Home advantage in the Premier League as time elapses
What is playing at home worth in the Premier League? Does it change as time elapses during a match? At what point in a match does it begin to seriously diminish? Today Andrew looks at how long home advantage lasts in the English Premier League.
Over the last year or so, a catch word around the football world has been 'soccer analytics', the task of breaking football down to its core mechanisms, assessing club performance, working out why some clubs do well and why others don't.
Some analysts are professionals, deconstructing football from all angles (at times to a banal degree). While others do it for the love of the game..........and/or numbers.
One of my favourite analysts is Ford Bohrmann. I stumbled across his work on Twitter. On his site, Soccer Statistically, Ford shares his perspective on football stats and gives his readers some intriguing visual breakdowns.
One tool he has developed is his Outcome Probability Calculator. Here he has used 10 seasons of Premier League data and created a cool applet where users can find the probability of a fulltime result depending upon the goal difference at a particular time in the match.
As home field advantage is something that interests me, I decided to use Ford's calculator to assess home field advantage as a match progresses.
And here's the result.
Home advantage with scores tied
Firstly I decided to look at home advantage as time elapses with the scores locked. The chart below shows how home advantage decays throughout a match as we head towards fulltime.
As per Ford's calculator, at kickoff, home teams have won 49% of matches played in the Premier League over the last 10 seasons, with away clubs winning 28%, giving home clubs a proportional advantage of 1.75 over their visitors of winning the match.
With scores tied, we can see that the likelihood of the home club winning deteriorate proportional to the probability of the away club winning as time elapses. And when scores are tied post the 80th minute, we can see home advantage drop significantly to the point where as we enter injury time, the likelihood of the home club breaking the deadlock, though slim is virtually equal to that of the visitors.
Let's look at the issue in pure terms. The chart above displays the difference in winning probabililty as time elapses between home clubs and away clubs when scores are tied. We begin with home clubs having a 21% greater probability of winning the match as we kickoff, a 15% greater chance at halftime when scores are tied with both home and away clubs having equal chance as we enter injury time. We can also see that the difference between the home club winning and away club winning steadily diminishes throughout the 1st half and picks up pace as we go beyond the 70th minute.
The task of quantifying home field advantage is a difficult one. We know it exists. We can see it play out each and every weekend. And quantifying home field advantage as time elapses, although a more complex task is one that would be well worth the endevour, not only in terms of in-play betting implications but similarly for tactial implementation for any serious manager.
Although we've taken quite a simple and limited approach to assessing such advantage as the 90 minutes of a football match elapse, it would be great to see serious football analysts take up the task and investigate the phenomenon of home field advantage to a much deeper degree.