Seasonal scoring trends has been a feature of both the EPL and football league in the past. Goal scoring traditionally started slowly in August, quickly rose to a peak, before falling gradually over the winter months, before a May goals fest. However, in scoring just 74 goals in 39 matches so far, the EPL has set a low scoring precedent.
The average scoring rate in the EPL hovers around 2.5 goals a game, it had averaged 2.64 since 2002 prior to the start of this season. But bouts of lower scoring are also inevitable, especially over relatively small sequences of matches. If you split the EPL since 2002 into weekly blocks of 40 matches, around 1.5% of those 40 match runs produced an average of 2 or fewer goals per game. So on this basis the current run would appear to be certainly rare, but not entirely precluded.
Teams can, fairly predictably, produce low scoring matches over relatively short time frames. The opening group matches of a major tournament, such as the World Cup for example or hugely important one off matches such as FA cup finals, tend to be less goal laden than earlier rounds, in the case of cup ties and later games, in the case of group matches.
However, generally the gap in quality between each side is the major factor in determining how many goals will be scored in a match, especially over league scale time frames. The remaining week four match sees Liverpool travel to Swansea as narrow, 4 tenths of a goal favourites, so you would expect around 2.6 goals to be scored in this fixture, on average. A more of a miss match, along the lines of Palace's visit to Old Trafford would see the total goals line creep just past 3.
It is therefore possible to estimated, based on historical general scoring rates, as well a individual team tendencies, the average number of goals each of the previous 39 games would expect to see and from this information, the range and frequency can be simulated for total goals scored in those 39 games. The most convenient way is to model the sores via a Poisson distribution.
Although it is tempting to lump the first 39 or 40 matches of each season together as a single repeatable trial, there are small differences caused by the slightly different team strengths and match ups thrown up by the fixture list compilers, from one year to the next. The 2013/14 season has seen slightly more closely matched games, based on pre game estimates, than has been the case recently. Therefore, we should expect to see these more frequent, potentially closely fought matches produce less goals per game. However, this effect is unlikely to wholly account for the figures that we have seen.
The relative rarity of so few goals being scored in actual batches of 40 matches is repeated in the simulation for the 2013/14 season to date. The simulations using goal expectancy figures for all sides that would be consistent with figures seen over the recent EPL history, generated a season with 74 goals in the first 39 games once every 550 seasons. While a season that had 74 or fewer goals in the first 39 matches appeared once every 185 campaigns.
So, although not precluded from occurring under the kind of Premiership football we have witnessed over recent seasons, the first 39 matches in 2013/14 are extreme outliers.
We've touched briefly on matches where sides capable of producing games with "normal" goal totals can tactically adapt, possibly through fear of losing, to produce much lower scoring games, such as the opening group matches of a tournament. So perhaps other factors, such as these are present in the 2013/14 Premiership, other than the natural random variation within small sample sizes.
Five clubs do have new managers and one, Mourinho at Chelsea, consistently presided over low scoring matches in his previous stint at the club, under a policy that coveted defensive strength. And as in most sports, defence is more readily organised and excelled at than is creative attacking play. Numerous other managers are also relative newcomers or are now managing in an elevated arena compared to the Championship.
Secondly, almost half of last season's top twenty Premiership scorers have barely kicked a ball in anger, so far. Some, such as Bale and Tevez are no longer Premiership players, while prolific scorers, such as Ba, Lukaku, Suarez and Defoe are yet to start a game. Also, depending on source, shots are currently hitting the target with nearly 40% less regularity, compared to historical levels.
Overall, every team, with the exception of the surprisingly good, Arsenal and the predictably chaotic, Sunderland have been involved in matches that have seen their total match goals come in below the expectation predicted by an, until now, robust Poisson based modelling approach.
It is easy to weave narrative when presented with unusual outcomes. The goal glut at the start of 2011/12 didn't continue, although the chances of it appearing, with little change in scoring intent, was a much more substantial 18% compared to the present paltry 0.5% for our current drought. For once sample size and random variation doesn't appear to Bale out those looking for a mundane explanation, although it is certainly a component of the sought after solution.
Time to test the theories!