Monday, January 18, 2010

EPL Halftime Report (long)

I meant to do this last week, but better late than never as they say.

Most Impressive

I suppose it's Chelsea. The blues are three clear in points, one ahead of Manchester United but with a match in hand, and two goals better in differential than Arsenal, who sit second in that category. I'm not sure if others share it but the feeling I have from watching the league is that the top clubs are less dominant this year than in the last few seasons. Just glancing at the table though the opposite appears to be true. Chelsea are on pace for a goal differential of around 60 this year, Arsenal a few less and Man United at around 50. Over the last several seasons the club with the best goal differential has had somewhere between 50 and 60 more goals than their opponents. It looks like the big clubs are cruising along just fine.

Going forward Chelsea's pace will likely slow down due to the knee injury suffered by Michael Essien. Essien is in my view not only the best and most important player at Chelsea, but he is probably the best player in the league. Looking at the season thus far, he has played in 14 of Chelsea's 21 Premier League matches. While the sample sizes of 14 and 7 are very small, comparing the blues' results with and without him in the lineup gives interesting results. When he played, Chelsea outscored their opponents by 1.79 goals per match. When he didn't, they only scored an average of 1.29 more than their opponents. 1.29 would be behind both Arsenal (1.52) and Manchester United (1.36). The most important team stat is shots-on-target differential (SOTD). In the matches where Essien played, Chelsea averaged 11.3 shots-on-target and 4.2 shots-on-target against for a SOTD of 7.1 per match. When he didn't play they slipped to 7.0 shots-on-target and 2.9 for their opponents for an average difference of 4.1. So when he played they were about half a goal and 3 shots on target better than when he didn't. Adjusting for the strength of opponents gave similar results. It'll be interesting to see how things actually shake out.

Most Disappointing

This just has to be Liverpool. Despite selling Xabi Alonso to Real Madrid in the summer, the reds had high hopes for the season. They finished second last year, with the highest goal differential, and their rivals in Manchester sold off the (second?) biggest star in the game. This season little has gone right and their dreams have certainly been tossed and blown. They find themselves out of the Champions League having picked up only one point against the two decent sides in their group, Fiorentina and Olympique Lyon. They lost to both at Anfield, something the commentators likely will ignore next time and every time in the future that they play at home in the Champions League. They are surely a dog to make it into Europe at all this year as Spurs, Man City and Villa all look pretty good and there are only two spots going to those four. It's hard to see Rafa Benitez lasting long; maybe a shakeup is what they need.


Normally I open the luck section of the report by discussing goal differential and how that is turned into points. Something I have admittedly glossed over with other leagues is injuries. For the English Premier League this season injuries have played a very large role for several clubs. Liverpool were without their three best players for several matches as Gerrard and Mascherano each missed 5 and Torres was out for 7. That may seem pretty bad until you consider Arsenal and Manchester United. Essentially every attacking player for the gunners and defensive player for United that most fans have heard of has been out for a significant number of matches. It is quite impressive that both of those clubs have the depth to get results despite all of that. At the top Chelsea had been in relatively good shape, though Essien had missed some matches with a hamstring injury. Unfortunately with a new and likely long-term injury to such an important player, I don't think we can consider them lucky at this point.

Moving on to goal differential, as I've said repeatedly (and will continue to do so) there is a very strong link between goal differential and points over a season and teams doing well or poorly in points compared to their goal differential seems to be only due to luck. This year there is one result that makes me question that a bit, which is Tottenham's 9-1 win over Wigan. The work I've done on goal differential essentially said that big results will, for the most part, even out over the course of a season. So a team's skill level is best represented by their goal differential but they could do well or poorly in close matches due to luck, and that would mean more or fewer league points. In the case of such a big win, I don't think this holds. Going up to a 4 or even 5 goal margin, I think the extra goals are informative; if two teams have otherwise identical records but A beat four different opponents by 4 goals each and B won those same matches by 5 then I think B is most likely better than A. In going from 6, 7 or 8 goals to 9, I don't think the same thing holds. In other words, I think the usual criticism of goal differential - that it overemphasizes big results - isn't all that great in normal circumstances but with that one extreme result it is valid for those two teams.

Looking at the league, the most unlucky team in this regard are Portsmouth. They are at the bottom of the table but are 15th in goal differential per match. Adjusting for schedule and applying the formula from a previous article on goal differential and points, they are running about 5 points below expectation. Next unluckiest are West Ham who are also running about 5 points low. To make matters worse for these clubs, their relegation rivals appear to be fortunate. Wigan rate as the luckiest. They are running at 7.5 above expectation leaving the huge loss to Spurs alone. Converting it into a 6-1 or even a 5-1 loss makes them still the most lucky with over 5 points more than the average team with their (adjusted) goal differential has had. Wolves, Hull, Blackburn and Burnley are all running between 4 and 5 points above expectation according to the model.

