EPL REFEREE REVIEW 2012: NUMBERS SHOWING BIAS? « Untold Arsenal: Arsenal News. Supporting the Lord Wenger; coach of the decade

The previous article in this series can be read here

By DogFace and Walter Broeckx

Untold Arsenal has a team of qualified referees who have reviewed more than 40% of the EPL games from last season. The reviews themselves were based on full match video footage with the advantage of video technology features such as slow motion and pause.

By reviewing those 155 games we have made a database of more than 7000 decisions that have been judged by our panel of dedicated and qualified referees.

The numbers you will see are based on those decisions and those reviewed games.

Is there any bias?

People who have been following football a bit know that at a certain moment during last season Mike Riley, head of the PGMOL came out saying : there is no bias amongst refs in the EPL. We just had to take his word for it. But even before Riley had spoken we were determined to see if there is a kind of bias. Or worse…are there a few different kinds of bias in the EPL?

And so, to attempt to establish this, we need to look at the numbers of the calls where refs didn’t follow the rules. There will of course be genuine mistakes – but these should ‘even out’; what we look at is the bigger picture and that will be shown as a conscious or unconscious inconsistency in the number of errors made… and you can see this in the next graphic as we take on the fact that pundits tell us that no form of bias exists and it all ‘evens out’ over the course of the season.

Summary of bias – all teams/all referees:

Again in this graphic the “medium” decisions= yellow cards, the “high” decisions= red cards, penalties and goals and the “low” decisions are the other decisions the little fouls somewhere on the pitch.

Our numbers clearly show that when you are playing at home you are likely to get some 10.077 weighted points value in your favour. This is the total decisions included the weight system we use to determine the weight to each decisions. This number is based on the errors a referee has made during the season for all home teams in those 155 games we reviewed. But when you are away from home you will only get some 7.458 wrong weighted points value in your favour – this gives us an overall average weighted Bias advantage of 2.619 weighted points per game – which translates as 1.826 incorrect decisions in your favour. This is also borne out in the average Points Per Game for Home and away teams with the home teams taking an average of 0.677 EPL points per game more that the away teams in the games we reviewed.

This means that there is a difference, when it comes to the ratio of referee mistakes, of around 57.468% in the home teams favour – this is a swing of 14.936%, in judgement, depending on being the home or away team.

I can imagine some of you saying: but this is normal. But I don’t think it is normal, and in this I agree with Mike Riley because he said that there is no bias so there should be no difference between playing at home or away. But there clearly is a difference as our numbers show. In a further stage we will try to find out if we can see patterns  when we look at the individual teams and try to find out if some teams go over those numbers or some teams go below those numbers.

But what you surely must remember is that the ref clearly feels the pressure of the home crowd and that this pressure reflects in their decision making.

The next thing we can deduct from this is where the old platitude “it all evens out” comes from. Because over the course of an entire season for ALL teams it can be said statistically to “ALL EVENS OUT”. Of course it does, viewed as a whole this calculation is zero-sum; just take a look at the above graph at the Bias points for the ‘Combined’ totals.

Experts can look you in the eye and tell you it all evens out at the end of the day and this is true when you look at the league… but this may NOT be true when it is broken down regionally or, indeed, on a team-by-team or referee by referee basis.

To explain – whenever a referee makes a mistake this decision goes in favour of one team and there is always another team who is suffering from the decision. So if there are 100 wrong calls in a season there will be 100 teams being lucky and 100 being unlucky. And so you could say that it [luck] all evens out.

Of course when you are supporter of a team you don’t care about the global fact that it evens out. What you want to know is: does it even out for my team? Because if your team is involved in 100 wrong calls during a season and you are on the bad end 99 times you will not find it a big consolation that from a league point of view it evens out at the end. No you will and rightfully so, say that your team has been hard done by the refs. And that it is an utter disgrace. And you will not believe the pundits when they come up with the old apology: it evens out at the end of the season.

We at Untold look a little deeper than this and seek not only to scratch the surface of that platitude but also to smash through the shell and lay its contents bare… We will try to show with the numbers of each team; if this was the case for each team during the season. And you will be able to see how much the difference there is between the average home and away bias and the home and away bias of your own team. We will attempt to discover if the EPL egg is healthy or rotten.

In the next graphic we will give you an overview of how the incorrect calls have had their influence on the different teams. this is not about home or away, no this is about the total influence of incorrect calls on each team.

In this graphic you see the decisions in favour of a team are situated above the zero line. The decisions against a team are below the zero mark.

At the centre of the graphics is the zero-line. And if all the mistakes would even out as is being said by the pundits then all the teams would have the same height in the different incorrect calls. Above the zero line is the decisions in favour of the said team and below the zero line are the decisions going against said team.

It should have the same height in total and in the different types of decisions.  Well it is clear to see that it doesn’t even out when you look at a team to team basic.

And we even see a few strange results in this but we will dig deeper in that when we talk of the individual teams.  But just want to point at Stoke who seems to be a team that gets both hot and cold from the refs last season.

It is interesting to note that with the weighting applied (big calls worth more than small calls) the order of bias changes. Also it should be noted that teams such as QPR have only had 8 matches reviewed and, in their case, 2 of these matches involved a couple of real stinkers (or outliers) from Mike Dean Vs Arsenal – so their position in this table is perhaps not representative of their entire season.

We will focus on each individual team more in the following articles but if ever someone tells you that it does even out just link him to this article and he will have to admit that it does not even out.  NOT on a team basis. And that team basis is the only important thing for any team supporter.

The final conclusion for this article: There is a home and away bias and we have this proven by the numbers. I hope Mike Riley reads it and admits being wrong when he said there is no bias in football.

The old platitude that “it evens out’ is not true.  The only way it evens out is when you look at the league in a whole.  So whenever someone tells you it evens out you ask him to prove it on a team to team basis.  We proved it doesn’t even out with our numbers. They only have … just what do they have to prove what they say?

Next article in this series: Digging deeper : is there a regional  bias to be found?