winning the Championship? Well, using our NBA Ensemble (Recent) Ratings  we get the probability of teams winning in a particular matchup. Then, we can simulate the full bracket complete with the intricacies of a seven game series with alternating home court advantage. (Note: For the mathematically interested, computing the probability of each team winning against any other team is sufficient to run a Monte Carlo Simulation to estimate championship probabilities).

Now, since we want to compare conferences, we will compute the Championship probabilities in the traditional bracket. Then, we’ll switch the one seeds and see how their win probabilities change. This is our evidence for conference imbalance.

The Results

Let’s begin with a baseline. We simulated the 2020 Playoffs with seeding assigned based on current standings. The specifics we will look at is the probability of the one seeds advancing. For the actual bracket we saw the following probabilities of advancement:

The above graphic shows that in our simulations, Milwaukee advanced to the Conference Finals about 64% of the time and the NBA Finals about 40% of the time. As we might expect, because Milwaukee has been arguably the best team all year, the Lakers chances are a bit lower. For sake of completeness, when you simulate the entire bracket, Milwaukee wins the Larry O’Brien 21.9% of the time and the Lakers win 14.5% of the time.

Now, what happens when we switch the spots of the Lakers and the Bucks? By how much will the probabilities change? We did exactly this, pretending that the Bucks are the one seed in the West and the Lakers the one seed in the East. Here’s what we found:

This experiment screams one thing: The West is still harder to get through than the East. Perhaps more interesting, we can actually measure how much harder the West is than the East in points per game. What I mean is: how many points per game do we have to `spot’ the Lakers so that their probability of coming out of the West is 32.9% (the same as their unaltered probability of coming out of the East)?

The answer in 2020 is 1.5 points. How did we compute this? The Lakers’ chance of making the playoffs coming out of the East is 32.9%. If the Lakers would start every game in the Western Conference Playoffs up by 1.5, their chance of making it out of the West is also 32.9%. Therefore, we say the West is 1.5 points harder than the East in 2020.

How does this compare to past seasons?

Past NBA Conference Imbalance

We’re going to compare the conference imbalance in 2020 to the imbalance the 18-19 and the 15-16 seasons to see if the conferences really have balanced out. Remember, the last row in the following table is the amount of points per game we must give to the 1 seed in the West in order for them to have the same probability of making the Finals as if they came out of the East. This is our measure of difficulty of Western Conference versus Eastern Conference.

Season	2019-2020	2018-2019	2015-2016
Prob. East 1 Seed Makes Finals Out of East	39.9%	47.3%	30.0%
Prob. West 1 Seed Makes Finals Out of West	26.6%	31.2%	42.9%
Prob. East 1 Seed Makes Finals Out of West	32.9%	40.6%	18.7%
Prob. West 1 Seed Makes Finals Out of East	32.9%	37.0%	59.4%
Points Per Game Difficulty of West Versus East	1.5	1.5	3.5

We have some takeaways. First, the West is no easier this year than it was last year. This answers our second question at the beginning of this article. Second, even though these numbers don’t look like much, a 3.5 point handicap is huge. 3.5 points is more than the boost you get from playing at home every night. 3.5 points is the difference between the Lakers and the Thunder.

So, it still seems the conferences are (greatly) imbalanced. The Western Conference is significantly harder to win a Championship from than the East. Even with the ascension of Giannis, the continued success of the Raptors, and the dismantling of the 2020 Warriors, the West still remains king.

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