Elo Impact: Who are the EPL’s most effective managers?

Manager rivalry is one of the big themes of the season. Many of Europe’s most successful managers have converged on the EPL, sparking renewed and fierce competition between England’s biggest clubs as they battle on the pitch to achieve domestic superiority.  In the background there is another competition, one of a more individual nature. Guardiola, Mourinho, Conte and Klopp are seeking to establish themselves as the pre-eminent manager of their generation. As touchline galacticos, their rivalry mirrors that of Europe’s top players.

Success is often measured relative to expectation. Second place this season would probably be seen as a good finish for Liverpool, but not Man City. So Klopp and Guardiola will be judged against different standards. If Moyes guides Sunderland to a top ten finish he’ll win manager of the season.

For the same reason, it’s difficult to compare their track records. A manager may have won an armful of medals, but was it the result of years of sustained improvement or a few tweaks to an already excellent team? Can we compare the achievements of Wenger and Pulis, or Ferguson at Aberdeen and Ferguson at Man United?

To answer these questions we need an objective method for comparing the track records of managers over their careers. Not a count of the big cups in their cabinets, but a consistent and transferable measure of how much they actually improved their teams. In this post I’m going to lay out a simple method for measuring the impact managers have made at their clubs. I’ll then use it to compare the careers of some of the EPL’s current crop of talent.

Elo Scores


There is one measure of success that is applicable to all managers: to increase the number of games the team wins. The problem is that it is not easily comparable over time: a manager can move from a small club to a big club, or one league to another, and his win percentage will vary irrespective of the impact he had on each team.  However, there is a neat way of circumventing these issues, and that is to use the Elo score system.

Created by physicist Arpad Elo for ranking chess players, the Elo system has now been applied to a number of different sports, including the NFL and international football teams. The excellent site clubelo.com has adapted it for European club football. You can find all the details there, but here are the essentials: each team has an Elo score which varies over time as they win, draw or lose matches. The difference in scores between two teams is directly related to the probability of each team winning in a direct confrontation.

For example, Man United currently have an Elo score of 1778 and Barcelona 2013; the difference is 235 and under the Elo system this implies that Barcelona would have an 80% chance of winning the game (if played at a neutral venue). The full details of this calculation can be found here.

After two teams have played they will exchange points, with the exact amount being dependent on two things: the difference in their Elo scores before the game, and the outcome. For example, last weekend Man City drew 1-1 with Middlesbrough. As City were expected to win the game Middlesbrough gained 7.5 points and City lost the same number.

So how do we apply the Elo system to measure manager impact?

Manager Impact


We can assess the impact a manger has made by simply tracking the changes to the club’s Elo score since he took charge. I’ll refer to this as the manager’s Elo Impact. The neat part is that we can consistently monitor a manager’s record across multiple clubs by simply summing up all the changes to Elo scores over his career. Unlike win percentage, this works because the numbers of Elo points a team gains for a win is dependent on how superior they are relative to their opponent: in the Bundesliga, Bayern Munich receive far fewer points per win than Darmstadt 98.

Let’s look at a couple of examples. The two figures below show the Elo Impact of two managers across their careers: Alex Ferguson and Jose Mourinho (similar plots for Wenger, Guardiola, Klopp and Conte can be found here). For each manager, I’ve only included periods spent at UEFA clubs (omitting Wenger’s time in Japan, for example) and at clubs in the top two divisions of each country.

Figure 1 starts in 1978, when Alex Ferguson took over at Aberdeen, and ends with his retirement in 2013. The red line tracks the cumulative sum of the changes to his Elo score, bridging his move from Aberdeen to Manchester United in 1986.

Figure 1: the Elo Impact of Sir Alex Ferguson from 1978.

The first thing that strikes me is that his peak at Aberdeen – the 1983-84 season, when he won the Scottish league and European cup-winners cup – is almost level with his peak at Man United manager (his second Champions League and 10th EPL title in 2008). This implies that Ferguson’s impact at Aberdeen and United are comparable achievements. That’s not an unreasonable statement: Ferguson won 3 of Aberdeen’s total of four Scottish titles and is still the last manager to break the Old Firm hegemony. 
  
