By Daragh O'Leary

​Expected goals (xGs) have become one of the most commonly used metrics in football. A X/Twitter page called The xG Philosophy has gained over 460K followers by simply tweeting the xG score lines of football matches. The xG statistic is a variable which expresses the probability that a chance in a football match will be converted into a goal. It’s value ranges from 0 to 1 and it can be interpreted as follows: A chance which generates an xG value of 0.6 is a chance which should result in a goal roughly 60% of the time.

Personally, I find myself somewhat agnostic towards xG statistics. While I do think it has some kind of value, I am amazed at just how popular the xG statistic has become. My major issue with the metric is that I think it’s misused a lot of the time. A result of this misuse is that a lot of people seem to misunderstand what the statistic means.
           
As a quantitative economist, I have always been of the opinion that there is nothing wrong with statistics – they’re just numbers. Issues only arise when with statistics when they are used to try and explain something which they don’t measure perfectly. Put more simply, using statistics isn’t an issue, misusing them is. I’ll now outline a few of the ways I think we could improve our use and understanding of the xG stat.

Stop aggregating xG
An xG is simply a number which attempts to quantify the likelihood that a single chance in a game will lead to a goal. If a team is awarded a penalty kick for example, that penalty generates an xG value of 0.76 because roughly 76% of penalties are scored. A long range shot from outside the box may have a lower xG value of only 0.1 indicating there is only a 10% chance that that incident will lead to a goal. With this being the case, I am amazed that people feel it is appropriate to aggregate the xG of a team or a player after a match.

Consider for example a match where Team A are awarded a penalty and have an xG of 0.76 at full time. Then presume that their opponents, Team B, take 8 long range shots which each have a 10% likelihood of being scored. At the end of the match both team’s xG would be 0.76 to 0.8 making it seem as if both teams created chances of a similar quality. In reality, one team had one very good opportunity to score (a penalty) while the other team had multiple poor goal scoring opportunities which they were very unlikely to ever score from.

Accordingly, my suggestion for the xG stat would be to stop presenting it as an aggregate statistic and instead use it to report the number of chances a team created which had a high likelihood of success. In the example above it would be better to report that that Team A had one goal scoring opportunity which had an xG of over 0.75 while Team B created zero goal scoring opportunities which had an xG of more than 0.1. This more accurately showcases the likelihood which each team had of scoring during the game.

xGs aren’t uniform – player differentials
Finally, there needs to be a greater understanding that not all chances are as likely to be converted by all players. Some players are more clinical than others. Ivan Toney for example has taken 29 penalties in his career and converted all but 2 of them. Meaning he currently has a conversion rate of roughly 0.93% from the spot. Why then when Ivan Toney takes a penalty should there be an xG value of 0.76 recorded for it?

This isn’t something which can really be fixed about xG. The value of xG is that it can indicate the quality of chances for different teams across different games, so we need to report it in a standardised manner. However, it is worth noting that chances which have the same xG value are not necessarily going to be converted similarly by different players. For example, if Ivan Toney took 10 penalties and scored them all, most people wouldn’t be too surprised because he’s known for being an excellent penalty taker. However, according to the xG metric, scoring 10 goals from 10 penalties (xG=7.6) would mean he has scored 2.4 goals more than he should have. In reality, he’s just doing what most people would expect of him.

By David Butler

I regularly teach students about the classic screening models in Economics. For the uninitiated, this is when the abilities of individuals are assessed by an uninformed person before a trade is completed. I use all the classic examples; job interviews, credit rating checks and medicals for sport stars prior to transfer - these activities all attempt to screen out the lemons! Nobody wants to buy a dud and they realise the selling side may be privy to sensitive information they wish to keep secret.

This leads us to the recent transfer of Sandro Tonali from AC Milan to Newcastle. It struck me as odd that AC Milan would sell one of the best defensive midfielders in Europe at the age of 22.  It has now come to light that the player was making bets on AC Milan matches during his time with the Serie A side and faces a 10 month ban from football. This could be up to a three-year suspension under FIFA rules if the player chooses not to cooperate.

Did AC Milan engage in opportunistic behaviour? It is plausible that the selling club knew about this behaviour and benefited. While Newcastle likely did a professional job screening for all the potential lower limb problems and underlying physical issues, perhaps their screening failed elsewhere. 

By John Considine

Last week I looked at the number of women referees who took charge of the elite level of women's Gaelic games.  Specifically, I used the senior inter-county championships as listed on the websites of the relevant organisations.  Women are underrepresented by almost any criteria.  All the players are female.  Half the population of Ireland is female.  I guess that the majority of the members of the sporting organisations are female.  Yet, as the pie charts below show, women are a small share of the referees for these elite games.

