This is just a very quick follow up to yesterdays post. Call it hedging my bets – but this is an important concept. When calculating home advantage in the qualifiers between teams from the same division it turned out that home teams win 81% of the time (16 games). In Gaelic Football terms 16 games is about a quarter of a season so it does seem relatively big but in reality 16 games is tiny. There are just too many other factors (ignoring home advantage) that could be at play in such a small sample size.

So how accurate is the 81% figure. Well it definitely tells us what happened in the past but can it be used to predict the future? The one big thing that tells me this figure wont stay this high is that when we look at all the studies on home-field advantage across any number of sports we almost never get a figure this high. Could home-advantage be that important in GAA – I can’t see why it would be any different to American football, baseball or Basketball. In fact when we look at League home advantage in each of the 4 divisions separately we don’t get close to these numbers.

There is a concept in statistics called regression towards the mean. In any data set you would expect to see fluctuations. Even if you toss a coin it will not always go Head-Tails-Head-Tails etc… You might get a run of heads and then a run of tails. Getting a run of tails after a run of heads is not unexpected, as such, its just that if you toss a coin for long enough you will eventually end up with 50-50 split. A run of heads or tails is likely just the data regressing toward the mean.

So what has that got to do with home-advantage. Well 80% seems unnaturally high, not unlike a run of heads. So without predicting which matches will go which way, or even if we will see the regression start this weekend, I would expect home advantage % to return to a more normal level. So for any punters, don’t just blindly back the home team this weekend.