Friday, 11 May 2012

Chelsea's League Form Under Villas Boas and Di Matteo.

This season's highest profile managerial departure rather predictably came at Chelsea following their 1-0 defeat away to WBA on the 3rd of March.The defeat left Chelsea three points adrift of fourth placed Arsenal,seven shy of Tottenham and confirmed their irrelevance in the Championship race where Manchester City were already swinging away in a 20 point lead over The Blues.

After an opening day draw at Stoke,an early season run of four wins in all competitions hadn't been bettered and fatally for Villas Boas two mid season four game sequences of winless games had recently stretched to one of five games.In the currency most usually used to describe a team's well being,his Chelsea team had averaged just 1.7 points per game.Fantastic if you were managing a mid table team on a budget,but a totally unacceptable level of form for a team used to challenging for top spot.

Abramovich must enter every season with a mind to a replacement candidate for his top job should the need arise and Roberto Di Matteo was swiftly promoted from within.He has now taken charge of Chelsea for ten Premiership matches and has interspersed this mundane fayre with a Wembley rout of their near rivals,Spurs and Cup Final victory over Liverpool and has plotted a course past Barcelona to reach the Champions league final against Bayern Munich.

However,critics of Di Matteo are quick to point out that his points per game haul is inferior to that of Villas Boas.In the Premiership Chelsea have average 1.5 points per game since the mid season sacking and although they have around a 36% chance of qualifying for next year's Champions League as holders,they cannot do so by their EPL position where they can finish no higher than 6th.Had they kept accumulating points at the pre sacking rate of 1.7 per game,they would current have around 65 points,making their chances of qualification through the EPL route somewhat on par with the chance currently enjoyed by Newcastle.

Points per game averages can be skewed by the arbitrary awarding of three points for a win.Few would argue that a win is three times better than a draw,so a more objective approach is to look at a team's success rate,where a draw is treated as half a win.If we do this for each portion of Chelsea's season we again see AVB coming out on top of RDM in performance in the Premiership with success rate mirroring the difference in points per game for each manager.

So by both standards,AVB appears to have got more out of Chelsea on a league day than did RDM in subsequent midweeks and weekends.

Chelsea's EPL Raw Points Per Game and Success Rate Record,2011/12.

Chelsea Team Performance. Villas Boas. Di Matteo.
Points per Game in Premiership. 1.70 1.50
Success Rate in Premiership. 0.61 0.55
Success Rate.All Games. 0.60 0.74

We could leave the analysis there and conclude that AVB was unlucky to be sacked and his replacement has failed to even reach the level of performance that he extracted from an ageing Chelsea team,ripe for change.
However,RDM's detractors have failed to credit him for the additional cup games he has overseen.If we include FA,Carling Cup and Champions League matches in the records of both managers,we not only increase the sample sizes of the games we are looking at,but we also see a large shift in the two success rates.Di Matteo is now the more successful coach and by a significant margin and although his record now contains relatively easy games against Birmingham and Leicester,these are counterbalanced by two games against Barcelona.

We can continue this theme of strength of opponent by returning to only EPL games and once we correct for opponent strength even the argument that AVB outperformed his replacement in EPL matches begins to look much less secure.The average league position of Chelsea's opponents at the time when the game was played when AVB was selecting the side was 11.5,by contrast RDiM's Chelsea faced sides with an average league status of just over 9th.So latterly Chelsea have gained less points per game,but they have on average faced stronger opposition.

We can attempt to quantify this effect by devising match odds from 30 game rolling averages for each team in all of Chelsea's EPL league games played so far this year and compare the expected results against the actual results for the reign of each manager.If we do this we shouldn't be surprised to see that The Blues have underperformed all season,but this declining EPL track record was slightly more pronounced when AVB was in charge than when RDiM was selecting the side once opponent strength was accounted for.So under a system that takes into account who Chelsea played,RDiM is now also the more successful Premiership coach as well as bettering AVB overall.However,...............

Chelsea's EPL Record Corrected for Opponent Strength.

Chelsea Performance. Andre Expected. Andre Actual % Under
% Under
Points Per Game in Premiership. 2.11 1.70 19.4 1.84 1.50 18.5
Success Rate in Premiership. 0.74 0.61 17.6 0.65 0.55 15.4

........this post shouldn't be taken as a declaration that AVB was inferior to RDiM because we simply don't have enough data points to be sure.The 27 EPL games for which the former was in charge is barely enough to gain a decent estimate of a team's worth and the ten game league stint enjoyed so far by his replacement is of insufficient size to make any definite statements.But it should demonstrate that points per game averages are no more than rough estimates,even over dozens of games and are often completely misleading as a means of presenting an opinion about a team or manager.The two men's points per game average alone will tell us very little about their relative quality.Indeed if Chelsea beat Blackburn at the Bridge on Sunday,DiM's average will approach that of his predecessor partly because he has been in charge for so few league games.

At the very least a rudimentary correction for opponent strength needs to be made and even then any conclusions should be tentative rather than definitive.                

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