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:

Despite some impressive results, Arsenal’s underlying performances just don’t look as convincing this season as they did 12 months ago. However, their previous big overachievement came just before that improvement in expected goal difference, so perhaps this one will have a similar rallying effect?

After their promotion in 2014/15, Bournemouth look to have adjusted relatively well to the Premier League. While generally negative, their expected goal difference has remained relatively close to zero and occasionally shaded into the positive.

That’s a lot of blue! Burnley have been consistently overachieving since the start of last season in a way that I don’t think anyone else has. It’s tempting to conclude that Sean Dyche has hit upon a way to gain an edge that has yet to be neutralised by the majority of his opponents, given how well the two lines track each other.

The red shading around Chelsea’s horror start under Jose Mourinho last season suggests that it made them look a bit worse than they probably were. My model isn’t yet as convinced by Chelsea’s title credentials as some of the others I’ve seen because their rise in goal difference is massively outstripping their expected goals. Of course they may well be able to sustain that overachievement, given that their resources enable them to recruit players of above-average quality.

Alan Pardew had been consistently underachieving for almost a year prior to his sacking, but Palace looked far from terrible during his tenure. Perhaps their almost-as-long period of overachievement beforehand had raised expectations and made a rod for his back.

Apart from a flattering start to last season, Everton’s actual and expected goal difference have tracked each other pretty closely over the last two and half years. Both lines fell sharply prior to Roberto Martinez’s sacking at the end of 2015/16, despite having looked relatively healthy not long beforehand. Ronald Koeman presided over an immediate and rapid improvement in their fortunes which has also since swung back into the negative.

Hull looked a bit unlucky to be relegated from the top flight in 2014/15, having underachieved on some pretty respectable performances towards the end of the season. A similarly disappointing end to last season saw them return via the play-offs and they’ve endured the typical sharp shock of a newly-promoted Premier League team this time around.

Leicester’s title-winning season was one of continuous overachievement, but that gap has vanished this time around. Performances and results are now tracking each other closely and have dipped into the negative, although not so much as to make relegation an immediate concern.

The red line (showing the balance of chances created) has been gradually heading upwards since Jurgen Klopp joined last October, which is good news for the long term. After an underachieving start, followed by a pleasant blue peak towards the end of last season, Liverpool’s actual goal difference is now tracking their rising expected goals difference closely.

After an unsustainably good start last season, City’s performances ebbed before gradually improving as the campaign drew to a close. Under Guardiola they’ve improved still further (the red line is back to being almost as high as early last season), with their recent poor form looking more like a blip at the moment.

It’s been a mad few seasons for United, with both lines veering wildly and mostly in opposite directions. Their underlying performances – the red line – look far healthier now then they did towards the end of last season when some decent results appeared to be masking a worrying decline. The blue line is now rising again after four successive victories and nine games without defeat, so the two should achieve a rare convergence in the coming weeks.

Middlesbrough recovered well from a disappointing end to 2014/15 to secure promotion to the Premier League last season, and have since followed quite a common trajectory. Both lines have fallen sharply and then stabilised in the negative, reflecting the higher standard of opposition, and it looks like they’ve been overachieving slightly in recent matches.

After a bright start to 2014/15, Southampton have merrily cantered along as an above-average Premier League side with only a few brief excursions into negative territory. Both lines are dropping worryingly at the moment but it’s too soon to say whether they’ll plumb fresh depths given the absence of scary teams from their next seven fixtures.

After a long period of almost uncanny stability, the wheels fell off rapidly for Stoke towards the end of last season. The nadir was reached early this term, although the Potters have since rebounded impressively and both lines are more or less where they were a year ago.

Things seemed to be looking up for Sunderland after Sam Allardyce took over last season, with a clear upward swing in both lines towards positive territory. However that progress has been reversed this term and they’re now hovering at a similar level to before his arrival.

Swansea look to be on course to complete a pattern of “overachieve-underachieve-overachieve” for the third successive season. However the average position of the lines is dangerously lower than before, although under Bob Bradley the expected goals difference did seem to be edging in the right direction.

While their fifth-placed finish in 2014/15 was secured on the back of some relatively forgettable underlying performances, Spurs looked far stronger last season. With both lines on the rise this season after an early ebb, they look to be on course to challenge for a top four place yet again.

Since some clinical finishing saw them promoted to the Premier League in 2014/15, Watford’s actual and expected goal differences have tracked each other very closely. After a bright spell fizzled out this time last year, the Hornets’ decline was arrested by changes over the summer, but it’s not yet clear whether they’ll fall back or stabilise at an improved level.

You can just about make out a gradual upward trend in West Brom’s fortunes over the last season and a half, although the progression is far from steady. Having started this season in undeserved-looking poor form, their recent improvement in results coincided with some poorer underlying performances.

Having spent the best part of two seasons performing at a higher level than appeared sustainable, it’s perhaps only fair that West Ham have been underachieving this term. However their underlying expected goals difference has also dropped from its early peak, although is still slightly higher than the start of last season.