MatterOfStats Founding Fellow, Greg, posed an interesting question to me last week: in which quarter is Home Ground Advantage (HGA) greatest?
To answer this question I've assembled the data for every home-and-away game played in every season from 1897 to the end of Round 17 of 2014. Mostly, I've treated as the home team in any contest the AFL-designated home team, though there might be a handful of games in more-recent seasons where I've flipped the team's statuses in cases where it made sense to do so.
I've defined HGA in two ways:
- The excess in the average points scored by the home team relative to the away team
- The excess in the average points scored by the home team relative to the away team expressed as a percentage of the average total points scored in a game (for the relevant season or era)
Before we get into a quarter-by-quarter analysis, let's first just look at average HGA per game for every season.
The colour-coding reflects the different Total Scoring Eras that I identified is an earlier blog.
We see that HGA has generally tracked in the 5 to 10 point range throughout the history of VFL/AFL, with an overall downwards trend in recent seasons.
Expressed as a percentage of the average total score in games during the season, HGA has tracked mostly in the 2.5% to 7.5% range and still shows a downward trend in the most modern era.
It's interesting to note that there has never been a full season for which HGA has been zero or negative.
There have though been whole quarters of entire seasons in which HGA has been negative, for example in 2001 when home teams were actually outscored by away teams in final terms.
The pattern of HGA by Quarter from season to season is remarkably inconsistent. So far this season, for example, HGA has been largest in Quarter 3, whereas in 2012 and 2013 it was largest in Quarter 1. In 2011, Quarter 4 was when HGA was largest.
Focussing our attention on only the two most-recent eras, spanning 1976 to 2014, helps make this variability even more apparent.
Another notable feature that this view highlights is the apparent constraint on the size of HGA in any single quarter: about 5 points seems to be the natural limit.
Aggregating the data for each era highlights longer term patterns in HGA by quarter.
Quarter 4 emerges as the quarter where HGA is highest in six eras, although four of those come in the first five eras through 1947, and only two have come in the four eras since. The last two eras have been characterised by relatively similar HGAs for every quarter.
Very similar patterns emerge when we look at HGAs as percentages of Total Scoring, but what we also see in this view is the overall trend towards smaller HGAs by quarter when measured in this way, for about the last five eras. During that period only one HGA for a quarter has exceeded 6% of the average Total Score in a game from the relevant era.
No matter how you cut the data, Home Ground Advantage has been a consistent feature in VFL/AFL football, generally worth about 5 to 10 points per game and 1 to 3 points per quarter.
No particular quarter has been the one in which HGA has been greatest, and this is especially true for games played in the most recent eras.