By Andrew Puopolo

In recent years, the formats for the playoffs in both the NBA and NHL have come under increasing scrutiny. In the NBA, there have been numerous complaints about the imbalance of the two conferences. An Eastern Conference team without Lebron as its star player have only won 3 championships since 2000, and none since 2008. As a result, there have been calls to make the playoff bracket go from 1 to 16, disregarding conferences altogether.



The main argument behind this format change is to create fairness and ensure that the best two teams reach the NBA Finals. This was readily apparent in last year’s NBA playoffs. The two best teams in the league were clearly the Golden State Warriors and the Houston Rockets. However, under the current playoff format, these two teams meet in the Western Conference Finals. Meanwhile, a team from the weaker Eastern Conference (either the Cleveland Cavaliers or the Boston Celtics) had chance to make it to the NBA Finals. Although both Conference Finals series went to a full seven games, the Eastern Conference Champion Cavaliers were overmatched by the superior Warriors in the Finals, and were swept in four games, providing a bit of an anticlimax.



There is a similar phenomenon occurring in the NHL. In 2014, the NHL decided to partition their playoff format even more through the creation of divisions. As a result, teams could (mostly) only play teams within their seven or eight team division in the first two rounds of the playoffs. Thus, it is possible for the two best teams in the league to face off in only the second round of the playoffs. This year, the Tampa Bay Lightning and Boston Bruins have the two best records in the NHL, and although they both lost the first game of their best of seven Eastern Conference Quarterfinal Series, and since they both play in the Atlantic Division would meet in the second round of the playoffs.



This creates the same dilemma as to what the NBA is going through. While there are many arguments for why the current playoff formats are the way they are and should remain the same, I wanted to look into the fairness argument. If the NBA and NHL adopted “fairer” playoff formats, how would that affect individual team’s chances of winning the title or reaching the championship series?



Fortunately, using a similar methodology to the one used to predict the NHL playoffs that I published earlier this week, we are able to estimate these effects through simulation. For this analysis, we used the 2017/18 NBA playoffs (as this year the conferences are more equal) and the 2018/19 NHL playoffs. For each of these two seasons, we simulated the playoffs 250,000 times using two different seeding formats using our estimate for a team’s Glicko rating and rating deviation. For the NBA, we will simulate first using the current playoff format and then simulate using the proposed 1-16 format. For the NHL, we will simulate using the current playoff format and then simulate using the format used before 2014. The format before 2014 was the same as the format that the NBA currently employs, where the top 8 teams from each conference are seeded 1-8 regardless of their division. To make the simulations simpler, we will not reseed teams in the second round. As it turned out, this year’s NHL Western Conference shook out as a “true bracket” where 1 plays 8, 2 plays 7 etc., so for the purposes of this analysis we will focus on the Eastern Conference. It is important to note that the model used to predict future outcomes only relies on past game results and their timing (and nothing else). Thus, our model is very similar to the pure 538 Elo, and fails to take into account things like “Playoff Lebron,” which their Carmelo Model takes into account. For the technical details on the underlying model, please email andrewpuopolo@college.harvard.edu or reach out to me on Twitter @andrew_puopolo.



If we look at last year’s NBA playoffs, a true 1-16 bracket would have looked like this:

We now have what is desired, which is the Rockets and Warriors on opposite sides of the bracket.



Using the results of our two simulations, we wanted to compare every team’s chances of making it to the NBA finals as well as their chances of winning it.



In order to get a sense of our predictions, we will first look at the probabilities for each team reaching the NBA Finals under the current playoff format, given that they had at least a 1% chance of making it to the NBA Finals:



Obviously, since the model does not take into account factors other than game results, the Cavs and Warriors have a low probability of reaching the Finals, while the teams that dominated the regular season (Raptors and Rockets) have a higher chance. This plot is only intended to serve as a baseline so that the next plot can be put into context.



Next, we will take a look at the change in percent probability of each team reaching the NBA Finals under a 1-16 playoff format:

These results are exactly what we’d expect. Since the Warriors would not have needed to go through the Rockets to make the NBA Finals, their probability of reaching the Finals skyrockets. In addition, since the Celtics and 76ers have to now go through the Rockets and the Raptors have to go through the Warriors, their chances plummet. In fact, we see every single Eastern Conference team’s chances go down and every single team in the Western Conference has their chances go up.



This would seem to imply that a playoff change is needed. However, we will next take a look at the probability of a team winning the NBA Finals in order to see if the current playoff format is truly unfair.

While our plot looks incredibly similar to the previous plot, we see that the scale has changed drastically. In our previous plot, the Warriors chances of reaching the Finals increased from 21 to 40%, while their chances of winning the NBA Finals only increased from 13 to 15%. A similar story can be painted for the other teams. This is likely since the teams required to defeat en route to winning the NBA Finals does not change that drastically. The Warriors still likely would have needed to face the Rockets and Raptors in order to win the Championship, just in a slightly different order.



Next, we’ll take a look at this year’s NHL Eastern Conference. This year, three of the top four teams are in the same division. The Boston Bruins finished with the second record in the East, and in order to reach just the Eastern Conference Finals will likely have to defeat the 5th best team in the East (the Toronto Maple Leafs) and the runaway Presidents Cup winners (Tampa Bay Lightning). In a true 1-8 format, they would have faced the 7th place Carolina Hurricanes and 3rd place Washington Capitals.



If the Eastern Conference playoffs were seeded 1-8, this is what the bracket would look like:

We will go through a similar process to the NBA. However, we will examine one round earlier since the NHL partitions its playoffs into four groups instead of two. Thus, qualifying for the Eastern Conference Finals is most likely to change under the revised format.



First, we will take a look at each team’s chances of reaching the Eastern Conference Finals under the current format.

Here, we see that despite the fact that the Bruins finished 7 points ahead of the Penguins in the regular season, their chances of reaching the Eastern Conference Finals are 5% lower given that they likely must face the Tampa Bay Lightning in the second round. In addition, the Maple Leafs fall from 5th to 7th as a result of having to face both the Bruins and (likely) the Lightning.



Now, let’s take a look at the change in probabilities from the current format to the traditional 1-8 format that was used prior to 2014.

As expected, the Bruins see the biggest bump in probability due to facing weaker opponent in both rounds. Similarly to the NBA, we see that all four Atlantic Division teams see their probabilities increase, while all four Metropolitan Division teams see their probabilities decrease. The Bruins’ probability increases from 22 to 30 percent, which is about a 33% increase.



Next, we will take a look at the change in the probability of reaching the Stanley Cup Finals:



We see a very similar trend to the NBA. Although the Lightning’s chance increases the most (by 2% from 38 to 40), the difference is pretty small. It is interesting to note that the Bruins’ chance only goes up by about 1%, but this is likely due to the fact that their expected opponents to reach the Finals are roughly similar, just in a slightly different order.



Given these results, we can conclude that by switching the playoff format, the best teams are more likely to win the Championship and reach the later rounds of the playoffs. This difference is profound at the “critical round” of the playoffs (the round where the current paths have differed the most). In addition, we see that these differences are much more pronounced in the NBA than in the NHL, likely due to the increased parity present in the NHL.

However, these differences are rather small and have little change when predicting the overall champion. Given that the main argument behind changing the format is for fairness and crowning the best possible champion, we find that the effects are too small compared to the numerous arguments against changing the playoff format (travel, less exciting matchups etc.) in order to justify changing the playoff format. However, if the goal for a playoff system is to ensure that the two best teams compete for the championship in a winner take all series, then changing the playoff format might be worth exploring.



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