It may not be easy to increase the representation.  Maybe the two football referees and the one camogie referee in the above numbers could be given more games.  Or maybe more female referees could be used.

A bigger problem is getting referees of any classification.  Like many others, I'm well able to question a referee's decisions but I admire anyone who does the job.  Yet, I would be slow to encourage family or friends to undertake the task.  Only last weekend, another physical confrontation with a referee in Gaelic games made the headlines (here).

Maybe we should treat referees like the other service providers in Gaelic game, e.g. pay them the same rates as the service providers such as Strength & Conditioning coaches.  Lip service about respect only goes so far.  Even as an economist I realise that there are limits to what money can buy.  The philosopher Michael Sandel, in his book What Money Can't Buy and associated YouTube clips, has some nice examples where payment can show a lack of respect.  Imagine a friend invites you to their parents' house for dinner at Christmas.  Then, after a wonderful time, you pull out your wallet and ask "how much do I owe you?"  I don't think any referee would be offended by getting the same amount of money as the service providers to the competing teams.

By Robbie Butler

At the ESEA Conference recently held in Cork, I spoke to several journal editors about the challenges they had in recruiting reviewers. I was reminded of our conversations this morning as I completed my 50th referee report since 2017. The data is presented to the right.

I thought this number was high, until at a conference in Belfast last month where a delegate told me they do roughly two referee reports per week! That’s more than 100 a year.

When I spoke to the editors at our conference about getting reviewers, they told me that many simply ignore emails while others just decline.

I have declined to review, when invited, less than 5% of the time. The reasons for not reviewing were due to timing constraints (editor wanted a 7-day review), lack of expertise in the area and unreasonable administration requests when asked to review.

I find it an honour to review work. It makes you part of the community of scholars and helps build relationships with others. It also builds your profile and standing in an area. You learn a lot from reading papers that you might not ordinarily read.

Surprisingly to me at least, editors told me rejection of invitations to review was acutely true of younger academics. I would encourage anyone at the early stage of their career to review as often as you can – assuming you have the expertise – as it can only help in the journey ahead. 

By David Butler

Last week the 2023 Salary Guide for the MLS was released. This is some of the best data we have on salaries in football as it comes directly from the players association. The data contains salary information for all MLS players under contract as of September 15, 2023. Messi is earning $20,446,667.00 in Guaranteed Compensation. While there is still a great degree of inequality in pay, there are now 114 MLS players earning $1m or higher in Guaranteed Compensation.

The Lorenz curve below is a useful way to visually represent the income (in)equality across the 2023 salaries. The graph plots the relationship between the percentage of the population of players (924) according to their guaranteed compensation and cumulative income. The diagonal line represents perfect equality in income and the curve offers visual insight on how far away from this equal distribution the actual salary distribution is - the further the curve is beneath the straight diagonal line, the higher the level of inequality.

The Gini coefficient is 0.6 suggesting there is a substantial gap in earnings. This is a measure of dispersion and is the ratio of the area between the perfect equality line and the curve. The higher the Gini coefficient (0-1), the more unequal the distribution is. In a simply sense,  this figure tells us that a bigger share of the total budget is in the hands of a relatively small group of players.

Does it matter?  It may for individual franchises. There is evidence in sport that teams with lower levels of wage inequality can achieve higher win rates. Maybe paying Messi so much more than his colleagues is not the best idea?

By Robbie Butler

One of the many unintended consequences of the Covid-19 outbreak was to hasten the movement of many things from hardcopy/in-person to digital/online. Money is one such example. Cash is a dying commodity with debit card, smart phones and sometimes digital watches used to pay for goods and services.   

Another casualty of the crisis has been the physical matchday programme. The club I support no longer produces a hardcopy of the programme which instead can be downloaded digitally. This was a decision made after the return of football fans to stadia following the pandemic.

During the week a GAA memorabilia collector bemoaned this transition on local Dario. He argued that this transition was eroding decades of social history which were stored in these programmes. The artefacts not only acted as an official record of a game but also provided information on other things such as economic conditions, business operation (via advertisements) and community notes.

Many collectors of such programmes will argue that the programme was more than just an account of the day but served the common good, acting as a public good of sorts long into the future.

The decision of clubs is understandable. The economic costs of hardcopy production are high. As someone who sold matchday programmes when I was young, it was plain to see how hard it was to equate demand with supply. Often, we would be left when hundreds of copies of unsold programmes. The timeline for production is also very tight. Hardcopies need to be with a printer days in advance.

