Posted on May 15th, 2019
Assessing managers’ impact on a team’s performance isn’t as straight forward as with players. Unlike on-pitch actions that can be analysed in greater depth, details about the management of a team remain mainly behind closed dressing room doors and the only concrete in-game interventions we get to observe are largely limited to starting line-ups, formations and substitutions. Thus, in order to compare a manager’s influence on his squads’ performance, we need to consider higher level information; that is, budgets and expectations at the beginning of the season.
There are two principal ways of assessing manager performance, and we will provide an overview of these below in the context of benchmarking managers’ performance for the Premier League this season.
Team wage bill
A team is expected to perform better if it consists of better players. Good players are expected to be more expensive (though not necessarily linearly), so we can use the team wage bills as a proxy for team strength. Of course, a player’s wage is not only a function of his quality, but on average, that relationship should hold true. Two clubs spending the same on player wages, but one of them performing better is an indication that it is being managed better.
The differences in player wages among PL teams are very large. They range from £26MM for Cardiff to as high as £149MM for Man United (source https://www.spotrac.com/epl/payroll/). The graph below ranks the clubs by player wage bill.
Apart from Tottenham who manage to perform well despite a smaller wage bill, the difference of the big clubs from the rest is very evident. Within the block of high spenders, the Manchester teams seem to have formed their own sub-block of ultra-high spending. On the other end we have teams such as Cardiff, Huddersfield and Brighton whose player wages bills are less than a third of the top teams’ wage bills. Below is a graph showing the relationship between wages and points earned. Since we expect an element of diminishing returns with total team wage bill and league points (an infinite amount of money cannot bring an infinite number of league points), we fit a logarithmic curve to the data to quantify the trend.
Teams above the line are over-performing and teams below the line are under-performing with respect to their wage bills. The deviations from expectancy (residuals) can be more accurately summarised in the plot below (grey bars correspond to clubs that have changed their manager at least once during the season).
Jürgen Klopp is the clear winner here, with his team having obtained 24 points more than expected based on his player’s wages. He is followed by Wolves’ manager Nuno Espírito Santo and Manchester City’s Guardiola. Man United’s Mourinho/Solskjær fall towards the other end of the plot, having earned about 14 fewer points than expected based on squad wages.
Outperforming expectations from the start of the season
A team is expected to perform approximately as well as it has been performing in the recent past. If they have been consistently finishing near the top of the table in the most recent seasons, we expect them to match that performance in the current/next season. Any deviation from this self-set standard is an indication of a managerial under- or over-performance.
Based on results before the start of the season and using the well-known Dixon-Coles model for match predictions we can conduct simulations and get an estimate of the number of points teams are expected to earn against their 19 opponents in a season. Comparing these results with the final standings yields an alternate perspective on the teams that performed better or worse than expected. The chart below shows the percentage of excess points the teams managed to earn relative to the start of season expectations. Since there isn’t enough data to benchmark managers that have only been managing for part of the season, we are going to focus on clubs with a single manager throughout the season.
Once again, Klopp and Nuno Espírito Santo take up the spots at the top of the table, but this measure shows that Pellegrini has performed much better than expected. This is in contrast to his apparently poor performance using the player wages approach. So West Ham have indeed improved, but the improvement was not quite in line with their spending. The converse is true for Neil Warnock at Cardiff: Although they over-performed given their finances, they under-performed compared to past seasons, enough to get relegated.
From an analytics perspective, Jürgen Klopp is the manager of the year. He has had a fantastic season by any measure (including the 2 above), made more impressive by the fact that Liverpool’s wage bill is 20% smaller than Man City. To finish the season on 97 points, with just a single loss and 1 point behind Man City is a testament to his great year. He may have not won the Premier League, but he may yet win a Champions League medal to decorate and commemorate his performance this season.
Tags: Football, Premier League