Saturday, December 20, 2014

Premier League: who will improve in the second part of the season? Part 2.

In the Part 1I used the shots per goal conceded statistics to figure out which teams may have been (un)lucky in the first 16 games of the season and are expected to improve the defensive record in the remaining games of the season. In this article I will do the same for the offensive side of the game – are there teams that score fewer goals than they should simply because they have been unfortunate?

Thursday, December 18, 2014

Premier League: who will improve in the second part of the season? Part 1.

It often happens that some teams perform better in one half of the season then in the other. Sometimes it is related to injury crises, sometimes it happens due to big winter signings (or losing players), sometimes there is simply a hot (cold) streak, for which it is hard to find a particular reason.

But sometimes it is just being (un)lucky.

What I will try to do in this article is to find an indicator that shows that a team concedes more or less goals than it should. And for that reason I will use a very simple statistics: goals conceded per shots on goal allowed.

It is fair to say that the average number of shots needed to score almost does not fluctuate from season to season: in 2012/13 it was 10,16 shots per goal, in 2013/14 – 9,98; this season it is exactly 10 shots per goal.

Also, nothing indicates that this number has something to do with the quality of defense or overall strength of the team. Here is, for instance, data for 2012/13:

I assume that +/- 1,5 shots per goal is normal fluctuation, while more of that signifies that something is going on. If there exists something systematic that makes a team concede from more/less shots on goal, then it should also translate into next seasons. Let’s look at the season 2013/14 then:

We can see several usual suspects here: Chelsea and West Ham on the positive side; Tottenham and Southampton on the negative. It is improbable that they are simply unlucky for two consecutive season, so it must be something else that makes them concede from more or less shots. What can be that?

1)   The goalkeeper. It is easy to imagine that Petr Cech is responsible for some crucial saves that others would not have done, therefore decreasing the total of goals conceded. But look at the difference: in 2013/14 with 391 shots allowed, Chelsea were expected to concede 39 goals, while they actually conceded 27. Can Cech single-handedly save the third of goals? Were Joe Hart or David de Gea so much worse that they did not come even close to him? It is hard to believe that.

2)   Fearsome defense. How about that for a narrative: Chelsea’s opponents were so hopeless to come close to Chelsea’s goal through Terry and Cahill that they were trying to score from distance, meaning that each shot had a lower probability to result in a goal. No, I don’t like it either.

3)   Style of play. It may have something to do with style of play, something that is not measurable or noticeable.  For instance, Chelsea and West Ham may give opponents more freedom outside the box, encouraging them to shoot from there more often, while Tottenham and Southampton limit opponents’ shooting from distance, but allow more clear-cut opportunities.

Whatever it is, if we look at this season and see that Chelsea, West Ham, Tottenham and Southampton do not go in line with the rest of the league, we will not attribute it to random fluctuations. And here is the data for 16 games of this season:

Since sample size for this season is much smaller, I raised the bar of normal fluctuation to +/- 2, which allows me to make three predictions for the rest of the season.

1. Arsenal are unlucky and will improve defensively.

It is an easy one, because the current statistics is ridiculous. Allowing 4 shots per game less than Stoke, they managed to concede as many goals. Arsenal have been “neutral” in the last two seasons, so it is safe to say it will take more shots to score against them in the future.

2. Manchester City are lucky and will deteriorate defensively.

After 16 games, Manchester City conceded 3 goals less than they should have done from the number of shots they allowed. Being just in the green zone at 12,1 shots per goal, they are actually not very far away from their 2012/13 record (11,6). Last season, however, Manchester City were below average (9,7) suggesting that, unlike Chelsea, they do not possess black magic and will regress closer to the league average.

3. West Bromwich are unlucky and will improve defensively.

Let me rephrase it. West Brom are very unlucky and definitely will improve defensively. It takes less than 6,9 shots to score against them – unless you really hate Ben Foster, it is hard to develop a narrative that would explain it. From 200 shots, they conceded 29 goals, 9 more than they should have. 10th in the league by shots allowed, they are second-bottom by goals conceded – better only than QPR.

You disagree with my predictions? I can bet on them.

In the next article I will conduct a similar analysis on goals scored.

Wednesday, December 17, 2014

Chelsea winning the quadruple is as likely as Liverpool relegating to Championship

After a comfortable win over Derby County in the League Cup quarterfinal, Jose Mourihno and Cesc Fabregas had a little disagreement over their team’s chances to win nothing less than quadruple this season. The Spaniard, probably encouraged by lack of resistance from Championship opposition, said that Chelsea “have all what it takes”, while the manager insisted that “it is impossible”.

What is the true probability of Chelsea winning a quadruple or any other combination of trophies, as of December 17th, 2014? To derive probabilities, I used bookies’ coefficients (if someone has better estimations, which is confirmed by a long record of beating bookies, please let me know: not only will I use it for this and similar post, but I also will invest money in your strategy).

Monday, December 15, 2014

How much success can money buy in football?

Massive inflow of investment into English football prompts us to consider question "Does money buy glory?" more often. Most of supporters would love "No" to be the answer - in fact, as a hope, we get some fairy-tail results from cup competitions, like Wigan beating Manchester City in the FA Cup in two consecutive years. Yet, quite sadly, it seems that the examples of money-not-buying-glory are mostly limited to cups and are a natural result of big number of one-game encounters, where a 1-in-10 chance of underdog beating favorite will provide a couple of very unexpected results every season.

This article presents relationship between wage bill and performance of Premier League teams in 21st century - starting with the season 2000/01 and until 2012/13 (the latest data available). Just in case you don't want to go through the whole article (full of numbers, I must warn), the bottom-line is the following: money may not guarantee the success, but it buys most of it - just above two-thirds, to be precise.