The marginal cost of a digital programme is close to zero. Digital editions can change in an instant, right up to kick-off time. There is no paper or printing cost.
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It remains to be seen how long the hardcopy will survive in our digital age where “sustainability” is such a ubiquitous word. And while there are gains to digital production, something has been lost. A social and economic history that others will not be able to access as easily in the future. The days of finding old programmes in the attic will be long gone. 

By Robbie Butler

Almost three years ago I explored the Nations League and qualification for European Championship Finals. I posed the question whether it was more advantageous in the long run (qualification) to lose some games. The piece can be found here.

I still struggle with the competition structure and how qualification can happen. It is dependent upon so many factors - not simply where one finishes in their group - but where others finish in different groups and how these countries performed in the 2022/23 Nations League.

From the perspective of the Republic of Ireland, given their campaign so far, and that of the Netherlands and Greece, it now appears to be the case that the Irish will be better off losing their final group game in Amsterdam against the Dutch. 

This would mean that the chances of more than seven nations finishing above Ireland in the Nations League rankings, and not advancing to Euro 2024 through automatic group qualification are lower, should the Dutch beat Ireland. Greece are ranked below Ireland and already have a play-off spot confirmed thanks to winning their Nations League group. 

Another unintended consequence surely of this incredibly complex qualification system.

By Robbie Butler

In 2022 the sports economics journal space welcomed it's third dedicated entry. Along with field journals Journal of Sports Economics and International Journal of Sport Finance, Elsevier published Sports Economics Review emerged. 

The scope and aims of the journal include "submissions that deal with various economic topics in the sports industry or manuscripts that use sports as a laboratory to study human behavior...[and] is open to different research methodologies that are employed in general interest economic journals, as long as they are relevant to the topic and employed rigorously."

Edited by Alex Krumer (Molde University) and Stefan Szymanski (University of Michigan) the journal is quickly building a very nice back catalog and will publish Volume 4 in December of this year. 

All volumes to date can be found here while the most downloaded papers can be found at the link.

By David Butler

The Luis Dias ghost goal has attracted media attention and placed a lot of pressure on the PGMOL. Was the shocking decision-making bad news for the EPL? Perhaps not when it comes to engagement and viewership.

In a recent paper, we look at what causes fans to tune in when the result of a match is known – we were interested to find out why football fans would watch highlights online when no outcome uncertainty exists.

One covariate in our model to explain highlight views is VAR controversies – we sourced these incidents from Sky Sports and BBC commentary timelines. They were relatively easy to identify.

We find evidence to suggest that VAR incidents stimulate increased viewership on YouTube. Although this effect is only at a 10% level of statistical significance in some models, these contentious deliberations - arising from the use of the technology -  attracted mores streams. 

Maybe it is Spurs and Sky Sports who are the biggest winners from the PGMOL muck up. 

By Robbie Butler

It now appears that the UK-Ireland bid to host Euro 2028 will stand unopposed next Tuesday after Turkey withdrew from the UEFA bidding process.

It will be a big news day here - Budget 2024 and Euro 2028. While the former will directly impact the entire country, the latter's impact will be seen mainly around the leafy, southside of Dublin.

Ever since the UEFA European Championships were started back in 1960 the hosts have been part of the finals. On every occasion, even when just 4 teams played in the Finals (1960-1976), at least two locations were used in the host country.

​The first two Finals in France and Spain used to locations. Italy 1986 expanded this to three but is probably best remembered for the coin toss semi-final victory of the hosts over the Soviet Union. Penalty shoot-outs would arrive as a result. While Euro 2020 changed the traditional format, and move towards city hosts, Euro 2028 seems to be somewhere between this and the upcoming Euro 2024, hosted entirely by Germany.

If the UK-Ireland bid is successful, it will be the first time "host" countries use just one location. 

England will probably have 5-6 stadia in use, but UEFA members Northern Ireland (Belfast), Rep. of Ireland (Dublin), Scotland (Edinburgh) and Wales (Cardiff) will just have one.

It is hardly the country hosting the Euros but rather the city, just like Baku, Budapest, Copenhagen and others in 2020. Nobody suggests Romania hosted Euro 2020. The country can be altered.  Automatic qualification, one of the biggest rewards for hosting, is also not guaranteed at Euro 2028.

It would appear that this is a nice PR exercise between these islands and UEFA members, with England allowing nearby capitals host games. A localized version of Euro 2020 where London played the lead role.

Is "Ireland" hosting Euro 2028? I don't think so. Dublin is the venue some games and maybe Belfast but the rest of the island will look on like every other country.