Increasing disparity in team strength in leagues

Posted on February 12th, 2019   

“The rich get richer and the poor get poorer”. This particular adage by Percy Shelley is most often used to describe the economic inequality caused by free market capitalism. However, it is strangely appropriate to describe what is happening to team performance in leagues in Europe. The strong are getting stronger as the weak are getting weaker.

In the 2000s, an apparent gap in team strength between the top 4 Premier League teams and the rest led people to start using the term the “the top 4” to refer to the teams that people considered consistently and clearly ahead of the rest in terms of performance. Just last summer, we saw Man City win the Premier League with a record breaking 100 points, indicating that there is likely a widening the gap in team quality in the Premier League. This is better illustrated in the animation below, which shows the distribution of points in the Premier League from 1995 onwards (when the format changed to a 20-team competition).


 

 

The existence of this phenomenon shouldn’t come as a complete surprise since good teams that perform well end up getting more money from commercial and sponsorship deals, matchday revenue, etc. as well as build up a history and reputation of success. These then allow them to recruit better players and staff and this positive feedback loop results in widening of the gap in team strength in the league. This isn’t something restricted to the Premier League either. In fact, we expect it to happen to a greater extent in some other leagues since some allow teams to negotiate their own televised matches deals independently (e.g. Spain) rather than having the televised matches deals negotiated centrally and the revenues distributed evenly across teams as occurs in the Premier League

We wanted to measure this effect in a more rigorous manner to quantify the change in team strength inequality, and to see how it compares across leagues. To do this, we can look at the distribution of points in the league table over time. More specifically, we are looking for inequality in the points distribution. Fortunately, there’s a well-established measure used in economics called the GINI coefficient that helps us to do this. It is commonly used to measure income inequality or wealth inequality, but we can use the underlying concepts behind the GINI coefficient to measure points inequality in leagues and track changes over time.

The way the GINI inequality measure works is… for any given season, starting with the weakest team (bottom of the league table), we measure the share of league points that the team accounts for and gradually include more teams until we consider all 20 teams in the league (at which point these will account for a 100% share of the points accumulated in the league). When these values are plotted, it creates a curve whose gradient characteristics encode the distribution of points in the league. In the case of a perfectly equal league where all teams get the same number of points, this graph will look like the line of equality (perfect triangle). Any deviations from this are a sign of inequality in the league, and the extent of the equality (or inequality) can be measured by the area under the curve relative to the hypothetical perfect equality case. The distribution of points in the Premier League and the corresponding GINI curve are shown below for reference.


The results below show how the league inequality has changed for the top 5 leagues in Europe since each of them changed format to their current league structure (18 teams for Bundesliga and 20 teams for the rest).






On average, across the past 10 years, Ligue 1 has been the most evenly matched league from the top 5 in Europe, followed by the Bundesliga. La Liga, Premier League and Serie A all have greater disparities in team strength in the league and are roughly similar to each other in that respect. A similar pattern is observed even if we just look at the inequality in league points last season. The Bundesliga had the most even distribution of league points, followed by Ligue 1, then La Liga, Premier League and Serie A.

Key results are summarised in the table below:

League 2017-18 season inequality (level of disparity in points between teams) Average inequality over last 10 seasons Inequality trend (change in inequality coefficient per year)
Premier League 0.14 0.13 +0.002
Serie A 0.16 0.13 +0.006
La Liga 0.13 0.13 +0.004
Bundesliga 0.10 0.11 +0.002
Ligue 1 0.13 0.10 +0.002

 

Crucially, all 5 leagues exhibit a trend of increasing points inequality over time, and it is statistically significant increase in all 5 cases (p<0.01). The inequality in team strength is increasing most rapidly in the Serie A, followed by La Liga, while the Premier League, Bundesliga and Ligue 1 appear to be the comparatively protected from the team strength positive feedback phenomenon.

This may be a slight problem for the future of football, since the sport may lose some appeal if the league positions become increasingly predictable over time. We wouldn’t be surprised if more rules were put in place to limit team spending in the near future to try reel this problem in, particularly in Italy.

We should enjoy this season’s competitive title race between Man City and Liverpool while it lasts. Leagues are likely to get increasingly less competitive over time.

 

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