The striking thing about Mourinho’s Elo Impact (Figure 2) is that it is so much less volatile that Ferguson’s. Yes, the axis range is broader – Mourinho has had a lot of success in his career and his peak impact (at around 500) is substantially higher than Ferguson’s – but a quick estimate shows that Ferguson’s score fluctuates about 30% more. On closer inspection, this might be because Ferguson’s teams tended to win more of the big games but lose more frequently to weak teams than Mourinho’s (at least, until recently). However, this needs further investigation.

Figure 2: the Elo Impact of Jose Mourinho from 2004.

It’s worth emphasizing that the Elo score does not go up simply because trophies have been won, it does so if the team improves relatives to its peers. Jose Mourinho’s time at Inter is a good example of this. Despite winning the treble in his final season in 2010, Mourinho departed Inter having made little improved to their Elo score. This is because Inter were already the dominant force in Italy when he arrived, having won Serie A in each of the preceding three seasons. Put simply, it’s difficult to significantly improve the Elo score of a team that is already at the top. Guardiola’s time at Bayern Munich is another example.[2]

Who are the most effective managers in the EPL?


We can also use Elo Impact to rank managers. There is a question of how best to do this: by total impact (latest score), average impact over the career (score divided by total number of years in management), or by score this season. I’ve decided to provide all three, but have ranked managers by their total impact. The results are shown in the table below.

Total, average (per year) and 16/17 season Elo Impact scores for current EPL managers.

The top 6 are pretty much what you’d expect, with one very notable exception. Tony Pulis, who has never actually won a major trophy as a manager, leads the table. This is not crazy: Pulis has improved the standing of every major club that he managed (a plot of his career Elo Impact can be found here). In particular, over his two stints as Stoke City manager, he took them from a relegation threatened Championship team to an establish mid-table EPL team. 

I think that the example of Tony Pulis demonstrates one of the strengths of the Elo Impact metric – it is fairly agnostic as to where a team finishes in the league, so long as the team has improved. While we are naturally attracted to big shiny silver cups, some of the best work is being done at the smaller clubs. I fully acknowledge that repeatedly saving teams from relegation requires a very different managerial skillset to developing a new philosophy of football at one world’s most famous clubs; the point is that Elo Impact at least allows you to put two very different achievements on a similar footing. It’s a results-based metric and cares little for style.[1]

Guardiola is perhaps lower than some might expect, but then he only had a small impact on Bayern Munich’s Elo score during his tenure. A few successful seasons at City and he’ll probably be near the top of this table. Why is Wenger’s average impact so low? As this plot shows, he substantially improved Arsenal during the first half of his tenure, but has essentially flat-lined since the ‘invincibles’ season. Further down the table, Bilic's score has fallen substantially this season as West Ham have had a disappointing campaign so far. 

So what now?


I intend to develop Elo Impact scores for two purposes. First, I’ll track each manager’s scores over the EPL season to track who has had overseen the greatest improvement in their side. I’m happy to provide manager rankings for other leagues or individual clubs on request.  Second, as new managers arrive, I’ll look at their Elo track record to gain an insight on whether they’re likely to be a be success or not. 

It's going to be fascinating to see which manager comes out on top this season.

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Thanks to David Shaw for comments.


[1] Although you do gain/lose more points for big victories/losses.
[2] It is difficult to improve, or even just maintain, a team's Elo score once it rises above 2000. Few points are gained for winnings games and many are lost for losing them. Basically, the team is already at (or near) the pinacle of European football. For this reason I've made a slight correction to the Elo Impact measure: when a club's Elo score is greater than 2000 points, I've set the maximum decrease in a manager's Elo Impact to 10 points per game. Once the club's score drops below 2000, the normal rules apply.



Comments

  1. Another great post, Laurie!

    1) Can you control for risk? I.e., if 2/3rds of the time Tony Pulis will move you from 16th to 7th but 1/3rd of the time he'll get you relegated, whereas David Moyes will always bump you up from 16th to 14th, who is preferable? Maybe the reason City aren't going for Tony Pulis over Guardiola is that, even controlling for his phenomenal returns, he is too risky.

