Why Goal Difference is crucial to Premier League survival

The relegation battle in the Premiership has become increasingly intense. As the season progresses and Manchester United seemingly stumbling towards the title pursued by an equally reeling competition, the bottom of the table proves now to be the more intriguing are of the English top flight. This season sees the most intense dogfight to avoid the drop for many years.

It seems no-one in the bottom half of the table is immune, let alone safe. Before the weekend’s win against a Wigan outfit seeminly every bit mid-table Championship calibre, Sunderland had dropped like an action-movie elevator from potential European combatant to also-ran. Blackpool‘s astonishing start to the season came undone at exactly the same time as Charlie Adam’s Liverpool move was rejected. West Ham remain as consistent as the March weather. On the other hand, Wolves have proved the most plucky of all the teams in the relegation zone yet still prop up the table, hit hard by injury to target-man Kevin Doyle.

What confuses this situation more than in years past is that there are no “certainties” for the drop. Last year Portsmouth failed to break twenty points (thanks among other things to a nine-point deduction for going into administration) and in 2008, Derby County broke Sunderland’s record from 2006 for the fewest points in a season. This year, no such luck: the bottom nine clubs sit within one “six-pointer” of the drop zone.

When comparing this season to the previous decade, the only real precedents for such a tight battle was in 2003, 2007 and 2008, where – aside from the three in the relegation zone – five other clubs finished within six points of the drop. In all cases, however, one club was cut adrift much earlier in the season: in 2003 it was Sunderland, 2007 Watford and 2008 the hapless Derby County. Generally (60% over the last ten years), one club is mathematically relegated much sooner in the season than their compatriots. With only four (or five) matches remaining in this EPL season, there is no such bunny.

As always, the complicating factor in the relegation battle is Goal Difference. Goal difference has been known to be crucial – just ask Fulham fans, who in 2008 saw their club survive thanks only to a GD 3 superior to that of relegated Reading’s. Interestingly, while it’s mentioned often and loudly, that’s one of only two times since the turn of the twenty-first century that a club has avoided relegation by virtue of goal difference. The other was the year before, when a David Unsworth penalty against his former club Sheffield United lifted the Latics out of the drop zone at the expense of the Blades.

Another trend over the decade has been that as more teams are involved in a relegation battle, a greater impact is seen in goal difference over the course of a season. For example, in the years where eight clubs each year finished the season within six points of relegation (2003, 2007 and 2008) – or one crucial win against a fellow straggler – the average goal difference of any threatened clubs was much lower. The same is true in 2011, where nine clubs are still classified “in danger”.

Excepting Derby County in 2008 (who finished the season with 11 points and an all time goal difference record of -69), it’s easy to see that the average Goal Difference of relegation-threatened clubs decreases as the number of clubs increases.

Derby County are excluded because they are a statistical outlier – their season-long goal difference of -69 a whole 57% worse than any club’s during the past seven years – the next worst club in Goal Difference was 2003’s Sunderland squad, with -44. Since they lost almost every game (season record 1-8-29) we can assume everyone took points off them. This assumption may not necessarily be correct, but statistically speaking, it is safe.

As you can see, the tighter a relegation battle gets, the tighter clubs tend to become – with the possible exception of Ian Holloway’s Blackpool. If more club become involved in a relegation battle, it leads to lower average goal differences across those threatened teams. This season has produced another statistical anomaly which is interesting (but not very interesting) – Mark Hughes’ Fulham join Leeds United’s 2003 squad as the only “threatened” club in the last decade to boast a positive goal difference (+1).

It stands to reason that with an increased number of threatened clubs that average goal difference is reduced. If more clubs are involved in the Relegation battle, then that means for an even competition. An even competition means for even scores across a week-to-week basis and no matter if this Premier League has not been one of “vintage” calibre, it certainly has gone nearly unparalleled for intrigue and competition. In days past, the magic total of 40 points has been suggested to be a minimum safe distance. Only once has a club been relegated who had scored above forty points: West Ham, who were desperately unlucky to go down in 2003 with a record points tally.

Therefore, we can say safely with approximately 10% of the season still to play, the 2010-11 average Goal Difference figures are going to be amongst the lowest of the past ten years. If we extrapolate the figures as they stand now, it could mean an average goal difference as low as -16.85 for all threatened clubs over the course of the entire season. If we use Goal Difference as a marker of how intense a relegation battle is, then this relegation battle is statistically slightly (5%) more intense than than the previous most intense fight in 2008 involving Birmingham, Reading, Fulham and Bolton. Only this year, there’s no Derby County – there are no (relatively) easy points.

For more analysis and opinion, shoot across to Matthew Wood’s blog, Balanced Sports.