Looking near the top of the table there is nothing too extreme. In a shocking twist, Manchester United appear to have been unlucky despite what you might think due to a certain 6th-minute-of-stoppage-time goal and, well, them being Manchester United. Not to worry though, they are only a point or two below where they should be and there is a lot of season left for Alex Ferguson to turn on his luckbox. Chelsea are two or three points below expectation. Arsenal are the top club that is worst off when it comes to this with between 4 and 5 points fewer than they should have according to their goal differential. Combining those two, if the top three had as close to average luck as possible when it comes to goal differential and points then Chelsea would have 50 or 51 points, Arsenal 49 or 50 points and Manchester United 48 or 49 points. That's pretty similar to where we are now.


Another way I measure luck is to compare each club's spot on the table with where they are according to my stats-based model. Unlike the previous section, there is a major skill component. A big reason for this difference is efficiency in front of goal. I'm actually adjusting the model to account for shooting percentage and shooting percentage against and will probably have the new version ready next week.

The first club that jumps out is again Portsmouth. In my stats model they are actually 10th in the league! My first thought when I saw this is that there must be something seriously wrong with the model. That may be true, as I said I'm adjusting it, but there is good reason to think that Pompey are an average team instead of one of the worst. The main argument is that they are 7th best in both shot and shot-on-target differential. I was quite surprised to see that they have taken more shots than their opponents. They are averaging right around 1 more shot and shot-on-target per match than they allow. Given that they have been outscored by 14 goals in 20 matches, it's clear that something is going wrong in front of one or both goals. It is emphatically both. While it is likely the case that the shots they are taking are less dangerous and maybe they are allowing tremendous opportunities for their opponents, the Portsmouth midfielders shouldn't be too happy with their teammates. They are dead last in scoring percentage, putting in an impressively low 13.7% of their shots-on-target*. That is only about 60% of the league average which is 23.2%. At the other end they are only slightly better at second worst. They have allowed their opponents to score on 28.6% of the shots that make it on target. If shooting was about average for both sides in their matches, they would have a goal differential of +4, some 18 goals better than where they are now. To summarize their season thus far, Portsmouth have been put into such bad financial shape that they are struggling to pay their players, they've been both bad and very unlucky in front of goal at both ends and on top of that they are running really bad when it comes to getting league points for a team with their goal differential while their rivals in the relegation battle have been fortunate. Good times.

Another interesting side is Wigan. They are 14th in the table, 12th if you go by points per match to account for the differences in number played. The model puts them 13th best so they are basically right around where they should be if you go by that. They have been nearly as bad as Portsmouth at both ends of the pitch. They are 18th best at converting shots-on-target into goals and the worst at shooting percentage against. Like Portsmouth, they have been some combination of very bad and really unlucky in front of both goals but unlike them Wigan have been fortunate in close matches. That all washes out and it looks like they are about where they should be. If they want to stay up though, they'll need better shooting and goalkeeping from Kirkland.

Stoke City are on the opposite side of the luck wall. They are the worst side in the Premiership when it comes to shot-on-target differential. It's not very close either. Stoke have allowed their opponent to take an average of 3.7 more shots-on-target than they do in a match compared to 2.9 for second-worst Hull. This is hardly new territory for the Potters. Last season they allowed their opponents 155 more shots-on-target than they got. Next worst was Middlesbrough whose opponents took 82 more shots than they did. That is a pretty ridiculous difference and if I only gave you that info you'd be wise to think that Stoke were relegated last year, probably bottom of the table. Both last year and this season thus far the problem has been at the attacking end. Last season Stoke took just 137 shots-on-target and no other team was below 200. This season they are on pace for 134 and the next worst, Hull, will have 181 if they keep up their current rate.

In 2008-2009 Stoke got by due to very good finishing. They had the best shooting percentage in the league. Given the very low number of shots I wonder if this might somehow be part of their strategy - if they are more patient than the other teams and wait for a good scoring opportunity to shoot then that would lead to this pattern. This season they haven't been quite as good but they are 6th best in the league. They are also fourth best at shooting percentage against. Considering that they don't have the talent of the top clubs, these numbers are better than what one would expect from them. I'm sure they have gotten lucky, especially in scoring the number of goals they have the last season and a half on so few shots, but maybe there is something more going on. I personally hope they stay up for at least another couple years because it'll provide more data to see if it is just variance or something deeper.

