Does this have anything to do with the GAA itself?
No. This is entirely a pursuit of fun – though if the GAA ever wanted to adopt it to introduce some sort of seeding/ranking system, they’d be welcome to do so.
So who does run it then?
Gavan Reilly (hello!). I’m a journalist – currently the political correspondent at Today FM – with a grá for numbers. And for gaelic games, evidently.
What’s the rating all about?
Each team – in both hurling and football – is given a rating which reflects its performance against other teams. This rating takes into account the quality of the teams they’ve played against, how easily they’ve won/badly they’ve been beaten, and the importance of the fixture concerned.
How does it work?
The rating changes after every match a team plays – they will gain points if they win, and drop points if they lose. As we’ve already said, that number of points will depend on the quality of the opposition, the circumstances of the match and the final scoreline.
The system is technically called an ‘Elo model’ – it’s based on the system originally created to rank chess players. Similar systems are used to rank players or teams in other sports – and, notoriously, to rank the attractiveness of female students at Harvard University in 2004.
I’ve written a Calculations page which explains the mathematical basis for how the whole thing works, if you want more detail.
How many games does the system take into account?
Excluding games in pre-season competitions like the O’Byrne or Walsh Cups, the system currently includes every game played in the National Leagues, provincial and All-Ireland championships (including the secondary hurling competitions) since the beginning of 2009 (for hurling) or 2010 (for football).
In time, it’s hoped to build an archive so extensive that it literally includes every competitive intercounty match ever – but building a comprehensive record of those games will take a long time, if it’s even possible. Certainly the results archive at Hogan Stand includes every competitive inter-county match since the 2001 Championship and in time, those games will be added to the database to further refine the ratings.
However, the relatively small pool of games is still enough to make sure the ratings reflects the current strength of every team: Elo systems are designed so that every team’s rating is reliable after around 30 games. Since 2010, every football team has played at least 45 games between football and championship, and likewise every hurling team has played at least 42 games since the beginning of 2009.
In time, if every single match was included in a single database, it might be possible to compare teams across time – and judge how the current All-Ireland championships compare to the best of all time.
Is the whole thing mathematically based?
Pretty much. There are a couple of parts of the system which depend on human discretion – for example, the decision to rank All-Ireland series games as being twice as important as back-door matches, or almost three times more important than League games – but once those values are taken as a given, the rest all works itself out.
There’s only one area in which we’ve taken some executive decisions: you can’t start off by giving every team the same result, because a team with a 50-50 record in Division 4 ends up having the same rating as one with a 50-50 record in Division 1.
Therefore, every team’s “opening” rating is based on the division of the National League that it began that year in. Division 1 teams are given a higher rating than those in Division 2, who are higher than those in Division 3, and so on. After that, the ratings are entirely automated, based on the results of each match they play.
I have more questions…