Does MLS even need to worry about parity?

Update: Due to some analysis errors, the numbers on the original second chart were incorrect. Thank you to those who pointed this out! The updated second chart is shown below. While this doesn't change the conclusion that MLS is not the only league that displays a lot of parity, it does invalidate some of the discussion surrounding the second chart.

***

Let's talk parity in MLS. Not about whether it's "the only thing holding MLS back from success," or "what keeps fans interested in American soccer," let's talk about the extent to which it even exists.

For a long time, MLS has been seen of the pinnacle of parity. Whether people chalk this up to MLS's single-entity structure or just its use of a salary cap depends on who's doing the guess work, but regardless, the good MLS teams seem to lose more games than their equivalents in Europe, while the bad ones don't seem to stay bad for all that long. But what do the numbers say? Is MLS really all that it's cracked up to be parity wise, or are we seeing it through rose-colored glasses?

Well it depends on how you define parity. I think of parity as two things: firstly how much of a difference in quality there is between the good teams and the bad teams, and secondly how long teams retain their position in a league from year to year. If there isn't a big difference between the good teams and bad teams (like supposedly in MLS) then the league has parity. Similarly, if teams who do poorly one year in a league have a good chance of doing well the next year (also like supposedly in MLS) the league also has parity. Feel free to let me know about any other definitions of parity that you'd like to be looked at in the comments.

The chart below shows parity by the first definition: how many more points per game the best team in the league earned than the worst team, averaged over the past five years.

In some aspects, the chart shows what we'd expect, that MLS has a relatively small difference between its best and worst teams, while the top leagues in Europe (particularly La Liga in Spain) have large differences between their best and worst teams. But in other ways the chart shows us something new. While MLS may have a small difference between its best and worst teams, it isn't the only league of that sort, and in fact it doesn't even have the smallest difference. So while MLS may have lots of parity in this respect, perhaps we should stop treating it as a model league or the only one of its kind. In fact, we could even use this information to see what the consequences/benefits of parity are in other leagues to see what may lie ahead for MLS.

The next chart speaks to the second definition of parity: how likely teams are to change position in the league. The chart shows how much teams changed ranking each year in a certain league, averaged over the past five years (or technically the average of the standard deviation of each team's ranking over the past five years). For example, the average team in Brazil's Série A moved about 5.52 rankings from its mean ranking each year. So if the average team had a mean ranking of 10^th place in the last four years, their rankings over the past four years should have been something like 5^th, 15^th,15^th,5^th. Therefore a league with a high value here has a lot of change in the quality of teams over time, and therefore a lot of parity.

*Note that only teams who were in a league for two or more years were counted.

What jumps off the page here is how low MLS's value is -a mere 2.30- meaning that an MLS team is only expected to move 2.30 positions from its mean ranking each year. When we look at this in comparison to the other leagues shown, we see that in this respect MLS has by far the least amount of parity.

This seems contrary to everything we know about MLS. In DC United's turnaround from worst to third last year or in San Jose's steady decline to eighteenth place it seems like MLS teams move through the standings like nowhere else. This is especially true when we compare MLS to a league like La Liga, where Barcelona and Real Madrid hold the top spot (and only move by at most 1 ranking) each year. But what the data shows us is that when we look at the bulk of teams and not just the good stories that catch your eye, this trend does not hold true. Teams in MLS tend to stay bad or stay good longer than their counterparts in any of the other leagues studied.

So what does this mean for MLS? Well I think the most important thing here is to consider what is causing these differences in parity. If MLS has similar levels of parity (or perhaps even less parity) as leagues without its weird rules (salary cap, allocation money, etc.), perhaps its weird rules are not having their desired effect. On the other hand, MLS's rules may be what's keeping its parity so low, while at the same time other factor that don't affect MLS may be keeping parity so low in other leagues.

But no matter what you think about the causes, it would probably be good to spend a little less time worrying about parity in MLS. By one definition, MLS has the least amount of parity of ten major leagues, and by another MLS is just one league out of many. If other leagues with the same (or more) amounts of parity have survived, MLS probably will too.