At the risk of boring the readers that support bigger clubs, I want to also mention Birmingham City. The blues are strong in 8th position, which is better than most would have given them credit for after being newly promoted to the top flight. They are 8th despite being 15th in shot-on-target differential because of luck and apparently good play by their young goalkeeper Joe Hart. They have allowed their opponents a goal on only 13.3% of shots-on-target, the best in the league. In just over half a season he's put up the kind of shot-stopping performance that should get Capello's attention. Maybe not though since David James has been bad in this regard for Portsmouth and is considered the England #1. He also wasn't great last year as Portsmouth finished with the 16th highest shooting percentage against. There is more to keeping than stopping shots, but David James doesn't exactly have a great reputation in those areas.

Moving to the big boys, nothing is far off from expected. The stats model has the top three in the same order the table does right now with Manchester United just a bit better than Arsenal. Chelsea have been good but not great at both ends. They are 7th best at converting shots in to goals and 6th best at preventing their opponents from doing so. Arsenal have the best shooting percentage in the league scoring on 34.4% of their shots-on-target. It seems that Almunia is the player Arsenal fans complain about the most and perhaps that's justified. They are 10th best at shooting percentage against. That's not terrible, but it's easily the worst of the top 3 clubs. Manchester United are 4th best at shooting and have allowed the 5th lowest shooting percentage.

United fans may be interested to know how their performance at the attacking end compares to last season now that they have 100% less Ronaldo. Firstly, they are on pace for 84 or 85 goals this season. Even if they slow down they will likely pass the 68 they scored last season. I should point out that scoring league wide appears to be up. I'm not sure why that is other than that shooting percentages seem higher so maybe the goalies aren't doing as well. Returning to Man U, they are averaging about a shot and a half more per match this season compared to last but they are behind in shots-on-target by that same margin. They are scoring on a much higher percentage of their shots-on-target: 26.3% this year compared to 18.1% last season. Because there is a decent amount of noise in shooting % (expect an article on this shortly), I would say that the data point to a club that is not quite as strong in attack as last season but not far off at all.


It will remain a three-horse race for some time. I'm a bit nervous about this since I was flat out wrong in my prediction that Liverpool would still be around at this stage. Arsenal and Man United are working their way out of the injury problems they've had for much of the season. Chelsea, even without Essien, have looked at least as strong as those two and currently have a cushion. It's tough to see any of the three dropping out of the race. It seems likely that at least two of them will still be fighting the last couple weeks. At this point I think Chelsea remain favorites, though I'm not willing to stick my neck out. Any of them could win it.

Spurs, Man City and Liverpool will fight for the two remaining European spots until the final few weeks of the season. I'm a bit on the fence as far as putting Villa in with this group. I think they're easily the most likely of the four to fall off, though more chaos at Liverpool could prove me wrong there. Right now if I had to pick two I'd take them in the order they are now - Tottenham for the Champions League playoff spot and Man City in the Europa League. Liverpool are far from out of it but they are now four points behind and going the wrong way. I think the reds are a dog to qualify for either competition at this point and are in serious trouble for the Champions League.

Portsmouth will stay up. I'm going to make this my bold pick. While it doesn't seem like a good idea to pick a team that is bottom of the table and in such a bad spot off the pitch, there is a good amount of evidence that suggests that Pompey aren't as bad as their table position. I think at the very least they will climb out of the cellar and fight for another year in the top flight until late in the season. If you disagree with me, and even I might, you aren't alone - Portsmouth are currently the team with the shortest odds in the relegation betting market.

Burnley will be relegated, Bolton will stay up. I'm going to leave the Portsmouth prediction out of it and make Burnley and Bolton my teams to flip. At around the quarter mark of the season, I predicted that Burnley would fall from the middle of the table which has happened. They started out strong with early wins over Manchester United and Everton, but have struggled overall. I like them to drop along with Hull and Wolves. Bolton aren't a great side and I think they will probably be in the fight all season, but they are better than those three.

Finally, I want to follow up on my other prediction form the quarter-time report, which was that West Ham would get out of the relegation zone and be well clear of it by the end of the season. So far so good. I think they'll keep moving up under new ownership. Other than picking Liverpool to stay in the title race, my predictions from then are looking good.

* again I'll say that this might be slightly off due to own goals (likely) not being counted as a shot-on-target. For simplicity of language I ignore this. Due to the rarity of an own goal and that they tend to come on good scoring chances I don't think it changes the implications of the analysis at all.

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