If there’s one thing that NBA fans can never seem to agree on, it’s who’s the best. The debates about which team has the chance of winning a championship in a given season, which team has the strongest legacy, or who was the most dominant have raged on since the league came into existence. Through analyzing data about each team’s wins, losses, and point differential, we can hope to answer all of these questions.
Let’s take a look at what stats we’ll be using to wade through this data.
The statistic that is used to calculate the strength of a team over a given season is called “Elo.” It was originally created by Arpad Elo, a physics professor looking for a better way to evaluate the strength of chess players. Later, FiveThirtyEight applied this concept to NBA data. We will be visualizing that data to find the strength of NBA teams.
At its core, Elo is a very simple statistic. The only inputs are if a team won or lost a particular game, and how much they won or lost by. If a team scores an upset victory as the underdog, they get vastly more Elo than if they ran over a weak team (sorry, Knicks fans). Similarly, if a team wins by 40 points, they would gain more Elo than if they only won by 1 or 2 points. Finally, Elo was created for zero-sum games, so the losing team loses the exact amount of Elo that the winning team gains.
With that out of the way, let’s look at how each team’s Elo score has fared since the year 1977 up until 2015. We’ve averaged each team’s Elo by season, so the data isn’t as overwhelming like it would be if there was a point for each game. You can use the dropdown menu to select any one of the 30 teams in the NBA. Note that some teams haven’t been around too long, so their lines may start later on. Also, note that 1500 Elo is about average, but the number may fluctuate slightly by year.
In this chart, you can see the dynasties of great teams that NBA fans rave about. For example, the 1990s Bulls led by Michael Jordan peaked at nearly 1800 Elo in 1997, which is far above the 1500 average. You can also see Tim Duncan’s San Antonio Spurs of the 2000s and 2010s as a model of consistency. Their Elo remained above average from 1998 until 2015. It was a streak that allowed them to reach the playoffs for nearly 20 years straight while winning 5 NBA championships.
Since the number of points scored is a key element in the Elo equation, let’s take a closer look at how point differential relates to Elo over the history of the NBA. Green dots represent older seasons, and red dots represent more recent ones. Once again, you can select which franchise you’d like to look at with the dropdown menu.
Here, notice that a majority of the highest number of mean points scored over a season were during the 1980s. Among these high-scoring seasons, one team stands out-- the Denver Nuggets. The Nuggets hold the top 5 highest scoring seasons ever (all in the 80s), but they also allowed the most points against them by far.
On the complete other end of the spectrum, we have the early 2000s Detroit Pistons. Their airtight defense commanded by Ben Wallace stifled offenses and kept them from averaging over 90 points between the years of 2002 and 2005.
Finally, let’s take a look at how Elo correlates to what matters most, winning. Below is a stacked bar chart showing how many wins and losses each team racked up since 1977.
Looking back at our first visualization, we can see that teams with consistently high Elo, such as the Los Angeles Lakers, have a large amount of wins as well. Similarly, teams such as the Timberwolves who have spent a large amount of their existence below average Elo have over 400 more losses than wins. It seems like Elo is a pretty good predictor of which teams will finish with a winning or losing record.
So what do you do if your favorite home team has a consistently bad Elo? Don’t despair, as there’s one thing that Elo can never predict, and that’s upset potential. For example, remember that one of the few teams to beat Michael Jordan’s legendary 1996 Bulls were the meager Charlotte Hornets, who barely mustered a .500 win percentage that season. And don't forget about the 8th seed New York Knicks who made it all the way to the finals. Remember that basketball is unpredictable, and that’s what makes it worth watching.
While in other sports divisions are the main competitive entities within leagues, in the NBA, the eastern and western conferences are the main focus. Teams play more games against other teams in their own conference, and conferences also determine playoff seeding, with the winner of each conference playing each other in the NBA finals. It’s clear that conferences have a large impact on the competitive landscape of the league.
Due to this, there has been a dispute as to which conference has tougher competition. Many people argue that the Western Conference has been historically tougher, with teams like Kobe and Shaq’s Lakers leading the charge. Others say that the Celtics and Bulls of the East make it the more competitive conference. Let’s take a look at the data to see which side has more valid arguments.
In this stacked bar chart, we see the sum of the average Elos for each conference. You can use the slider at the bottom of the chart to select which year you’d like to look at. From this initial graph, it seems like the West is the stronger conference, as it has a consistently higher sum of average Elos over most eras! However, is that really the case?
Additionally, in the connected map, we depict all 30 NBA franchises at their respective locations, indicated by a circle. The size of the circle is dependent on the mean ELO value of that franchise within a specific year; the year can be adjusted using the slider at the bottom. As you adjust the year, you will come across times where the ELO value for a specific franchise is higher than it was in previous years, and also higher than that of other teams.
As you continue to move the slider, you will notice that from the majority of the time between 1980-present, the Eastern Conference maintained higher average ELO values than its Western Conference counterparts. We see this trend particularly in the 1990’s, mid 2000’s and 2010’s. Seeing the trends correlated with this data, it is clear that the Eastern Conference has maintained a stronger sense of supremacy over time.
In this chart, we depict the Average ‘ELO’ values for Eastern Conference and Western Conferencee NBA teams from the year 1976 up until the present. We chose the year 1976 because that was the first year that we started to see consistent data from the majority of teams represented by each conference.
To reiterate, ELO is a simple measure of strength based on game-by-game results, and the only inputs to calculate it are the final score of each game, and when and where it was played. Teams always gain Elo points for winning, but they get more credit for upset victories and for winning by larger margins.
As you can see, Eastern Conference teams held a higher average ELO for the majority of the time between 1976 and 2020. Seeing that Eastern Conference teams held a higher average ELO than Western Conference teams during that time, it is obvious that the Eastern Conference has been stronger than the Western Conference in terms of overall competitiveness.