    2) I was struck, looking at Mourinho and Ferguson's comparison charts that Mourinho (final Chelsea stint excepting) appeared to move at his ELO peak, whereas Ferguson (at both Aberdeen and United) left when the wave had already crashed. For that reason, I'd be interested to see Wenger's ELO chart at Nancy, Monaco and Nagoya Grampus Eight - does it imply that he'll leave Arsenal on a high or a low?

    3) I reckon Big Sam would challenge Tony Pulis here. Would be interesting to see his ELO chart too.

    TW

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  2. There are a few problems I can see with this analysis, particularly the manager comparison at the bottom which, I think, explain why Pulis is so highly-ranked.

    1) The "ELO impact" does not, strictly-speaking, measure how good a manager you are. It measures how good you are relative to your immediate predecessor (and, further, with how they'd been performing immediately before they lost the job). Which would be fine, except that top clubs tend to have better managers. So, for example, Moyes is very low-rated because he took control of an already-declining Man Utd. team from one of the best managers in history and was unable to reverse the decline. Pulis, conversely, took over from relatively low-quality Championship managers and managers who had been fired for a series of poor results, giving him more chance to improve.

    2) It's biased towards managers who have managed lots of clubs. A manager will usually only take a few years at most to impose their philosophy on the club and get it performing to his potential (Fergusson is an exception to an extent because he focussed on youth a lot). So, someone like Wenger, who has managed only a handful of clubs, will naturally do worse than someone who has managed far more.

    3) It disadvantages managers of big teams. They aren't in a position to make the sort of big gains in ELO rating which Pulis made. So, whilst their success or failure is relevant, the exact size of the increase isn't really comparable.

    ReplyDelete
    Replies
    1. Thanks for your comments. I'll try to address each one in turn:

      1) I can see what you're saying here, but I don't entirely agree. It is true that the way to maximize your Elo Impact score is to take over clubs that are under-performing. However, there must be many, many more examples of managers that have taken over such a club and failed to make a significant impact than those that achieved what Pulis did at Stoke. Moyes is a bit of an isolated example in that he took over from the most successful manager ever. The drop in Moyes' score at United wan't actually that big though (you can find his plot here: eightyfivepoints.blogspot.co.uk/p/elo-impact-scores.html )

      2) Again, I think that this is only partly true. Managers that have worked at lots of clubs have rarely been successful at all of them and so their successes and failures tend to balance out (in terms of their Elo Impact score) in the long run. On the other hand, it's clear that those that remain at a single club for a long time tend to plateau after a while.

      3) This is certainly true for the very best teams: it's hard to make significant improvements in their Elo score and you don't get any credit for maintaining a team at a high level. I think it only affects a very select group of clubs though.

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    2. 1) I wasn't making a claim that the statistic is entirely uncorrelated with ability as a manager. I'm just saying that it's not a perfect correlation. In particular, managers who are well-regarded will tend to take high-value jobs and, thus, will probably get a lower Elo impact score relative to their actual ability. As such, I think this measure demonstrates the difference between actual and perceived ability as much as it does the actual ability itself.

      I don't think most of these rankings are unreasonable, but I also don't think you can convincingly use the results to compare Pulis to the other top managers, because his circumstances are simply too different for it to be a fair comparison.

      2) Yeah, I don't think managers always perform consistently with all clubs. Nevertheless, a top manager is likely to have more successes than failures (otherwise they're not a top manager), so a larger number of clubs will favour them.

      Perhaps I should revise my statement to say that the *variance* in Elo score increases with the number of clubs managed. For the managers at the top of the list, that is a benefit, but for those down the bottom it may not be. At the same time, a manager who consistently fails at Premier League level likely will not remain at that level, so it's not entirely zero-sum.

      3) It affects most of the top managers in the list to at least an extent. Pulis taking a team from the Championship to mid-table Premiership will (I think) give him considerably more points than Klopp taking Liverpool to the title would.

      The effect is also worsened because those managers are competing with each other for the limited points are on offer. Pulis, conversely, was competing with considerably lower-ranked managers.

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