Assessing Parity in the ‘Big Four’ Sports

As a student at a Canadian university, I rarely get a break from hearing about the NHL and its wackiness. Seemingly every night there is at least one “unpredictable” upset, if not more. As if the Columbus Blue Jackets and Calgary Flames should be expected to lose every game – and the Pittsburgh Penguins should be expected to win every game. That’s simply not the reality of it, as the NHL is one of the most evenly matched pro sports leagues from top to bottom. Any given night a bottom-dweller can pull a “huge” upset on a supremely talented powerhouse.

The intense parity of the NHL, however, is not unusual, even for North America; it’s found in the other three of the “Big Four” professional sports associations – the MLB, NBA, and NFL. As a result, there’s a need for a parity ranking of the four leagues. Understanding the degree of parity in each of these four leagues will provide a more complete explanation of the wild upsets that make sports exciting to watch.

There are a multitude of ways to assess parity – or equality, fairness, etc. – in a league. One highly effective way would be to identify the upset factor of a league. The upset factor is defined as the expected winning percentage of a random underdog playing a random favorite. However, the statistical rigor required to produce the upset factor is too overwhelming for me as an arm-chair statistician. (If anyone has an effective algorithm for identifying the upset factor of a sports league, don’t hesitate to let me know and/or produce the results yourself.)

But in order to keep things simple and easily digestible, I’ve decided to compare the winning percentages of the best and worst teams in each league. This should give a general picture of the amount of parity between teams in a league. For example, if the best teams in a league are winning 90% or more of their contests, like in Spanish soccer’s La Liga, there is clearly a high degree of inequality. This method is obviously less accurate than the upset factor, but this isn’t brain surgery; I’m just trying to get a general indication for each league. Looking at the differences between the best and worst will be effective enough for the point of this article.

I’ve run through the numbers, and the results are as follows. The MLB and NHL are the most evenly matched leagues. The best teams in the NHL win roughly 63% of the time, while the worst win around 36% of their games. The best and worst of the MLB win around 60% and 38% of the time, respectively. The 2-to-3 percentage point difference between the two leagues’ top-bottom winning percentages is negligible when taking into consideration the additional 80 games that baseball teams play, which would naturally force their stats to regress to the mean.

The idea behind mean regression in sports is that, over the long run, a team’s performance will gradually hone in on their true playing ability. The more games played, the more a team regresses to their mean (average) playing ability. With only 82 games played per year in the National Hockey League, teams can overachieve to a higher degree than teams in Major League Baseball, where a whopping 162 games are played a year. With that in mind, the two leagues have essentially the same degree of parity.

The NFL ranks just below these two. Because NFL teams only play 16 games a year, I took the stats of the best teams over a five-year period, giving me 80 games to work with per team – which is similar to the 82 games played per year in the NHL and NBA. The result is that the best teams win around 70% of their games, while the worst win only 30%. Those percentages are somewhat surprising considering the cliche line “any given Sunday” that’s used to describe the high level of parity in the NFL.

The unexpectedly large margin between the best and worst teams may just be a product of the way in which I produced the NFL statistics – by looking at a five-year rather than a one-year window per team. I used four years worth of data for the other three leagues, while for the NFL I could only use the equivalent of one year (80 games being the rough equivalent of one NHL/NBA season). Consequently, the results are somewhat vague. Yet it’s apparent the NFL has less parity than the MLB and NHL, but probably not to the degree that the above winning percentages suggest.

Without question, the NBA is the most disparate league of the four. The best teams in the NBA consistently win around 74% of their games, while the worst teams win only 25% of the time. Intuitively, this makes sense. If you’re a basketball fan, you know that when the Miami Heat matchup with the Charlotte Bobcats, there’s a very small chance of a Bobcat upset – perhaps a 5 or 10 percent chance. That’s small, but it’s nothing compared to the European soccer leagues, where a team like Barcelona has nearly a 100% chance of beating a bottom-dweller. (If you don’t believe me, look at the betting lines for a Barcelona or Real Madrid game against a trash opponent.)

Aside from the unfortunate oddity of the NFL’s stats, there does appear to be a clear-cut hierarchy of parity in the “Big Four” leagues. The MLB and NHL have the most evenly matched teams, with the NFL being somewhat less balanced. Undoubtedly, the NBA has the least parity of the four.

So for the NBA, there is a justifiable reason to be pumped/depressed (depending on your side) when a lottery-bound team of no-names escapes with a win over a league-leading powerhouse. But there’s hardly a reason to worry when your beloved Chicago Blackhawks lose in regulation to the Calgary Flames. They’re still good (if not the best), and they’ll probably end up making a deep playoff run. It’s the same for the MLB – and to a lesser degree the NFL. Upsets aren’t that unusual, so don’t fret over them.

Upsets are what make sports exciting. It’s just that not all upsets are created equally.


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