A major analysis of referee’s decisions in the Premier League has shown that officials are around 15% more likely to book foreign players who are from the same background as the most sizable ethnic minority groups in the UK.

The analysis by researchers from the Universities of Birmingham, Cambridge and Oxford used the extensive in-match dataset collected by OPTA Sportsdata for the 2006-07 and 2007-08 seasons covering 760 games in total.

This included time-stamped and spatial data on every single action (e.g. passes, tackles, crosses, dribblings, etc.) in each of the matches, as well as information about individual players including their position, age, height and the type of game (e.g. local derby). Using such detailed data allowed the researchers to rule out the possibility that the higher level of bookings reflects a more aggressive style of play.

Instead they conclude these patterns point to the presence of what psychologists dub "implicit discrimination". This is the unconscious association between members of a social group and a negative attribute.

Dr James Reade from the University of Birmingham explains: “The results of the analysis were very clear that referees are more like to book foreign players who are from the same background as the most sizable minority groups in the UK.

We analysed a huge range of factors taking into account the player’s style, age and position as well as data about individual matches. This means we are confident this is not the product of playing style but other factors.

We do not believe that this is deliberate discrimination on behalf of referees indeed they are probably completely unaware that this issue exists. Instead this comes from the unconscious mental association between members of a social group and a negative attribute.”

The researchers were able to show that this is implicit discrimination, instead of a conscious form of discrimination based on, e.g., referees dislike for a certain group of players, by performing a detailed analysis of the types of offences being punished, where on the pitch offences occurred and the state of the game at the time. Two issues seemed to be particularly important:

The level of discrimination increased the more rushed the referee was in taking a decision, which happens when players are trying to put the ball back in play quickly to keep the game moving

The level of discrimination also increases when there is more room for debate on a decision. So discrimination was more evident in yellow cards given for fouls (which are always debatable) as opposed to those for excessive celebration or referee abuse which are not

Dr. Edoardo Gallo from the University of Cambridge adds:  “Psychologists have shown that implicit discrimination is the by-product of very rapid, unconscious cognitive processes that replace deliberate, conscious decision-making when there is no time to make a decision or it takes too much effort due to the ambiguity and complexity of the situation.

It is not surprising that referees resort to these rapid, unconscious decision-making processes during high paced Premier League games where some debatable decisions cannot even be resolved by expert pundits sitting in Match of the Day’s comfortable studio..

The results of this research, which looked at two complete Premiership seasons, are clear and something we would like football authorities to consider: referees are top professionals that are doing their best, but they are humans and need to receive adequate support to avoid the pitfalls of fast decision-making in a complex setting.”

The paper: Punishing the Foreigner: Implicit Discrimination in the Premier League Based on Oppositional

Identity is available on the University of Birmingham website, and is forthcoming in the Oxford Bulletin of Economics and Statistics.