I’ve used the Christmas break to get another new type of graphic finished, which is explained in full here and briefly below.

Explanation

Basically these are adapted from a very similar design by the excellent Swedish blogger Zorba138 intended to track both long-term performance and whether this was an underachievement or an overachievement based on the balance of chances created.

There are two lines: one showing the rolling average of a club’s goal difference over the last 10 league games (blue line) and the other the rolling average of their expected goal difference (red line) based on the quality of chances they’ve created and faced.

Comparing these two allows us to see not only how a club’s performances have changed over time, but also whether there were any differences between the balance of chances created (a useful measure of underlying performance) and goals scored.

These are highlighted in blue (where goal difference is higher than chances created, suggesting overachievement) and red (for the reverse, signalling potential underachievement).

Over the long term we’d expect the two lines to converge unless there’s a significant difference in a club’s attacking or defensive skill compared to the average for the division. We can’t tell from the data alone whether skill or luck is the cause, but the longer a difference persists the more I’d suspect the former.

The graphics

Below I’ve created a graphic for each club (in alphabetical order) with some short commentary for each:

Villa’s graph is dominated by red, suggesting that there were problems with execution on top of the poor performances in their previous two Premier League seasons. While things have improved this term, the steadily modest position of the red line says “top half” rather than “top six” at the moment.

Last season was a crazy one for Barnsley, swinging from massive underachievement in the first half to overachievement in the second. Despite a promising start to this campaign, their underlying performances have dipped worryingly and they could still find themselves in danger of relegation.

There’s more blue than red here, suggesting that the recently-departed Gary Rowett was getting far better results than the performances suggested. The fact that the red line spent virtually all of last season in negative territory means that the top half finish they secured was a significant overachievement. The recent dip in performances (which may have triggered Rowett’s exit) could well have been a self-correction rather than a decline.

Blackburn look to have underachieved a fair bit over the last calendar year, with plenty of red at the back end of last season and the start of this one. However they’ve not looked anywhere near as impressive as they did until the back end of the previous campaign.

Since the start of last season, Brentford’s performances have been pretty steady and “mid-table”-ish: the red line barely deviates from a zero expected goal difference. However the blue line is all over the place, with huge swings in results that are far more dramatic.

Until the back end of last season, Brighton’s results and performances had been tracking each other fairly closely, albeit with outcomes slightly worse overall than they could expect. However we’re now in the second of two recent spells in which they’re significantly outperforming the balance of chances created. Given the resources at their disposal, this may have something to do with the quality of their squad – we’ll see a similar pattern with Newcastle below.

The first season here is City’s promotion from League 1, with the tougher opposition in the Championship the following year unsurprisingly hitting their performances hard. It looks like the ship has been steadied since the second half of last season, despite a recent dip.

Both 2014/15 and 2015/16 saw the Brewers promoted, with their expected goal difference staying almost entirely positive throughout. After an alarming dip early this term their performances have largely recovered, although their results have yet to see a similar boost.

Cardiff’s horrible start to the season continued a downward trend that began at the back end of the previous campaign. However results looked far worse than the underlying performances, so perhaps there was no need to change managers, although there’s no guarantee that they’d have recovered as sharply.

Even at the lowest point of their horrible start to the season, Derby’s performances looked decent – they were never a bad side, although Nigel Pearson was clearly struggling to achieve a cutting edge up front. Under Steve McClaren they’re now into what appears to be a traditional “blue patch”.

The red line suggests that Fulham’s performances have been improving steadily since the middle of last season. A sticky patch at the start of this campaign appears to have been a blip and they look to be in fine form at the moment.

There’s far more red than blue on this chart, suggesting that Huddersfield have either been due some luck for a while or need to improve their execution in at least one of attack or defence. While results and performances have improved of late, the red line isn’t yet in what I’d deem to be promotion territory.

Worryingly for Ipswich their modest results this season look to have represented an overachievement on some pretty sluggish performances. Attack has been the problem this season and should undoubtedly be the focus in January.

Garry Monk looks to have started the season well – the red line has been in a far healthier position than either of the previous two campaigns – but recent performances have dipped worryingly. With Leeds having faced better marginally better chances than they’ve created over the past 10 games, they could struggle to sustain their top six place without some improvement.

Newcastle look a bit unfortunate to have been relegated last season, with their performances improving faster than results towards the end, but they’ve enjoyed themselves far more this time around. The streak of blue could have as much to do with the superior quality of their squad as any good fortune (as expected goals are calculated based on the average side) but I’d be worried about the recent dip in the red line.

Norwich are another side who were relegated despite some improving performances last season, but so far this time around they haven’t been able to match their previous promotion campaign. After a promising start they’re currently being out-scored and out-created, with Alex Neil understandably under pressure.

Forest are enjoying their best performances since the start of last season but – just as then – they aren’t getting the results to go with them at the moment. Each of the previous two campaigns have seen plenty of “boom and bust”, so a more stable season may be welcomed.

Preston’s adjustment to life back in the second tier last season is clearly visible here: an initial cratering followed by a quick return to stability. They’ve oscillated relatively calmly about the zero goal difference mark ever since, with some modest recent overachievement compensating for a poor start.

It looks like QPR were already improving under Chris Ramsey before he was sacked last November, and the streak of blue at the end of last season suggests that a decent run of results under Jimmy Floyd Hasselbaink may have masked some underlying issues. Both lines are currently tanking heavily, suggesting that there may be more managerial changes in the near future.

Reading are my model’s nemesis at the moment, with their recent overachievement putting them far higher in the table than the underlying data suggests. However given that their results over the past few seasons have tended to be worse than their performances, it’s difficult to begrudge a bit of blue on their chart.

After a horrible start, Rotherham look to be gradually improving. The “Warnock effect” at the end of last season is clearly visible as a huge blue peak, suggesting that goal difference surged far more noticeably than the balance of chances. It’s therefore unclear whether he could have sustained those performances if he’d stuck around.

If you just focus on the red line, the Owls’ performances have been getting steadily better since early last season. However they haven’t enjoyed the good fortune that followed them for most of 2015/16, so they’ve flown under the radar a bit so far, but their blue line has been edging towards the red and they could be about to find another gear.

Wigan’s previous two seasons have featured a relegation and a promotion, and they’re in danger of bookending the latter with a drop back into League 1 as it stands. Performances have dropped just as sharply as results and they’re currently at a similar level to their previous exit from this division.

After a rollercoaster 2014/15 in which their results swung wildly despite some relatively stable performances, Wolves’ fortunes have tracked their showing on the pitch pretty faithfully in the last 18 months. Walter Zenga looked to be sustaining a decent level of performance before his surprising sacking.